Java example source code file (Reflect.java)

This example Java source code file (Reflect.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

accessibleobject, class, classnotfoundexception, constructor, field, illegalaccessexception, invocationtargetexception, ioexception, nosuchmethodexception, object, privilegedaction, reflection, reflectionerror, security, string, void

The Reflect.java Java example source code

/*
 * Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.nio.ch;

import java.io.*;
import java.lang.reflect.*;
import java.security.AccessController;
import java.security.PrivilegedAction;


class Reflect {                                 // package-private

    private Reflect() { }

    private static class ReflectionError extends Error {
        private static final long serialVersionUID = -8659519328078164097L;
        ReflectionError(Throwable x) {
            super(x);
        }
    }

    private static void setAccessible(final AccessibleObject ao) {
        AccessController.doPrivileged(new PrivilegedAction<Void>() {
                public Void run() {
                    ao.setAccessible(true);
                    return null;
                }});
    }

    static Constructor<?> lookupConstructor(String className,
                                            Class<?>[] paramTypes)
    {
        try {
            Class<?> cl = Class.forName(className);
            Constructor<?> c = cl.getDeclaredConstructor(paramTypes);
            setAccessible(c);
            return c;
        } catch (ClassNotFoundException | NoSuchMethodException x) {
            throw new ReflectionError(x);
        }
    }

    static Object invoke(Constructor<?> c, Object[] args) {
        try {
            return c.newInstance(args);
        } catch (InstantiationException |
                 IllegalAccessException |
                 InvocationTargetException x) {
            throw new ReflectionError(x);
        }
    }

    static Method lookupMethod(String className,
                               String methodName,
                               Class... paramTypes)
    {
        try {
            Class<?> cl = Class.forName(className);
            Method m = cl.getDeclaredMethod(methodName, paramTypes);
            setAccessible(m);
            return m;
        } catch (ClassNotFoundException | NoSuchMethodException x) {
            throw new ReflectionError(x);
        }
    }

    static Object invoke(Method m, Object ob, Object[] args) {
        try {
            return m.invoke(ob, args);
        } catch (IllegalAccessException | InvocationTargetException x) {
            throw new ReflectionError(x);
        }
    }

    static Object invokeIO(Method m, Object ob, Object[] args)
        throws IOException
    {
        try {
            return m.invoke(ob, args);
        } catch (IllegalAccessException x) {
            throw new ReflectionError(x);
        } catch (InvocationTargetException x) {
            if (IOException.class.isInstance(x.getCause()))
                throw (IOException)x.getCause();
            throw new ReflectionError(x);
        }
    }

    static Field lookupField(String className, String fieldName) {
        try {
            Class<?> cl = Class.forName(className);
            Field f = cl.getDeclaredField(fieldName);
            setAccessible(f);
            return f;
        } catch (ClassNotFoundException | NoSuchFieldException x) {
            throw new ReflectionError(x);
        }
    }

    static Object get(Object ob, Field f) {
        try {
            return f.get(ob);
        } catch (IllegalAccessException x) {
            throw new ReflectionError(x);
        }
    }

    static Object get(Field f) {
        return get(null, f);
    }

    static void set(Object ob, Field f, Object val) {
        try {
            f.set(ob, val);
        } catch (IllegalAccessException x) {
            throw new ReflectionError(x);
        }
    }

    static void setInt(Object ob, Field f, int val) {
        try {
            f.setInt(ob, val);
        } catch (IllegalAccessException x) {
            throw new ReflectionError(x);
        }
    }

    static void setBoolean(Object ob, Field f, boolean val) {
        try {
            f.setBoolean(ob, val);
        } catch (IllegalAccessException x) {
            throw new ReflectionError(x);
        }
    }

}