Java example source code file (ObjectReference.java)
The ObjectReference.java Java example source code
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* accompanied this code).
*
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package com.sun.jdi;
import java.util.List;
import java.util.Map;
/**
* An object that currently exists in the target VM. An ObjectReference
* mirrors only the object itself and is not specific to any
* {@link Field} or {@link LocalVariable} to which it is currently
* assigned. An ObjectReference can
* have 0 or more references from field(s) and/or variable(s).
* <p>
* Any method on <code>ObjectReference which directly or
* indirectly takes <code>ObjectReference as an parameter may throw
* {@link com.sun.jdi.VMDisconnectedException} if the target VM is
* disconnected and the {@link com.sun.jdi.event.VMDisconnectEvent} has been or is
* available to be read from the {@link com.sun.jdi.event.EventQueue}.
* <p>
* Any method on <code>ObjectReference which directly or
* indirectly takes <code>ObjectReference as an parameter may throw
* {@link com.sun.jdi.VMOutOfMemoryException} if the target VM has run out of memory.
* <p>
* Any method on <code>ObjectReference or which directly or indirectly takes
* <code>ObjectReference as parameter may throw
* {@link com.sun.jdi.ObjectCollectedException} if the mirrored object has been
* garbage collected.
*
* @author Robert Field
* @author Gordon Hirsch
* @author James McIlree
* @since 1.3
*/
@jdk.Exported
public interface ObjectReference extends Value {
/**
* Gets the {@link ReferenceType} that mirrors the type
* of this object. The type may be a subclass or implementor of the
* declared type of any field or variable which currently holds it.
* For example, right after the following statement.
* <p>
* <code>Object obj = new String("Hello, world!");
* <p>
* The ReferenceType of obj will mirror java.lang.String and not
* java.lang.Object.
* <p>
* The type of an object never changes, so this method will
* always return the same ReferenceType over the lifetime of the
* mirrored object.
* <p>
* The returned ReferenceType will be a {@link ClassType} or
* {@link ArrayType} and never an {@link InterfaceType}.
*
* @return the {@link ReferenceType} for this object.
*/
ReferenceType referenceType();
/**
* Gets the value of a given instance or static field in this object.
* The Field must be valid for this ObjectReference;
* that is, it must be from
* the mirrored object's class or a superclass of that class.
*
* @param sig the field containing the requested value
* @return the {@link Value} of the instance field.
* @throws java.lang.IllegalArgumentException if the field is not valid for
* this object's class.
*/
Value getValue(Field sig);
/**
* Gets the value of multiple instance and/or static fields in this object.
* The Fields must be valid for this ObjectReference;
* that is, they must be from
* the mirrored object's class or a superclass of that class.
*
* @param fields a list of {@link Field} objects containing the
* requested values.
* @return a Map of the requested {@link Field} objects with
* their {@link Value}.
* @throws java.lang.IllegalArgumentException if any field is not valid for
* this object's class.
*/
Map<Field,Value> getValues(List fields);
/**
* Sets the value of a given instance or static field in this object.
* The {@link Field} must be valid for this ObjectReference; that is,
* it must be from the mirrored object's class or a superclass of that class.
* If static, the field must not be final.
* <p>
* Object values must be assignment compatible with the field type
* (This implies that the field type must be loaded through the
* enclosing class's class loader). Primitive values must be
* either assignment compatible with the field type or must be
* convertible to the field type without loss of information.
* See section 5.2 of
* <cite>The Java™ Language Specification
* for more information on assignment
* compatibility.
*
* @param field the field containing the requested value
* @param value the new value to assign
* @throws java.lang.IllegalArgumentException if the field is not valid for
* this object's class.
* @throws InvalidTypeException if the value's type does not match
* the field's type.
* @throws ClassNotLoadedException if 'value' is not null, and the field
* type has not yet been loaded through the appropriate class loader.
* @throws VMCannotBeModifiedException if the VirtualMachine is read-only - see {@link VirtualMachine#canBeModified()}.
*/
void setValue(Field field, Value value)
throws InvalidTypeException, ClassNotLoadedException;
/** Perform method invocation with only the invoking thread resumed */
static final int INVOKE_SINGLE_THREADED = 0x1;
/** Perform non-virtual method invocation */
static final int INVOKE_NONVIRTUAL = 0x2;
/**
* Invokes the specified {@link Method} on this object in the
* target VM. The
* specified method can be defined in this object's class,
* in a superclass of this object's class, or in an interface
* implemented by this object. The method may be a static method
* or an instance method, but not a static initializer or constructor.
* Use {@link ClassType#newInstance} to create a new object and
* run its constructor.
* <p>
* The method invocation will occur in the specified thread.
* Method invocation can occur only if the specified thread
* has been suspended by an event which occurred in that thread.
* Method invocation is not supported
* when the target VM has been suspended through
* {@link VirtualMachine#suspend} or when the specified thread
* is suspended through {@link ThreadReference#suspend}.
* <p>
* The specified method is invoked with the arguments in the specified
* argument list. The method invocation is synchronous; this method
* does not return until the invoked method returns in the target VM.
* If the invoked method throws an exception, this method
* will throw an {@link InvocationException} which contains
* a mirror to the exception object thrown.
* <p>
* Object arguments must be assignment compatible with the argument type
* (This implies that the argument type must be loaded through the
* enclosing class's class loader). Primitive arguments must be
* either assignment compatible with the argument type or must be
* convertible to the argument type without loss of information.
* If the method being called accepts a variable number of arguments,
* then the last argument type is an array of some component type.
* The argument in the matching position can be omitted, or can be null,
* an array of the same component type, or an argument of the
* component type followed by any number of other arguments of the same
* type. If the argument is omitted, then a 0 length array of the
* component type is passed. The component type can be a primitive type.
* Autoboxing is not supported.
*
* See section 5.2 of
* <cite>The Java™ Language Specification
* for more information on assignment compatibility.
* <p>
* By default, the method is invoked using dynamic lookup as
* documented in section 15.12.4.4 of
* <cite>The Java™ Language Specification
* in particular, overriding based on the runtime type of the object
* mirrored by this {@link ObjectReference} will occur. This
* behavior can be changed by specifying the
* {@link #INVOKE_NONVIRTUAL} bit flag in the <code>options
* argument. If this flag is set, the specified method is invoked
* whether or not it is overridden for this object's runtime type.
* The method, in this case, must not belong to an interface and
* must not be abstract. This option is useful for performing method
* invocations like those done with the <code>super keyword in
* the Java programming language.
* <p>
* By default, all threads in the target VM are resumed while
* the method is being invoked if they were previously
* suspended by an event or by {@link VirtualMachine#suspend} or
* {@link ThreadReference#suspend}. This is done to prevent the deadlocks
* that will occur if any of the threads own monitors
* that will be needed by the invoked method.
* Note, however, that this implicit resume acts exactly like
* {@link ThreadReference#resume}, so if the thread's suspend
* count is greater than 1, it will remain in a suspended state
* during the invocation and thus a deadlock could still occur.
* By default, when the invocation completes,
* all threads in the target VM are suspended, regardless their state
* before the invocation.
* It is possible that
* breakpoints or other events might occur during the invocation.
* This can cause deadlocks as described above. It can also cause a deadlock
* if invokeMethod is called from the client's event handler thread. In this
* case, this thread will be waiting for the invokeMethod to complete and
* won't read the EventSet that comes in for the new event. If this
* new EventSet is SUSPEND_ALL, then a deadlock will occur because no
* one will resume the EventSet. To avoid this, all EventRequests should
* be disabled before doing the invokeMethod, or the invokeMethod should
* not be done from the client's event handler thread.
* <p>
* The resumption of other threads during the invocation can be prevented
* by specifying the {@link #INVOKE_SINGLE_THREADED}
* bit flag in the <code>options argument; however,
* there is no protection against or recovery from the deadlocks
* described above, so this option should be used with great caution.
* Only the specified thread will be resumed (as described for all
* threads above). Upon completion of a single threaded invoke, the invoking thread
* will be suspended once again. Note that any threads started during
* the single threaded invocation will not be suspended when the
* invocation completes.
* <p>
* If the target VM is disconnected during the invoke (for example, through
* {@link VirtualMachine#dispose}) the method invocation continues.
*
* @param thread the thread in which to invoke.
* @param method the {@link Method} to invoke.
* @param arguments the list of {@link Value} arguments bound to the
* invoked method. Values from the list are assigned to arguments
* in the order they appear in the method signature.
* @param options the integer bit flag options.
* @return a {@link Value} mirror of the invoked method's return value.
* @throws java.lang.IllegalArgumentException if the method is not
* a member of this object's class, if the size of the argument list
* does not match the number of declared arguemnts for the method,
* if the method is a constructor or static intializer, or
* if {@link #INVOKE_NONVIRTUAL} is specified and the method is
* either abstract or an interface member.
* @throws {@link InvalidTypeException} if any argument in the
* argument list is not assignable to the corresponding method argument
* type.
* @throws ClassNotLoadedException if any argument type has not yet been loaded
* through the appropriate class loader.
* @throws IncompatibleThreadStateException if the specified thread has not
* been suspended by an event.
* @throws InvocationException if the method invocation resulted in
* an exception in the target VM.
* @throws InvalidTypeException If the arguments do not meet this requirement --
* Object arguments must be assignment compatible with the argument
* type. This implies that the argument type must be
* loaded through the enclosing class's class loader.
* Primitive arguments must be either assignment compatible with the
* argument type or must be convertible to the argument type without loss
* of information. See JLS section 5.2 for more information on assignment
* compatibility.
* @throws VMCannotBeModifiedException if the VirtualMachine is read-only - see {@link VirtualMachine#canBeModified()}.
*/
Value invokeMethod(ThreadReference thread, Method method,
List<? extends Value> arguments, int options)
throws InvalidTypeException,
ClassNotLoadedException,
IncompatibleThreadStateException,
InvocationException;
/**
* Prevents garbage collection for this object. By default all
* {@link ObjectReference} values returned by JDI may be collected
* at any time the target VM is running. A call to this method
* guarantees that the object will not be collected.
* {@link #enableCollection} can be used to allow collection once
* again.
* <p>
* Calls to this method are counted. Every call to this method
* requires a corresponding call to {@link #enableCollection} before
* garbage collection is re-enabled.
* <p>
* Note that while the target VM is suspended, no garbage collection
* will occur because all threads are suspended. The typical
* examination of variables, fields, and arrays during the suspension
* is safe without explicitly disabling garbage collection.
* <p>
* This method should be used sparingly, as it alters the
* pattern of garbage collection in the target VM and,
* consequently, may result in application behavior under the
* debugger that differs from its non-debugged behavior.
* @throws VMCannotBeModifiedException if the VirtualMachine is read-only
* -see {@link VirtualMachine#canBeModified()}.
*/
void disableCollection();
/**
* Permits garbage collection for this object. By default all
* {@link ObjectReference} values returned by JDI may be collected
* at any time the target VM is running. A call to this method
* is necessary only if garbage collection was previously disabled
* with {@link #disableCollection}.
* @throws VMCannotBeModifiedException if the VirtualMachine is read-only
* -see {@link VirtualMachine#canBeModified()}.
*/
void enableCollection();
/**
* Determines if this object has been garbage collected in the target
* VM.
*
* @return <code>true if this {@link ObjectReference} has been collected;
* <code>false otherwise.
* @throws VMCannotBeModifiedException if the VirtualMachine is read-only
* -see {@link VirtualMachine#canBeModified()}.
*/
boolean isCollected();
/**
* Returns a unique identifier for this ObjectReference.
* It is guaranteed to be unique among all
* ObjectReferences from the same VM that have not yet been disposed.
* The guarantee applies as long
* as this ObjectReference has not yet been disposed.
*
* @return a long unique ID
*/
long uniqueID();
/**
* Returns a List containing a {@link ThreadReference} for
* each thread currently waiting for this object's monitor.
* See {@link ThreadReference#currentContendedMonitor} for
* information about when a thread is considered to be waiting
* for a monitor.
* <p>
* Not all target VMs support this operation. See
* VirtualMachine#canGetMonitorInfo to determine if the
* operation is supported.
*
* @return a List of {@link ThreadReference} objects. The list
* has zero length if no threads are waiting for the monitor.
* @throws java.lang.UnsupportedOperationException if the
* target VM does not support this operation.
* @throws IncompatibleThreadStateException if any
* waiting thread is not suspended
* in the target VM
*/
List<ThreadReference> waitingThreads()
throws IncompatibleThreadStateException;
/**
* Returns an {@link ThreadReference} for the thread, if any,
* which currently owns this object's monitor.
* See {@link ThreadReference#ownedMonitors} for a definition
* of ownership.
* <p>
* Not all target VMs support this operation. See
* VirtualMachine#canGetMonitorInfo to determine if the
* operation is supported.
*
* @return the {@link ThreadReference} which currently owns the
* monitor, or null if it is unowned.
*
* @throws java.lang.UnsupportedOperationException if the
* target VM does not support this operation.
* @throws IncompatibleThreadStateException if the owning thread is
* not suspended in the target VM
*/
ThreadReference owningThread() throws IncompatibleThreadStateException;
/**
* Returns the number times this object's monitor has been
* entered by the current owning thread.
* See {@link ThreadReference#ownedMonitors} for a definition
* of ownership.
* <p>
* Not all target VMs support this operation. See
* VirtualMachine#canGetMonitorInfo to determine if the
* operation is supported.
*
* @see #owningThread
* @return the integer count of the number of entries.
*
* @throws java.lang.UnsupportedOperationException if the
* target VM does not support this operation.
* @throws IncompatibleThreadStateException if the owning thread is
* not suspended in the target VM
*/
int entryCount() throws IncompatibleThreadStateException;
/**
* Returns objects that directly reference this object.
* Only objects that are reachable for the purposes of garbage collection
* are returned. Note that an object can also be referenced in other ways,
* such as from a local variable in a stack frame, or from a JNI global
* reference. Such non-object referrers are not returned by this method.
* <p>
* Not all target virtual machines support this operation.
* Use {@link VirtualMachine#canGetInstanceInfo()}
* to determine if the operation is supported.
*
* @see VirtualMachine#instanceCounts(List)
* @see ReferenceType#instances(long)
* @param maxReferrers The maximum number of referring objects to return.
* Must be non-negative. If zero, all referring
* objects are returned.
* @return a of List of {@link ObjectReference} objects. If there are
* no objects that reference this object, a zero-length list is returned..
* @throws java.lang.UnsupportedOperationException if
* the target virtual machine does not support this
* operation - see
* {@link VirtualMachine#canGetInstanceInfo() canGetInstanceInfo()}
* @throws java.lang.IllegalArgumentException if maxReferrers is less
* than zero.
* @since 1.6
*/
List<ObjectReference> referringObjects(long maxReferrers);
/**
* Compares the specified Object with this ObjectReference for equality.
*
* @return true if the Object is an ObjectReference, if the
* ObjectReferences belong to the same VM, and if applying the
* "==" operator on the mirrored objects in that VM evaluates to true.
*/
boolean equals(Object obj);
/**
* Returns the hash code value for this ObjectReference.
*
* @return the integer hash code
*/
int hashCode();
}
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