{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
  "asList", methodType(List.class, Object[].class));
assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
         * }</pre>
         * @param refc the class from which the method is accessed
         * @param name the name of the method
         * @param type the type of the method
         * @return the desired method handle
         * @throws NoSuchMethodException if the method does not exist
         * @throws IllegalAccessException if access checking fails,
         *                                or if the method is not {@code static},
         *                                or if the method's variable arity modifier bit
         *                                is set and {@code asVarargsCollector} fails
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         */
        public
        MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
            MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
            return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
        }

        /**
         * Produces a method handle for a virtual method.
         * The type of the method handle will be that of the method,
         * with the receiver type (usually {@code refc}) prepended.
         * The method and all its argument types must be accessible to the lookup object.
         * <p>
         * When called, the handle will treat the first argument as a receiver
         * and dispatch on the receiver's type to determine which method
         * implementation to enter.
         * (The dispatching action is identical with that performed by an
         * {@code invokevirtual} or {@code invokeinterface} instruction.)
         * <p>
         * The first argument will be of type {@code refc} if the lookup
         * class has full privileges to access the member.  Otherwise
         * the member must be {@code protected} and the first argument
         * will be restricted in type to the lookup class.
         * <p>
         * The returned method handle will have
         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
         * the method's variable arity modifier bit ({@code 0x0080}) is set.
         * <p>
         * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence between {@code invokevirtual}
         * instructions and method handles produced by {@code findVirtual},
         * if the class is {@code MethodHandle} and the name string is
         * {@code invokeExact} or {@code invoke}, the resulting
         * method handle is equivalent to one produced by
         * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
         * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
         * with the same {@code type} argument.
         *
         * <b>Example:
         * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle MH_concat = publicLookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
  "hashCode", methodType(int.class));
MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
  "hashCode", methodType(int.class));
assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
// interface method:
MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
  "subSequence", methodType(CharSequence.class, int.class, int.class));
assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
// constructor "internal method" must be accessed differently:
MethodType MT_newString = methodType(void.class); //()V for new String()
try { assertEquals("impossible", lookup()
        .findVirtual(String.class, "<init>", MT_newString));
 } catch (NoSuchMethodException ex) { } // OK
MethodHandle MH_newString = publicLookup()
  .findConstructor(String.class, MT_newString);
assertEquals("", (String) MH_newString.invokeExact());
         * }</pre>
         *
         * @param refc the class or interface from which the method is accessed
         * @param name the name of the method
         * @param type the type of the method, with the receiver argument omitted
         * @return the desired method handle
         * @throws NoSuchMethodException if the method does not exist
         * @throws IllegalAccessException if access checking fails,
         *                                or if the method is {@code static}
         *                                or if the method's variable arity modifier bit
         *                                is set and {@code asVarargsCollector} fails
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         */
        public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
            if (refc == MethodHandle.class) {
                MethodHandle mh = findVirtualForMH(name, type);
                if (mh != null)  return mh;
            }
            byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
            MemberName method = resolveOrFail(refKind, refc, name, type);
            return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
        }
        private MethodHandle findVirtualForMH(String name, MethodType type) {
            // these names require special lookups because of the implicit MethodType argument
            if ("invoke".equals(name))
                return invoker(type);
            if ("invokeExact".equals(name))
                return exactInvoker(type);
            assert(!MemberName.isMethodHandleInvokeName(name));
            return null;
        }

        /**
         * Produces a method handle which creates an object and initializes it, using
         * the constructor of the specified type.
         * The parameter types of the method handle will be those of the constructor,
         * while the return type will be a reference to the constructor's class.
         * The constructor and all its argument types must be accessible to the lookup object.
         * <p>
         * The requested type must have a return type of {@code void}.
         * (This is consistent with the JVM's treatment of constructor type descriptors.)
         * <p>
         * The returned method handle will have
         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
         * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
         * <p>
         * If the returned method handle is invoked, the constructor's class will
         * be initialized, if it has not already been initialized.
         * <p>Example:
         * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle MH_newArrayList = publicLookup().findConstructor(
  ArrayList.class, methodType(void.class, Collection.class));
Collection orig = Arrays.asList("x", "y");
Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
assert(orig != copy);
assertEquals(orig, copy);
// a variable-arity constructor:
MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
  ProcessBuilder.class, methodType(void.class, String[].class));
ProcessBuilder pb = (ProcessBuilder)
  MH_newProcessBuilder.invoke("x", "y", "z");
assertEquals("[x, y, z]", pb.command().toString());
         * }</pre>
         * @param refc the class or interface from which the method is accessed
         * @param type the type of the method, with the receiver argument omitted, and a void return type
         * @return the desired method handle
         * @throws NoSuchMethodException if the constructor does not exist
         * @throws IllegalAccessException if access checking fails
         *                                or if the method's variable arity modifier bit
         *                                is set and {@code asVarargsCollector} fails
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         */
        public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
            String name = "<init>";
            MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
            return getDirectConstructor(refc, ctor);
        }

        /**
         * Produces an early-bound method handle for a virtual method.
         * It will bypass checks for overriding methods on the receiver,
         * <a href="MethodHandles.Lookup.html#equiv">as if called from an {@code invokespecial}
         * instruction from within the explicitly specified {@code specialCaller}.
         * The type of the method handle will be that of the method,
         * with a suitably restricted receiver type prepended.
         * (The receiver type will be {@code specialCaller} or a subtype.)
         * The method and all its argument types must be accessible
         * to the lookup object.
         * <p>
         * Before method resolution,
         * if the explicitly specified caller class is not identical with the
         * lookup class, or if this lookup object does not have
         * <a href="MethodHandles.Lookup.html#privacc">private access
         * privileges, the access fails.
         * <p>
         * The returned method handle will have
         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
         * the method's variable arity modifier bit ({@code 0x0080}) is set.
         * <p style="font-size:smaller;">
         * <em>(Note:  JVM internal methods named {@code ""} are not visible to this API,
         * even though the {@code invokespecial} instruction can refer to them
         * in special circumstances.  Use {@link #findConstructor findConstructor}
         * to access instance initialization methods in a safe manner.)</em>
         * <p>Example:
         * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
static class Listie extends ArrayList {
  public String toString() { return "[wee Listie]"; }
  static Lookup lookup() { return MethodHandles.lookup(); }
}
...
// no access to constructor via invokeSpecial:
MethodHandle MH_newListie = Listie.lookup()
  .findConstructor(Listie.class, methodType(void.class));
Listie l = (Listie) MH_newListie.invokeExact();
try { assertEquals("impossible", Listie.lookup().findSpecial(
        Listie.class, "<init>", methodType(void.class), Listie.class));
 } catch (NoSuchMethodException ex) { } // OK
// access to super and self methods via invokeSpecial:
MethodHandle MH_super = Listie.lookup().findSpecial(
  ArrayList.class, "toString" , methodType(String.class), Listie.class);
MethodHandle MH_this = Listie.lookup().findSpecial(
  Listie.class, "toString" , methodType(String.class), Listie.class);
MethodHandle MH_duper = Listie.lookup().findSpecial(
  Object.class, "toString" , methodType(String.class), Listie.class);
assertEquals("[]", (String) MH_super.invokeExact(l));
assertEquals(""+l, (String) MH_this.invokeExact(l));
assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
try { assertEquals("inaccessible", Listie.lookup().findSpecial(
        String.class, "toString", methodType(String.class), Listie.class));
 } catch (IllegalAccessException ex) { } // OK
Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
         * }</pre>
         *
         * @param refc the class or interface from which the method is accessed
         * @param name the name of the method (which must not be "<init>")
         * @param type the type of the method, with the receiver argument omitted
         * @param specialCaller the proposed calling class to perform the {@code invokespecial}
         * @return the desired method handle
         * @throws NoSuchMethodException if the method does not exist
         * @throws IllegalAccessException if access checking fails
         *                                or if the method's variable arity modifier bit
         *                                is set and {@code asVarargsCollector} fails
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         */
        public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
                                        Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
            checkSpecialCaller(specialCaller);
            Lookup specialLookup = this.in(specialCaller);
            MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
            return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
        }

        /**
         * Produces a method handle giving read access to a non-static field.
         * The type of the method handle will have a return type of the field's
         * value type.
         * The method handle's single argument will be the instance containing
         * the field.
         * Access checking is performed immediately on behalf of the lookup class.
         * @param refc the class or interface from which the method is accessed
         * @param name the field's name
         * @param type the field's type
         * @return a method handle which can load values from the field
         * @throws NoSuchFieldException if the field does not exist
         * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         */
        public MethodHandle findGetter(Class<?> refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
            MemberName field = resolveOrFail(REF_getField, refc, name, type);
            return getDirectField(REF_getField, refc, field);
        }

        /**
         * Produces a method handle giving write access to a non-static field.
         * The type of the method handle will have a void return type.
         * The method handle will take two arguments, the instance containing
         * the field, and the value to be stored.
         * The second argument will be of the field's value type.
         * Access checking is performed immediately on behalf of the lookup class.
         * @param refc the class or interface from which the method is accessed
         * @param name the field's name
         * @param type the field's type
         * @return a method handle which can store values into the field
         * @throws NoSuchFieldException if the field does not exist
         * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         */
        public MethodHandle findSetter(Class<?> refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
            MemberName field = resolveOrFail(REF_putField, refc, name, type);
            return getDirectField(REF_putField, refc, field);
        }

        /**
         * Produces a method handle giving read access to a static field.
         * The type of the method handle will have a return type of the field's
         * value type.
         * The method handle will take no arguments.
         * Access checking is performed immediately on behalf of the lookup class.
         * <p>
         * If the returned method handle is invoked, the field's class will
         * be initialized, if it has not already been initialized.
         * @param refc the class or interface from which the method is accessed
         * @param name the field's name
         * @param type the field's type
         * @return a method handle which can load values from the field
         * @throws NoSuchFieldException if the field does not exist
         * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         */
        public MethodHandle findStaticGetter(Class<?> refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
            MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
            return getDirectField(REF_getStatic, refc, field);
        }

        /**
         * Produces a method handle giving write access to a static field.
         * The type of the method handle will have a void return type.
         * The method handle will take a single
         * argument, of the field's value type, the value to be stored.
         * Access checking is performed immediately on behalf of the lookup class.
         * <p>
         * If the returned method handle is invoked, the field's class will
         * be initialized, if it has not already been initialized.
         * @param refc the class or interface from which the method is accessed
         * @param name the field's name
         * @param type the field's type
         * @return a method handle which can store values into the field
         * @throws NoSuchFieldException if the field does not exist
         * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         */
        public MethodHandle findStaticSetter(Class<?> refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
            MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
            return getDirectField(REF_putStatic, refc, field);
        }

        /**
         * Produces an early-bound method handle for a non-static method.
         * The receiver must have a supertype {@code defc} in which a method
         * of the given name and type is accessible to the lookup class.
         * The method and all its argument types must be accessible to the lookup object.
         * The type of the method handle will be that of the method,
         * without any insertion of an additional receiver parameter.
         * The given receiver will be bound into the method handle,
         * so that every call to the method handle will invoke the
         * requested method on the given receiver.
         * <p>
         * The returned method handle will have
         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
         * the method's variable arity modifier bit ({@code 0x0080}) is set
         * <em>and the trailing array argument is not the only argument.
         * (If the trailing array argument is the only argument,
         * the given receiver value will be bound to it.)
         * <p>
         * This is equivalent to the following code:
         * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle mh0 = lookup().findVirtual(defc, name, type);
MethodHandle mh1 = mh0.bindTo(receiver);
MethodType mt1 = mh1.type();
if (mh0.isVarargsCollector())
  mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
return mh1;
         * }</pre>
         * where {@code defc} is either {@code receiver.getClass()} or a super
         * type of that class, in which the requested method is accessible
         * to the lookup class.
         * (Note that {@code bindTo} does not preserve variable arity.)
         * @param receiver the object from which the method is accessed
         * @param name the name of the method
         * @param type the type of the method, with the receiver argument omitted
         * @return the desired method handle
         * @throws NoSuchMethodException if the method does not exist
         * @throws IllegalAccessException if access checking fails
         *                                or if the method's variable arity modifier bit
         *                                is set and {@code asVarargsCollector} fails
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws NullPointerException if any argument is null
         * @see MethodHandle#bindTo
         * @see #findVirtual
         */
        public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
            Class<? extends Object> refc = receiver.getClass(); // may get NPE
            MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
            MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
            return mh.bindReceiver(receiver).setVarargs(method);
        }

        /**
         * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle
         * to <i>m, if the lookup class has permission.
         * If <i>m is non-static, the receiver argument is treated as an initial argument.
         * If <i>m is virtual, overriding is respected on every call.
         * Unlike the Core Reflection API, exceptions are <em>not wrapped.
         * The type of the method handle will be that of the method,
         * with the receiver type prepended (but only if it is non-static).
         * If the method's {@code accessible} flag is not set,
         * access checking is performed immediately on behalf of the lookup class.
         * If <i>m is not public, do not share the resulting handle with untrusted parties.
         * <p>
         * The returned method handle will have
         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
         * the method's variable arity modifier bit ({@code 0x0080}) is set.
         * <p>
         * If <i>m is static, and
         * if the returned method handle is invoked, the method's class will
         * be initialized, if it has not already been initialized.
         * @param m the reflected method
         * @return a method handle which can invoke the reflected method
         * @throws IllegalAccessException if access checking fails
         *                                or if the method's variable arity modifier bit
         *                                is set and {@code asVarargsCollector} fails
         * @throws NullPointerException if the argument is null
         */
        public MethodHandle unreflect(Method m) throws IllegalAccessException {
            if (m.getDeclaringClass() == MethodHandle.class) {
                MethodHandle mh = unreflectForMH(m);
                if (mh != null)  return mh;
            }
            MemberName method = new MemberName(m);
            byte refKind = method.getReferenceKind();
            if (refKind == REF_invokeSpecial)
                refKind = REF_invokeVirtual;
            assert(method.isMethod());
            Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
            return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
        }
        private MethodHandle unreflectForMH(Method m) {
            // these names require special lookups because they throw UnsupportedOperationException
            if (MemberName.isMethodHandleInvokeName(m.getName()))
                return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
            return null;
        }

        /**
         * Produces a method handle for a reflected method.
         * It will bypass checks for overriding methods on the receiver,
         * <a href="MethodHandles.Lookup.html#equiv">as if called from an {@code invokespecial}
         * instruction from within the explicitly specified {@code specialCaller}.
         * The type of the method handle will be that of the method,
         * with a suitably restricted receiver type prepended.
         * (The receiver type will be {@code specialCaller} or a subtype.)
         * If the method's {@code accessible} flag is not set,
         * access checking is performed immediately on behalf of the lookup class,
         * as if {@code invokespecial} instruction were being linked.
         * <p>
         * Before method resolution,
         * if the explicitly specified caller class is not identical with the
         * lookup class, or if this lookup object does not have
         * <a href="MethodHandles.Lookup.html#privacc">private access
         * privileges, the access fails.
         * <p>
         * The returned method handle will have
         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
         * the method's variable arity modifier bit ({@code 0x0080}) is set.
         * @param m the reflected method
         * @param specialCaller the class nominally calling the method
         * @return a method handle which can invoke the reflected method
         * @throws IllegalAccessException if access checking fails
         *                                or if the method's variable arity modifier bit
         *                                is set and {@code asVarargsCollector} fails
         * @throws NullPointerException if any argument is null
         */
        public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
            checkSpecialCaller(specialCaller);
            Lookup specialLookup = this.in(specialCaller);
            MemberName method = new MemberName(m, true);
            assert(method.isMethod());
            // ignore m.isAccessible:  this is a new kind of access
            return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
        }

        /**
         * Produces a method handle for a reflected constructor.
         * The type of the method handle will be that of the constructor,
         * with the return type changed to the declaring class.
         * The method handle will perform a {@code newInstance} operation,
         * creating a new instance of the constructor's class on the
         * arguments passed to the method handle.
         * <p>
         * If the constructor's {@code accessible} flag is not set,
         * access checking is performed immediately on behalf of the lookup class.
         * <p>
         * The returned method handle will have
         * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
         * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
         * <p>
         * If the returned method handle is invoked, the constructor's class will
         * be initialized, if it has not already been initialized.
         * @param c the reflected constructor
         * @return a method handle which can invoke the reflected constructor
         * @throws IllegalAccessException if access checking fails
         *                                or if the method's variable arity modifier bit
         *                                is set and {@code asVarargsCollector} fails
         * @throws NullPointerException if the argument is null
         */
        public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
            MemberName ctor = new MemberName(c);
            assert(ctor.isConstructor());
            Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
            return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
        }

        /**
         * Produces a method handle giving read access to a reflected field.
         * The type of the method handle will have a return type of the field's
         * value type.
         * If the field is static, the method handle will take no arguments.
         * Otherwise, its single argument will be the instance containing
         * the field.
         * If the field's {@code accessible} flag is not set,
         * access checking is performed immediately on behalf of the lookup class.
         * <p>
         * If the field is static, and
         * if the returned method handle is invoked, the field's class will
         * be initialized, if it has not already been initialized.
         * @param f the reflected field
         * @return a method handle which can load values from the reflected field
         * @throws IllegalAccessException if access checking fails
         * @throws NullPointerException if the argument is null
         */
        public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
            return unreflectField(f, false);
        }
        private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
            MemberName field = new MemberName(f, isSetter);
            assert(isSetter
                    ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
                    : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
            Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
            return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
        }

        /**
         * Produces a method handle giving write access to a reflected field.
         * The type of the method handle will have a void return type.
         * If the field is static, the method handle will take a single
         * argument, of the field's value type, the value to be stored.
         * Otherwise, the two arguments will be the instance containing
         * the field, and the value to be stored.
         * If the field's {@code accessible} flag is not set,
         * access checking is performed immediately on behalf of the lookup class.
         * <p>
         * If the field is static, and
         * if the returned method handle is invoked, the field's class will
         * be initialized, if it has not already been initialized.
         * @param f the reflected field
         * @return a method handle which can store values into the reflected field
         * @throws IllegalAccessException if access checking fails
         * @throws NullPointerException if the argument is null
         */
        public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
            return unreflectField(f, true);
        }

        /**
         * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle
         * created by this lookup object or a similar one.
         * Security and access checks are performed to ensure that this lookup object
         * is capable of reproducing the target method handle.
         * This means that the cracking may fail if target is a direct method handle
         * but was created by an unrelated lookup object.
         * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive
         * and was created by a lookup object for a different class.
         * @param target a direct method handle to crack into symbolic reference components
         * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
         * @exception SecurityException if a security manager is present and it
         *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access
         * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
         * @exception NullPointerException if the target is {@code null}
         * @see MethodHandleInfo
         * @since 1.8
         */
        public MethodHandleInfo revealDirect(MethodHandle target) {
            MemberName member = target.internalMemberName();
            if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
                throw newIllegalArgumentException("not a direct method handle");
            Class<?> defc = member.getDeclaringClass();
            byte refKind = member.getReferenceKind();
            assert(MethodHandleNatives.refKindIsValid(refKind));
            if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
                // Devirtualized method invocation is usually formally virtual.
                // To avoid creating extra MemberName objects for this common case,
                // we encode this extra degree of freedom using MH.isInvokeSpecial.
                refKind = REF_invokeVirtual;
            if (refKind == REF_invokeVirtual && defc.isInterface())
                // Symbolic reference is through interface but resolves to Object method (toString, etc.)
                refKind = REF_invokeInterface;
            // Check SM permissions and member access before cracking.
            try {
                checkAccess(refKind, defc, member);
                checkSecurityManager(defc, member);
            } catch (IllegalAccessException ex) {
                throw new IllegalArgumentException(ex);
            }
            if (allowedModes != TRUSTED && member.isCallerSensitive()) {
                Class<?> callerClass = target.internalCallerClass();
                if (!hasPrivateAccess() || callerClass != lookupClass())
                    throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
            }
            // Produce the handle to the results.
            return new InfoFromMemberName(this, member, refKind);
        }

        /// Helper methods, all package-private.

        MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
            checkSymbolicClass(refc);  // do this before attempting to resolve
            name.getClass();  // NPE
            type.getClass();  // NPE
            return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
                                            NoSuchFieldException.class);
        }

        MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
            checkSymbolicClass(refc);  // do this before attempting to resolve
            name.getClass();  // NPE
            type.getClass();  // NPE
            checkMethodName(refKind, name);  // NPE check on name
            return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
                                            NoSuchMethodException.class);
        }

        MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
            checkSymbolicClass(member.getDeclaringClass());  // do this before attempting to resolve
            member.getName().getClass();  // NPE
            member.getType().getClass();  // NPE
            return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
                                            ReflectiveOperationException.class);
        }

        void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
            refc.getClass();  // NPE
            Class<?> caller = lookupClassOrNull();
            if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
                throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
        }

        /** Check name for an illegal leading "<" character. */
        void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
            if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
                throw new NoSuchMethodException("illegal method name: "+name);
        }


        /**
         * Find my trustable caller class if m is a caller sensitive method.
         * If this lookup object has private access, then the caller class is the lookupClass.
         * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
         */
        Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
            Class<?> callerClass = null;
            if (MethodHandleNatives.isCallerSensitive(m)) {
                // Only lookups with private access are allowed to resolve caller-sensitive methods
                if (hasPrivateAccess()) {
                    callerClass = lookupClass;
                } else {
                    throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
                }
            }
            return callerClass;
        }

        private boolean hasPrivateAccess() {
            return (allowedModes & PRIVATE) != 0;
        }

        /**
         * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks.
         * Determines a trustable caller class to compare with refc, the symbolic reference class.
         * If this lookup object has private access, then the caller class is the lookupClass.
         */
        void checkSecurityManager(Class<?> refc, MemberName m) {
            SecurityManager smgr = System.getSecurityManager();
            if (smgr == null)  return;
            if (allowedModes == TRUSTED)  return;

            // Step 1:
            boolean fullPowerLookup = hasPrivateAccess();
            if (!fullPowerLookup ||
                !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
                ReflectUtil.checkPackageAccess(refc);
            }

            // Step 2:
            if (m.isPublic()) return;
            if (!fullPowerLookup) {
                smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
            }

            // Step 3:
            Class<?> defc = m.getDeclaringClass();
            if (!fullPowerLookup && defc != refc) {
                ReflectUtil.checkPackageAccess(defc);
            }
        }

        void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
            boolean wantStatic = (refKind == REF_invokeStatic);
            String message;
            if (m.isConstructor())
                message = "expected a method, not a constructor";
            else if (!m.isMethod())
                message = "expected a method";
            else if (wantStatic != m.isStatic())
                message = wantStatic ? "expected a static method" : "expected a non-static method";
            else
                { checkAccess(refKind, refc, m); return; }
            throw m.makeAccessException(message, this);
        }

        void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
            boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
            String message;
            if (wantStatic != m.isStatic())
                message = wantStatic ? "expected a static field" : "expected a non-static field";
            else
                { checkAccess(refKind, refc, m); return; }
            throw m.makeAccessException(message, this);
        }

        /** Check public/protected/private bits on the symbolic reference class and its member. */
        void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
            assert(m.referenceKindIsConsistentWith(refKind) &&
                   MethodHandleNatives.refKindIsValid(refKind) &&
                   (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
            int allowedModes = this.allowedModes;
            if (allowedModes == TRUSTED)  return;
            int mods = m.getModifiers();
            if (Modifier.isProtected(mods) &&
                    refKind == REF_invokeVirtual &&
                    m.getDeclaringClass() == Object.class &&
                    m.getName().equals("clone") &&
                    refc.isArray()) {
                // The JVM does this hack also.
                // (See ClassVerifier::verify_invoke_instructions
                // and LinkResolver::check_method_accessability.)
                // Because the JVM does not allow separate methods on array types,
                // there is no separate method for int[].clone.
                // All arrays simply inherit Object.clone.
                // But for access checking logic, we make Object.clone
                // (normally protected) appear to be public.
                // Later on, when the DirectMethodHandle is created,
                // its leading argument will be restricted to the
                // requested array type.
                // N.B. The return type is not adjusted, because
                // that is *not* the bytecode behavior.
                mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
            }
            if (Modifier.isFinal(mods) &&
                    MethodHandleNatives.refKindIsSetter(refKind))
                throw m.makeAccessException("unexpected set of a final field", this);
            if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
                return;  // common case
            int requestedModes = fixmods(mods);  // adjust 0 => PACKAGE
            if ((requestedModes & allowedModes) != 0) {
                if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
                                                    mods, lookupClass(), allowedModes))
                    return;
            } else {
                // Protected members can also be checked as if they were package-private.
                if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
                        && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
                    return;
            }
            throw m.makeAccessException(accessFailedMessage(refc, m), this);
        }

        String accessFailedMessage(Class<?> refc, MemberName m) {
            Class<?> defc = m.getDeclaringClass();
            int mods = m.getModifiers();
            // check the class first:
            boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
                               (defc == refc ||
                                Modifier.isPublic(refc.getModifiers())));
            if (!classOK && (allowedModes & PACKAGE) != 0) {
                classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
                           (defc == refc ||
                            VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
            }
            if (!classOK)
                return "class is not public";
            if (Modifier.isPublic(mods))
                return "access to public member failed";  // (how?)
            if (Modifier.isPrivate(mods))
                return "member is private";
            if (Modifier.isProtected(mods))
                return "member is protected";
            return "member is private to package";
        }

        private static final boolean ALLOW_NESTMATE_ACCESS = false;

        private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
            int allowedModes = this.allowedModes;
            if (allowedModes == TRUSTED)  return;
            if (!hasPrivateAccess()
                || (specialCaller != lookupClass()
                    && !(ALLOW_NESTMATE_ACCESS &&
                         VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
                throw new MemberName(specialCaller).
                    makeAccessException("no private access for invokespecial", this);
        }

        private boolean restrictProtectedReceiver(MemberName method) {
            // The accessing class only has the right to use a protected member
            // on itself or a subclass.  Enforce that restriction, from JVMS 5.4.4, etc.
            if (!method.isProtected() || method.isStatic()
                || allowedModes == TRUSTED
                || method.getDeclaringClass() == lookupClass()
                || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
                || (ALLOW_NESTMATE_ACCESS &&
                    VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
                return false;
            return true;
        }
        private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
            assert(!method.isStatic());
            // receiver type of mh is too wide; narrow to caller
            if (!method.getDeclaringClass().isAssignableFrom(caller)) {
                throw method.makeAccessException("caller class must be a subclass below the method", caller);
            }
            MethodType rawType = mh.type();
            if (rawType.parameterType(0) == caller)  return mh;
            MethodType narrowType = rawType.changeParameterType(0, caller);
            return mh.viewAsType(narrowType);
        }

        /** Check access and get the requested method. */
        private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class callerClass) throws IllegalAccessException {
            final boolean doRestrict    = true;
            final boolean checkSecurity = true;
            return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
        }
        /** Check access and get the requested method, eliding receiver narrowing rules. */
        private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class callerClass) throws IllegalAccessException {
            final boolean doRestrict    = false;
            final boolean checkSecurity = true;
            return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
        }
        /** Check access and get the requested method, eliding security manager checks. */
        private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class callerClass) throws IllegalAccessException {
            final boolean doRestrict    = true;
            final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
            return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
        }
        /** Common code for all methods; do not call directly except from immediately above. */
        private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
                                                   boolean checkSecurity,
                                                   boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
            checkMethod(refKind, refc, method);
            // Optionally check with the security manager; this isn't needed for unreflect* calls.
            if (checkSecurity)
                checkSecurityManager(refc, method);
            assert(!method.isMethodHandleInvoke());

            Class<?> refcAsSuper;
            if (refKind == REF_invokeSpecial &&
                refc != lookupClass() &&
                !refc.isInterface() &&
                refc != (refcAsSuper = lookupClass().getSuperclass()) &&
                refc.isAssignableFrom(lookupClass())) {
                assert(!method.getName().equals("<init>"));  // not this code path
                // Per JVMS 6.5, desc. of invokespecial instruction:
                // If the method is in a superclass of the LC,
                // and if our original search was above LC.super,
                // repeat the search (symbolic lookup) from LC.super.
                // FIXME: MemberName.resolve should handle this instead.
                MemberName m2 = new MemberName(refcAsSuper,
                                               method.getName(),
                                               method.getMethodType(),
                                               REF_invokeSpecial);
                m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
                if (m2 == null)  throw new InternalError(method.toString());
                method = m2;
                refc = refcAsSuper;
                // redo basic checks
                checkMethod(refKind, refc, method);
            }

            MethodHandle mh = DirectMethodHandle.make(refKind, refc, method);
            mh = maybeBindCaller(method, mh, callerClass);
            mh = mh.setVarargs(method);
            // Optionally narrow the receiver argument to refc using restrictReceiver.
            if (doRestrict &&
                   (refKind == REF_invokeSpecial ||
                       (MethodHandleNatives.refKindHasReceiver(refKind) &&
                           restrictProtectedReceiver(method))))
                mh = restrictReceiver(method, mh, lookupClass());
            return mh;
        }
        private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
                                             Class<?> callerClass)
                                             throws IllegalAccessException {
            if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
                return mh;
            Class<?> hostClass = lookupClass;
            if (!hasPrivateAccess())  // caller must have private access
                hostClass = callerClass;  // callerClass came from a security manager style stack walk
            MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
            // Note: caller will apply varargs after this step happens.
            return cbmh;
        }
        /** Check access and get the requested field. */
        private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
            final boolean checkSecurity = true;
            return getDirectFieldCommon(refKind, refc, field, checkSecurity);
        }
        /** Check access and get the requested field, eliding security manager checks. */
        private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
            final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
            return getDirectFieldCommon(refKind, refc, field, checkSecurity);
        }
        /** Common code for all fields; do not call directly except from immediately above. */
        private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
                                                  boolean checkSecurity) throws IllegalAccessException {
            checkField(refKind, refc, field);
            // Optionally check with the security manager; this isn't needed for unreflect* calls.
            if (checkSecurity)
                checkSecurityManager(refc, field);
            MethodHandle mh = DirectMethodHandle.make(refc, field);
            boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
                                    restrictProtectedReceiver(field));
            if (doRestrict)
                mh = restrictReceiver(field, mh, lookupClass());
            return mh;
        }
        /** Check access and get the requested constructor. */
        private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
            final boolean checkSecurity = true;
            return getDirectConstructorCommon(refc, ctor, checkSecurity);
        }
        /** Check access and get the requested constructor, eliding security manager checks. */
        private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
            final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
            return getDirectConstructorCommon(refc, ctor, checkSecurity);
        }
        /** Common code for all constructors; do not call directly except from immediately above. */
        private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
                                                  boolean checkSecurity) throws IllegalAccessException {
            assert(ctor.isConstructor());
            checkAccess(REF_newInvokeSpecial, refc, ctor);
            // Optionally check with the security manager; this isn't needed for unreflect* calls.
            if (checkSecurity)
                checkSecurityManager(refc, ctor);
            assert(!MethodHandleNatives.isCallerSensitive(ctor));  // maybeBindCaller not relevant here
            return DirectMethodHandle.make(ctor).setVarargs(ctor);
        }

        /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
         */
        /*non-public*/
        MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
            if (!(type instanceof Class || type instanceof MethodType))
                throw new InternalError("unresolved MemberName");
            MemberName member = new MemberName(refKind, defc, name, type);
            MethodHandle mh = LOOKASIDE_TABLE.get(member);
            if (mh != null) {
                checkSymbolicClass(defc);
                return mh;
            }
            // Treat MethodHandle.invoke and invokeExact specially.
            if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
                mh = findVirtualForMH(member.getName(), member.getMethodType());
                if (mh != null) {
                    return mh;
                }
            }
            MemberName resolved = resolveOrFail(refKind, member);
            mh = getDirectMethodForConstant(refKind, defc, resolved);
            if (mh instanceof DirectMethodHandle
                    && canBeCached(refKind, defc, resolved)) {
                MemberName key = mh.internalMemberName();
                if (key != null) {
                    key = key.asNormalOriginal();
                }
                if (member.equals(key)) {  // better safe than sorry
                    LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
                }
            }
            return mh;
        }
        private
        boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
            if (refKind == REF_invokeSpecial) {
                return false;
            }
            if (!Modifier.isPublic(defc.getModifiers()) ||
                    !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
                    !member.isPublic() ||
                    member.isCallerSensitive()) {
                return false;
            }
            ClassLoader loader = defc.getClassLoader();
            if (!sun.misc.VM.isSystemDomainLoader(loader)) {
                ClassLoader sysl = ClassLoader.getSystemClassLoader();
                boolean found = false;
                while (sysl != null) {
                    if (loader == sysl) { found = true; break; }
                    sysl = sysl.getParent();
                }
                if (!found) {
                    return false;
                }
            }
            try {
                MemberName resolved2 = publicLookup().resolveOrFail(refKind,
                    new MemberName(refKind, defc, member.getName(), member.getType()));
                checkSecurityManager(defc, resolved2);
            } catch (ReflectiveOperationException | SecurityException ex) {
                return false;
            }
            return true;
        }
        private
        MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
                throws ReflectiveOperationException {
            if (MethodHandleNatives.refKindIsField(refKind)) {
                return getDirectFieldNoSecurityManager(refKind, defc, member);
            } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
                return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
            } else if (refKind == REF_newInvokeSpecial) {
                return getDirectConstructorNoSecurityManager(defc, member);
            }
            // oops
            throw newIllegalArgumentException("bad MethodHandle constant #"+member);
        }

        static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
    }

    /**
     * Produces a method handle giving read access to elements of an array.
     * The type of the method handle will have a return type of the array's
     * element type.  Its first argument will be the array type,
     * and the second will be {@code int}.
     * @param arrayClass an array type
     * @return a method handle which can load values from the given array type
     * @throws NullPointerException if the argument is null
     * @throws  IllegalArgumentException if arrayClass is not an array type
     */
    public static
    MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
        return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
    }

    /**
     * Produces a method handle giving write access to elements of an array.
     * The type of the method handle will have a void return type.
     * Its last argument will be the array's element type.
     * The first and second arguments will be the array type and int.
     * @param arrayClass the class of an array
     * @return a method handle which can store values into the array type
     * @throws NullPointerException if the argument is null
     * @throws IllegalArgumentException if arrayClass is not an array type
     */
    public static
    MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
        return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
    }

    /// method handle invocation (reflective style)

    /**
     * Produces a method handle which will invoke any method handle of the
     * given {@code type}, with a given number of trailing arguments replaced by
     * a single trailing {@code Object[]} array.
     * The resulting invoker will be a method handle with the following
     * arguments:
     * <ul>
     * <li>a single {@code MethodHandle} target
     * <li>zero or more leading values (counted by {@code leadingArgCount})
     * <li>an {@code Object[]} array containing trailing arguments
     * </ul>
     * <p>
     * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
     * the indicated {@code type}.
     * That is, if the target is exactly of the given {@code type}, it will behave
     * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
     * is used to convert the target to the required {@code type}.
     * <p>
     * The type of the returned invoker will not be the given {@code type}, but rather
     * will have all parameters except the first {@code leadingArgCount}
     * replaced by a single array of type {@code Object[]}, which will be
     * the final parameter.
     * <p>
     * Before invoking its target, the invoker will spread the final array, apply
     * reference casts as necessary, and unbox and widen primitive arguments.
     * If, when the invoker is called, the supplied array argument does
     * not have the correct number of elements, the invoker will throw
     * an {@link IllegalArgumentException} instead of invoking the target.
     * <p>
     * This method is equivalent to the following code (though it may be more efficient):
     * <blockquote>
{@code
MethodHandle invoker = MethodHandles.invoker(type);
int spreadArgCount = type.parameterCount() - leadingArgCount;
invoker = invoker.asSpreader(Object[].class, spreadArgCount);
return invoker;
     * }</pre>
     * This method throws no reflective or security exceptions.
     * @param type the desired target type
     * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
     * @return a method handle suitable for invoking any method handle of the given type
     * @throws NullPointerException if {@code type} is null
     * @throws IllegalArgumentException if {@code leadingArgCount} is not in
     *                  the range from 0 to {@code type.parameterCount()} inclusive,
     *                  or if the resulting method handle's type would have
     *          <a href="MethodHandle.html#maxarity">too many parameters
     */
    static public
    MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
        if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
            throw new IllegalArgumentException("bad argument count "+leadingArgCount);
        return type.invokers().spreadInvoker(leadingArgCount);
    }

    /**
     * Produces a special <em>invoker method handle which can be used to
     * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
     * The resulting invoker will have a type which is
     * exactly equal to the desired type, except that it will accept
     * an additional leading argument of type {@code MethodHandle}.
     * <p>
     * This method is equivalent to the following code (though it may be more efficient):
     * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
     *
     * <p style="font-size:smaller;">
     * <em>Discussion:
     * Invoker method handles can be useful when working with variable method handles
     * of unknown types.
     * For example, to emulate an {@code invokeExact} call to a variable method
     * handle {@code M}, extract its type {@code T},
     * look up the invoker method {@code X} for {@code T},
     * and call the invoker method, as {@code X.invoke(T, A...)}.
     * (It would not work to call {@code X.invokeExact}, since the type {@code T}
     * is unknown.)
     * If spreading, collecting, or other argument transformations are required,
     * they can be applied once to the invoker {@code X} and reused on many {@code M}
     * method handle values, as long as they are compatible with the type of {@code X}.
     * <p style="font-size:smaller;">
     * <em>(Note:  The invoker method is not available via the Core Reflection API.
     * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
     * on the declared {@code invokeExact} or {@code invoke} method will raise an
     * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
     * <p>
     * This method throws no reflective or security exceptions.
     * @param type the desired target type
     * @return a method handle suitable for invoking any method handle of the given type
     * @throws IllegalArgumentException if the resulting method handle's type would have
     *          <a href="MethodHandle.html#maxarity">too many parameters
     */
    static public
    MethodHandle exactInvoker(MethodType type) {
        return type.invokers().exactInvoker();
    }

    /**
     * Produces a special <em>invoker method handle which can be used to
     * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
     * The resulting invoker will have a type which is
     * exactly equal to the desired type, except that it will accept
     * an additional leading argument of type {@code MethodHandle}.
     * <p>
     * Before invoking its target, if the target differs from the expected type,
     * the invoker will apply reference casts as
     * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
     * Similarly, the return value will be converted as necessary.
     * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
     * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
     * <p>
     * This method is equivalent to the following code (though it may be more efficient):
     * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
     * <p style="font-size:smaller;">
     * <em>Discussion:
     * A {@linkplain MethodType#genericMethodType general method type} is one which
     * mentions only {@code Object} arguments and return values.
     * An invoker for such a type is capable of calling any method handle
     * of the same arity as the general type.
     * <p style="font-size:smaller;">
     * <em>(Note:  The invoker method is not available via the Core Reflection API.
     * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
     * on the declared {@code invokeExact} or {@code invoke} method will raise an
     * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
     * <p>
     * This method throws no reflective or security exceptions.
     * @param type the desired target type
     * @return a method handle suitable for invoking any method handle convertible to the given type
     * @throws IllegalArgumentException if the resulting method handle's type would have
     *          <a href="MethodHandle.html#maxarity">too many parameters
     */
    static public
    MethodHandle invoker(MethodType type) {
        return type.invokers().generalInvoker();
    }

    static /*non-public*/
    MethodHandle basicInvoker(MethodType type) {
        return type.form().basicInvoker();
    }

     /// method handle modification (creation from other method handles)

    /**
     * Produces a method handle which adapts the type of the
     * given method handle to a new type by pairwise argument and return type conversion.
     * The original type and new type must have the same number of arguments.
     * The resulting method handle is guaranteed to report a type
     * which is equal to the desired new type.
     * <p>
     * If the original type and new type are equal, returns target.
     * <p>
     * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
     * and some additional conversions are also applied if those conversions fail.
     * Given types <em>T0, T1, one of the following conversions is applied
     * if possible, before or instead of any conversions done by {@code asType}:
     * <ul>
     * <li>If T0 and T1 are references, and T1 is an interface type,
     *     then the value of type <em>T0 is passed as a T1 without a cast.
     *     (This treatment of interfaces follows the usage of the bytecode verifier.)
     * <li>If T0 is boolean and T1 is another primitive,
     *     the boolean is converted to a byte value, 1 for true, 0 for false.
     *     (This treatment follows the usage of the bytecode verifier.)
     * <li>If T1 is boolean and T0 is another primitive,
     *     <em>T0 is converted to byte via Java casting conversion (JLS 5.5),
     *     and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
     * <li>If T0 and T1 are primitives other than boolean,
     *     then a Java casting conversion (JLS 5.5) is applied.
     *     (Specifically, <em>T0 will convert to T1 by
     *     widening and/or narrowing.)
     * <li>If T0 is a reference and T1 a primitive, an unboxing
     *     conversion will be applied at runtime, possibly followed
     *     by a Java casting conversion (JLS 5.5) on the primitive value,
     *     possibly followed by a conversion from byte to boolean by testing
     *     the low-order bit.
     * <li>If T0 is a reference and T1 a primitive,
     *     and if the reference is null at runtime, a zero value is introduced.
     * </ul>
     * @param target the method handle to invoke after arguments are retyped
     * @param newType the expected type of the new method handle
     * @return a method handle which delegates to the target after performing
     *           any necessary argument conversions, and arranges for any
     *           necessary return value conversions
     * @throws NullPointerException if either argument is null
     * @throws WrongMethodTypeException if the conversion cannot be made
     * @see MethodHandle#asType
     */
    public static
    MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
        if (!target.type().isCastableTo(newType)) {
            throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
        }
        return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
    }

    /**
     * Produces a method handle which adapts the calling sequence of the
     * given method handle to a new type, by reordering the arguments.
     * The resulting method handle is guaranteed to report a type
     * which is equal to the desired new type.
     * <p>
     * The given array controls the reordering.
     * Call {@code #I} the number of incoming parameters (the value
     * {@code newType.parameterCount()}, and call {@code #O} the number
     * of outgoing parameters (the value {@code target.type().parameterCount()}).
     * Then the length of the reordering array must be {@code #O},
     * and each element must be a non-negative number less than {@code #I}.
     * For every {@code N} less than {@code #O}, the {@code N}-th
     * outgoing argument will be taken from the {@code I}-th incoming
     * argument, where {@code I} is {@code reorder[N]}.
     * <p>
     * No argument or return value conversions are applied.
     * The type of each incoming argument, as determined by {@code newType},
     * must be identical to the type of the corresponding outgoing parameter
     * or parameters in the target method handle.
     * The return type of {@code newType} must be identical to the return
     * type of the original target.
     * <p>
     * The reordering array need not specify an actual permutation.
     * An incoming argument will be duplicated if its index appears
     * more than once in the array, and an incoming argument will be dropped
     * if its index does not appear in the array.
     * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
     * incoming arguments which are not mentioned in the reordering array
     * are may be any type, as determined only by {@code newType}.
     * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodType intfn1 = methodType(int.class, int.class);
MethodType intfn2 = methodType(int.class, int.class, int.class);
MethodHandle sub = ... (int x, int y) -> (x-y) ...;
assert(sub.type().equals(intfn2));
MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
assert((int)rsub.invokeExact(1, 100) == 99);
MethodHandle add = ... (int x, int y) -> (x+y) ...;
assert(add.type().equals(intfn2));
MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
assert(twice.type().equals(intfn1));
assert((int)twice.invokeExact(21) == 42);
     * }</pre>
     * @param target the method handle to invoke after arguments are reordered
     * @param newType the expected type of the new method handle
     * @param reorder an index array which controls the reordering
     * @return a method handle which delegates to the target after it
     *           drops unused arguments and moves and/or duplicates the other arguments
     * @throws NullPointerException if any argument is null
     * @throws IllegalArgumentException if the index array length is not equal to
     *                  the arity of the target, or if any index array element
     *                  not a valid index for a parameter of {@code newType},
     *                  or if two corresponding parameter types in
     *                  {@code target.type()} and {@code newType} are not identical,
     */
    public static
    MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
        checkReorder(reorder, newType, target.type());
        return target.permuteArguments(newType, reorder);
    }

    private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
        if (newType.returnType() != oldType.returnType())
            throw newIllegalArgumentException("return types do not match",
                    oldType, newType);
        if (reorder.length == oldType.parameterCount()) {
            int limit = newType.parameterCount();
            boolean bad = false;
            for (int j = 0; j < reorder.length; j++) {
                int i = reorder[j];
                if (i < 0 || i >= limit) {
                    bad = true; break;
                }
                Class<?> src = newType.parameterType(i);
                Class<?> dst = oldType.parameterType(j);
                if (src != dst)
                    throw newIllegalArgumentException("parameter types do not match after reorder",
                            oldType, newType);
            }
            if (!bad)  return;
        }
        throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
    }

    /**
     * Produces a method handle of the requested return type which returns the given
     * constant value every time it is invoked.
     * <p>
     * Before the method handle is returned, the passed-in value is converted to the requested type.
     * If the requested type is primitive, widening primitive conversions are attempted,
     * else reference conversions are attempted.
     * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
     * @param type the return type of the desired method handle
     * @param value the value to return
     * @return a method handle of the given return type and no arguments, which always returns the given value
     * @throws NullPointerException if the {@code type} argument is null
     * @throws ClassCastException if the value cannot be converted to the required return type
     * @throws IllegalArgumentException if the given type is {@code void.class}
     */
    public static
    MethodHandle constant(Class<?> type, Object value) {
        if (type.isPrimitive()) {
            if (type == void.class)
                throw newIllegalArgumentException("void type");
            Wrapper w = Wrapper.forPrimitiveType(type);
            return insertArguments(identity(type), 0, w.convert(value, type));
        } else {
            return identity(type).bindTo(type.cast(value));
        }
    }

    /**
     * Produces a method handle which returns its sole argument when invoked.
     * @param type the type of the sole parameter and return value of the desired method handle
     * @return a unary method handle which accepts and returns the given type
     * @throws NullPointerException if the argument is null
     * @throws IllegalArgumentException if the given type is {@code void.class}
     */
    public static
    MethodHandle identity(Class<?> type) {
        if (type == void.class)
            throw newIllegalArgumentException("void type");
        else if (type == Object.class)
            return ValueConversions.identity();
        else if (type.isPrimitive())
            return ValueConversions.identity(Wrapper.forPrimitiveType(type));
        else
            return MethodHandleImpl.makeReferenceIdentity(type);
    }

    /**
     * Provides a target method handle with one or more <em>bound arguments
     * in advance of the method handle's invocation.
     * The formal parameters to the target corresponding to the bound
     * arguments are called <em>bound parameters.
     * Returns a new method handle which saves away the bound arguments.
     * When it is invoked, it receives arguments for any non-bound parameters,
     * binds the saved arguments to their corresponding parameters,
     * and calls the original target.
     * <p>
     * The type of the new method handle will drop the types for the bound
     * parameters from the original target type, since the new method handle
     * will no longer require those arguments to be supplied by its callers.
     * <p>
     * Each given argument object must match the corresponding bound parameter type.
     * If a bound parameter type is a primitive, the argument object
     * must be a wrapper, and will be unboxed to produce the primitive value.
     * <p>
     * The {@code pos} argument selects which parameters are to be bound.
     * It may range between zero and <i>N-L (inclusively),
     * where <i>N is the arity of the target method handle
     * and <i>L is the length of the values array.
     * @param target the method handle to invoke after the argument is inserted
     * @param pos where to insert the argument (zero for the first)
     * @param values the series of arguments to insert
     * @return a method handle which inserts an additional argument,
     *         before calling the original method handle
     * @throws NullPointerException if the target or the {@code values} array is null
     * @see MethodHandle#bindTo
     */
    public static
    MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
        int insCount = values.length;
        MethodType oldType = target.type();
        int outargs = oldType.parameterCount();
        int inargs  = outargs - insCount;
        if (inargs < 0)
            throw newIllegalArgumentException("too many values to insert");
        if (pos < 0 || pos > inargs)
            throw newIllegalArgumentException("no argument type to append");
        MethodHandle result = target;
        for (int i = 0; i < insCount; i++) {
            Object value = values[i];
            Class<?> ptype = oldType.parameterType(pos+i);
            if (ptype.isPrimitive()) {
                char btype = 'I';
                Wrapper w = Wrapper.forPrimitiveType(ptype);
                switch (w) {
                case LONG:    btype = 'J'; break;
                case FLOAT:   btype = 'F'; break;
                case DOUBLE:  btype = 'D'; break;
                }
                // perform unboxing and/or primitive conversion
                value = w.convert(value, ptype);
                result = result.bindArgument(pos, btype, value);
                continue;
            }
            value = ptype.cast(value);  // throw CCE if needed
            if (pos == 0) {
                result = result.bindReceiver(value);
            } else {
                result = result.bindArgument(pos, 'L', value);
            }
        }
        return result;
    }

    /**
     * Produces a method handle which will discard some dummy arguments
     * before calling some other specified <i>target method handle.
     * The type of the new method handle will be the same as the target's type,
     * except it will also include the dummy argument types,
     * at some given position.
     * <p>
     * The {@code pos} argument may range between zero and <i>N,
     * where <i>N is the arity of the target.
     * If {@code pos} is zero, the dummy arguments will precede
     * the target's real arguments; if {@code pos} is <i>N
     * they will come after.
     * <p>
     * <b>Example:
     * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
assertEquals(bigType, d0.type());
assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
     * }</pre>
     * <p>
     * This method is also equivalent to the following code:
     * <blockquote>
     * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
     * </pre>
     * @param target the method handle to invoke after the arguments are dropped
     * @param valueTypes the type(s) of the argument(s) to drop
     * @param pos position of first argument to drop (zero for the leftmost)
     * @return a method handle which drops arguments of the given types,
     *         before calling the original method handle
     * @throws NullPointerException if the target is null,
     *                              or if the {@code valueTypes} list or any of its elements is null
     * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
     *                  or if {@code pos} is negative or greater than the arity of the target,
     *                  or if the new method handle's type would have too many parameters
     */
    public static
    MethodHandle dropArguments(MethodHandle target, int pos, List<Class valueTypes) {
        MethodType oldType = target.type();  // get NPE
        int dropped = valueTypes.size();
        MethodType.checkSlotCount(dropped);
        if (dropped == 0)  return target;
        int outargs = oldType.parameterCount();
        int inargs  = outargs + dropped;
        if (pos < 0 || pos >= inargs)
            throw newIllegalArgumentException("no argument type to remove");
        ArrayList<Class ptypes = new ArrayList<>(oldType.parameterList());
        ptypes.addAll(pos, valueTypes);
        MethodType newType = MethodType.methodType(oldType.returnType(), ptypes);
        return target.dropArguments(newType, pos, dropped);
    }

    /**
     * Produces a method handle which will discard some dummy arguments
     * before calling some other specified <i>target method handle.
     * The type of the new method handle will be the same as the target's type,
     * except it will also include the dummy argument types,
     * at some given position.
     * <p>
     * The {@code pos} argument may range between zero and <i>N,
     * where <i>N is the arity of the target.
     * If {@code pos} is zero, the dummy arguments will precede
     * the target's real arguments; if {@code pos} is <i>N
     * they will come after.
     * <p>
     * <b>Example:
     * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodHandle d0 = dropArguments(cat, 0, String.class);
assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
MethodHandle d1 = dropArguments(cat, 1, String.class);
assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
MethodHandle d2 = dropArguments(cat, 2, String.class);
assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
     * }</pre>
     * <p>
     * This method is also equivalent to the following code:
     * <blockquote>
     * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
     * </pre>
     * @param target the method handle to invoke after the arguments are dropped
     * @param valueTypes the type(s) of the argument(s) to drop
     * @param pos position of first argument to drop (zero for the leftmost)
     * @return a method handle which drops arguments of the given types,
     *         before calling the original method handle
     * @throws NullPointerException if the target is null,
     *                              or if the {@code valueTypes} array or any of its elements is null
     * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
     *                  or if {@code pos} is negative or greater than the arity of the target,
     *                  or if the new method handle's type would have
     *                  <a href="MethodHandle.html#maxarity">too many parameters
     */
    public static
    MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
        return dropArguments(target, pos, Arrays.asList(valueTypes));
    }

    /**
     * Adapts a target method handle by pre-processing
     * one or more of its arguments, each with its own unary filter function,
     * and then calling the target with each pre-processed argument
     * replaced by the result of its corresponding filter function.
     * <p>
     * The pre-processing is performed by one or more method handles,
     * specified in the elements of the {@code filters} array.
     * The first element of the filter array corresponds to the {@code pos}
     * argument of the target, and so on in sequence.
     * <p>
     * Null arguments in the array are treated as identity functions,
     * and the corresponding arguments left unchanged.
     * (If there are no non-null elements in the array, the original target is returned.)
     * Each filter is applied to the corresponding argument of the adapter.
     * <p>
     * If a filter {@code F} applies to the {@code N}th argument of
     * the target, then {@code F} must be a method handle which
     * takes exactly one argument.  The type of {@code F}'s sole argument
     * replaces the corresponding argument type of the target
     * in the resulting adapted method handle.
     * The return type of {@code F} must be identical to the corresponding
     * parameter type of the target.
     * <p>
     * It is an error if there are elements of {@code filters}
     * (null or not)
     * which do not correspond to argument positions in the target.
     * <p>Example:
     * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
MethodHandle upcase = lookup().findVirtual(String.class,
  "toUpperCase", methodType(String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodHandle f0 = filterArguments(cat, 0, upcase);
assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
MethodHandle f1 = filterArguments(cat, 1, upcase);
assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
     * }</pre>
     * <p> Here is pseudocode for the resulting adapter:
     * <blockquote>
{@code
     * V target(P... p, A[i]... a[i], B... b);
     * A[i] filter[i](V[i]);
     * T adapter(P... p, V[i]... v[i], B... b) {
     *   return target(p..., f[i](v[i])..., b...);
     * }
     * }</pre>
     *
     * @param target the method handle to invoke after arguments are filtered
     * @param pos the position of the first argument to filter
     * @param filters method handles to call initially on filtered arguments
     * @return method handle which incorporates the specified argument filtering logic
     * @throws NullPointerException if the target is null
     *                              or if the {@code filters} array is null
     * @throws IllegalArgumentException if a non-null element of {@code filters}
     *          does not match a corresponding argument type of target as described above,
     *          or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
     *          or if the resulting method handle's type would have
     *          <a href="MethodHandle.html#maxarity">too many parameters
     */
    public static
    MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
        MethodType targetType = target.type();
        MethodHandle adapter = target;
        MethodType adapterType = null;
        assert((adapterType = targetType) != null);
        int maxPos = targetType.parameterCount();
        if (pos + filters.length > maxPos)
            throw newIllegalArgumentException("too many filters");
        int curPos = pos-1;  // pre-incremented
        for (MethodHandle filter : filters) {
            curPos += 1;
            if (filter == null)  continue;  // ignore null elements of filters
            adapter = filterArgument(adapter, curPos, filter);
            assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
        }
        assert(adapterType.equals(adapter.type()));
        return adapter;
    }

    /*non-public*/ static
    MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
        MethodType targetType = target.type();
        MethodType filterType = filter.type();
        if (filterType.parameterCount() != 1
            || filterType.returnType() != targetType.parameterType(pos))
            throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
        return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
    }

    /**
     * Adapts a target method handle by pre-processing
     * a sub-sequence of its arguments with a filter (another method handle).
     * The pre-processed arguments are replaced by the result (if any) of the
     * filter function.
     * The target is then called on the modified (usually shortened) argument list.
     * <p>
     * If the filter returns a value, the target must accept that value as
     * its argument in position {@code pos}, preceded and/or followed by
     * any arguments not passed to the filter.
     * If the filter returns void, the target must accept all arguments
     * not passed to the filter.
     * No arguments are reordered, and a result returned from the filter
     * replaces (in order) the whole subsequence of arguments originally
     * passed to the adapter.
     * <p>
     * The argument types (if any) of the filter
     * replace zero or one argument types of the target, at position {@code pos},
     * in the resulting adapted method handle.
     * The return type of the filter (if any) must be identical to the
     * argument type of the target at position {@code pos}, and that target argument
     * is supplied by the return value of the filter.
     * <p>
     * In all cases, {@code pos} must be greater than or equal to zero, and
     * {@code pos} must also be less than or equal to the target's arity.
     * <p>Example:
     * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle deepToString = publicLookup()
  .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));

MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
assertEquals("[strange]", (String) ts1.invokeExact("strange"));

MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));

MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
assertEquals("[top, [up, down], strange]",
             (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));

MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
assertEquals("[top, [up, down], [strange]]",
             (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));

MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
assertEquals("[top, [[up, down, strange], charm], bottom]",
             (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
     * }</pre>
     * <p> Here is pseudocode for the resulting adapter:
     * <blockquote>
{@code
     * T target(A...,V,C...);
     * V filter(B...);
     * T adapter(A... a,B... b,C... c) {
     *   V v = filter(b...);
     *   return target(a...,v,c...);
     * }
     * // and if the filter has no arguments:
     * T target2(A...,V,C...);
     * V filter2();
     * T adapter2(A... a,C... c) {
     *   V v = filter2();
     *   return target2(a...,v,c...);
     * }
     * // and if the filter has a void return:
     * T target3(A...,C...);
     * void filter3(B...);
     * void adapter3(A... a,B... b,C... c) {
     *   filter3(b...);
     *   return target3(a...,c...);
     * }
     * }</pre>
     * <p>
     * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
     * one which first "folds" the affected arguments, and then drops them, in separate
     * steps as follows:
     * <blockquote>
{@code
     * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
     * mh = MethodHandles.foldArguments(mh, coll); //step 1
     * }</pre>
     * If the target method handle consumes no arguments besides than the result
     * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
     * is equivalent to {@code filterReturnValue(coll, mh)}.
     * If the filter method handle {@code coll} consumes one argument and produces
     * a non-void result, then {@code collectArguments(mh, N, coll)}
     * is equivalent to {@code filterArguments(mh, N, coll)}.
     * Other equivalences are possible but would require argument permutation.
     *
     * @param target the method handle to invoke after filtering the subsequence of arguments
     * @param pos the position of the first adapter argument to pass to the filter,
     *            and/or the target argument which receives the result of the filter
     * @param filter method handle to call on the subsequence of arguments
     * @return method handle which incorporates the specified argument subsequence filtering logic
     * @throws NullPointerException if either argument is null
     * @throws IllegalArgumentException if the return type of {@code filter}
     *          is non-void and is not the same as the {@code pos} argument of the target,
     *          or if {@code pos} is not between 0 and the target's arity, inclusive,
     *          or if the resulting method handle's type would have
     *          <a href="MethodHandle.html#maxarity">too many parameters
     * @see MethodHandles#foldArguments
     * @see MethodHandles#filterArguments
     * @see MethodHandles#filterReturnValue
     */
    public static
    MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
        MethodType targetType = target.type();
        MethodType filterType = filter.type();
        if (filterType.returnType() != void.class &&
            filterType.returnType() != targetType.parameterType(pos))
            throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
        return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
    }

    /**
     * Adapts a target method handle by post-processing
     * its return value (if any) with a filter (another method handle).
     * The result of the filter is returned from the adapter.
     * <p>
     * If the target returns a value, the filter must accept that value as
     * its only argument.
     * If the target returns void, the filter must accept no arguments.
     * <p>
     * The return type of the filter
     * replaces the return type of the target
     * in the resulting adapted method handle.
     * The argument type of the filter (if any) must be identical to the
     * return type of the target.
     * <p>Example:
     * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
MethodHandle length = lookup().findVirtual(String.class,
  "length", methodType(int.class));
System.out.println((String) cat.invokeExact("x", "y")); // xy
MethodHandle f0 = filterReturnValue(cat, length);
System.out.println((int) f0.invokeExact("x", "y")); // 2
     * }</pre>
     * <p> Here is pseudocode for the resulting adapter:
     * <blockquote>
{@code
     * V target(A...);
     * T filter(V);
     * T adapter(A... a) {
     *   V v = target(a...);
     *   return filter(v);
     * }
     * // and if the target has a void return:
     * void target2(A...);
     * T filter2();
     * T adapter2(A... a) {
     *   target2(a...);
     *   return filter2();
     * }
     * // and if the filter has a void return:
     * V target3(A...);
     * void filter3(V);
     * void adapter3(A... a) {
     *   V v = target3(a...);
     *   filter3(v);
     * }
     * }</pre>
     * @param target the method handle to invoke before filtering the return value
     * @param filter method handle to call on the return value
     * @return method handle which incorporates the specified return value filtering logic
     * @throws NullPointerException if either argument is null
     * @throws IllegalArgumentException if the argument list of {@code filter}
     *          does not match the return type of target as described above
     */
    public static
    MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
        MethodType targetType = target.type();
        MethodType filterType = filter.type();
        Class<?> rtype = targetType.returnType();
        int filterValues = filterType.parameterCount();
        if (filterValues == 0
                ? (rtype != void.class)
                : (rtype != filterType.parameterType(0)))
            throw newIllegalArgumentException("target and filter types do not match", target, filter);
        // result = fold( lambda(retval, arg...) { filter(retval) },
        //                lambda(        arg...) { target(arg...) } )
        return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
    }

    /**
     * Adapts a target method handle by pre-processing
     * some of its arguments, and then calling the target with
     * the result of the pre-processing, inserted into the original
     * sequence of arguments.
     * <p>
     * The pre-processing is performed by {@code combiner}, a second method handle.
     * Of the arguments passed to the adapter, the first {@code N} arguments
     * are copied to the combiner, which is then called.
     * (Here, {@code N} is defined as the parameter count of the combiner.)
     * After this, control passes to the target, with any result
     * from the combiner inserted before the original {@code N} incoming
     * arguments.
     * <p>
     * If the combiner returns a value, the first parameter type of the target
     * must be identical with the return type of the combiner, and the next
     * {@code N} parameter types of the target must exactly match the parameters
     * of the combiner.
     * <p>
     * If the combiner has a void return, no result will be inserted,
     * and the first {@code N} parameter types of the target
     * must exactly match the parameters of the combiner.
     * <p>
     * The resulting adapter is the same type as the target, except that the
     * first parameter type is dropped,
     * if it corresponds to the result of the combiner.
     * <p>
     * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
     * that either the combiner or the target does not wish to receive.
     * If some of the incoming arguments are destined only for the combiner,
     * consider using {@link MethodHandle#asCollector asCollector} instead, since those
     * arguments will not need to be live on the stack on entry to the
     * target.)
     * <p>Example:
     * <blockquote>
{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
  "println", methodType(void.class, String.class))
    .bindTo(System.out);
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
MethodHandle catTrace = foldArguments(cat, trace);
// also prints "boo":
assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
     * }</pre>
     * <p> Here is pseudocode for the resulting adapter:
     * <blockquote>
{@code
     * // there are N arguments in A...
     * T target(V, A[N]..., B...);
     * V combiner(A...);
     * T adapter(A... a, B... b) {
     *   V v = combiner(a...);
     *   return target(v, a..., b...);
     * }
     * // and if the combiner has a void return:
     * T target2(A[N]..., B...);
     * void combiner2(A...);
     * T adapter2(A... a, B... b) {
     *   combiner2(a...);
     *   return target2(a..., b...);
     * }
     * }</pre>
     * @param target the method handle to invoke after arguments are combined
     * @param combiner method handle to call initially on the incoming arguments
     * @return method handle which incorporates the specified argument folding logic
     * @throws NullPointerException if either argument is null
     * @throws IllegalArgumentException if {@code combiner}'s return type
     *          is non-void and not the same as the first argument type of
     *          the target, or if the initial {@code N} argument types
     *          of the target
     *          (skipping one matching the {@code combiner}'s return type)
     *          are not identical with the argument types of {@code combiner}
     */
    public static
    MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
        int pos = 0;
        MethodType targetType = target.type();
        MethodType combinerType = combiner.type();
        int foldPos = pos;
        int foldArgs = combinerType.parameterCount();
        int foldVals = combinerType.returnType() == void.class ? 0 : 1;
        int afterInsertPos = foldPos + foldVals;
        boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
        if (ok && !(combinerType.parameterList()
                    .equals(targetType.parameterList().subList(afterInsertPos,
                                                               afterInsertPos + foldArgs))))
            ok = false;
        if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
            ok = false;
        if (!ok)
            throw misMatchedTypes("target and combiner types", targetType, combinerType);
        MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
        return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
    }

    /**
     * Makes a method handle which adapts a target method handle,
     * by guarding it with a test, a boolean-valued method handle.
     * If the guard fails, a fallback handle is called instead.
     * All three method handles must have the same corresponding
     * argument and return types, except that the return type
     * of the test must be boolean, and the test is allowed
     * to have fewer arguments than the other two method handles.
     * <p> Here is pseudocode for the resulting adapter:
     * <blockquote>
{@code
     * boolean test(A...);
     * T target(A...,B...);
     * T fallback(A...,B...);
     * T adapter(A... a,B... b) {
     *   if (test(a...))
     *     return target(a..., b...);
     *   else
     *     return fallback(a..., b...);
     * }
     * }</pre>
     * Note that the test arguments ({@code a...} in the pseudocode) cannot
     * be modified by execution of the test, and so are passed unchanged
     * from the caller to the target or fallback as appropriate.
     * @param test method handle used for test, must return boolean
     * @param target method handle to call if test passes
     * @param fallback method handle to call if test fails
     * @return method handle which incorporates the specified if/then/else logic
     * @throws NullPointerException if any argument is null
     * @throws IllegalArgumentException if {@code test} does not return boolean,
     *          or if all three method types do not match (with the return
     *          type of {@code test} changed to match that of the target).
     */
    public static
    MethodHandle guardWithTest(MethodHandle test,
                               MethodHandle target,
                               MethodHandle fallback) {
        MethodType gtype = test.type();
        MethodType ttype = target.type();
        MethodType ftype = fallback.type();
        if (!ttype.equals(ftype))
            throw misMatchedTypes("target and fallback types", ttype, ftype);
        if (gtype.returnType() != boolean.class)
            throw newIllegalArgumentException("guard type is not a predicate "+gtype);
        List<Class targs = ttype.parameterList();
        List<Class gargs = gtype.parameterList();
        if (!targs.equals(gargs)) {
            int gpc = gargs.size(), tpc = targs.size();
            if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
                throw misMatchedTypes("target and test types", ttype, gtype);
            test = dropArguments(test, gpc, targs.subList(gpc, tpc));
            gtype = test.type();
        }
        return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
    }

    static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
        return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
    }

    /**
     * Makes a method handle which adapts a target method handle,
     * by running it inside an exception handler.
     * If the target returns normally, the adapter returns that value.
     * If an exception matching the specified type is thrown, the fallback
     * handle is called instead on the exception, plus the original arguments.
     * <p>
     * The target and handler must have the same corresponding
     * argument and return types, except that handler may omit trailing arguments
     * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
     * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
     * <p> Here is pseudocode for the resulting adapter:
     * <blockquote>
{@code
     * T target(A..., B...);
     * T handler(ExType, A...);
     * T adapter(A... a, B... b) {
     *   try {
     *     return target(a..., b...);
     *   } catch (ExType ex) {
     *     return handler(ex, a...);
     *   }
     * }
     * }</pre>
     * Note that the saved arguments ({@code a...} in the pseudocode) cannot
     * be modified by execution of the target, and so are passed unchanged
     * from the caller to the handler, if the handler is invoked.
     * <p>
     * The target and handler must return the same type, even if the handler
     * always throws.  (This might happen, for instance, because the handler
     * is simulating a {@code finally} clause).
     * To create such a throwing handler, compose the handler creation logic
     * with {@link #throwException throwException},
     * in order to create a method handle of the correct return type.
     * @param target method handle to call
     * @param exType the type of exception which the handler will catch
     * @param handler method handle to call if a matching exception is thrown
     * @return method handle which incorporates the specified try/catch logic
     * @throws NullPointerException if any argument is null
     * @throws IllegalArgumentException if {@code handler} does not accept
     *          the given exception type, or if the method handle types do
     *          not match in their return types and their
     *          corresponding parameters
     */
    public static
    MethodHandle catchException(MethodHandle target,
                                Class<? extends Throwable> exType,
                                MethodHandle handler) {
        MethodType ttype = target.type();
        MethodType htype = handler.type();
        if (htype.parameterCount() < 1 ||
            !htype.parameterType(0).isAssignableFrom(exType))
            throw newIllegalArgumentException("handler does not accept exception type "+exType);
        if (htype.returnType() != ttype.returnType())
            throw misMatchedTypes("target and handler return types", ttype, htype);
        List<Class targs = ttype.parameterList();
        List<Class hargs = htype.parameterList();
        hargs = hargs.subList(1, hargs.size());  // omit leading parameter from handler
        if (!targs.equals(hargs)) {
            int hpc = hargs.size(), tpc = targs.size();
            if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
                throw misMatchedTypes("target and handler types", ttype, htype);
            handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
            htype = handler.type();
        }
        return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
    }

    /**
     * Produces a method handle which will throw exceptions of the given {@code exType}.
     * The method handle will accept a single argument of {@code exType},
     * and immediately throw it as an exception.
     * The method type will nominally specify a return of {@code returnType}.
     * The return type may be anything convenient:  It doesn't matter to the
     * method handle's behavior, since it will never return normally.
     * @param returnType the return type of the desired method handle
     * @param exType the parameter type of the desired method handle
     * @return method handle which can throw the given exceptions
     * @throws NullPointerException if either argument is null
     */
    public static
    MethodHandle throwException(Class<?> returnType, Class exType) {
        if (!Throwable.class.isAssignableFrom(exType))
            throw new ClassCastException(exType.getName());
        return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
    }
}


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