Grow array size with reflection - Java Reflection

Java examples for Reflection:Array

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Description

Grow array size with reflection

Demo Code

import java.io.BufferedReader;
import java.io.CharArrayReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.lang.reflect.Field;
import java.util.Arrays;
import static java.lang.System.out;

public class GrowBufferedReader {
    private static final int srcBufSize = 10 * 1024;
    private static char[] src = new char[srcBufSize];
    static {/*  w  w w. j  a v a 2 s  .  c o  m*/
        src[srcBufSize - 1] = 'x';
    }
    private static CharArrayReader car = new CharArrayReader(src);

    public static void main(String... args) {
        try {
            BufferedReader br = new BufferedReader(car);

            Class<?> c = br.getClass();
            Field f = c.getDeclaredField("cb");

            // cb is a private field
            f.setAccessible(true);
            char[] cbVal = char[].class.cast(f.get(br));

            char[] newVal = Arrays.copyOf(cbVal, cbVal.length * 2);
            if (args.length > 0 && args[0].equals("grow"))
                f.set(br, newVal);

            for (int i = 0; i < srcBufSize; i++)
                br.read();

            // see if the new backing array is being used
            if (newVal[srcBufSize - 1] == src[srcBufSize - 1])
                out.format("Using new backing array, size=%d%n",
                        newVal.length);
            else
                out.format("Using original backing array, size=%d%n",
                        cbVal.length);

            // production code should handle these exceptions more gracefully
        } catch (FileNotFoundException x) {
            x.printStackTrace();
        } catch (NoSuchFieldException x) {
            x.printStackTrace();
        } catch (IllegalAccessException x) {
            x.printStackTrace();
        } catch (IOException x) {
            x.printStackTrace();
        }
    }
}

/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

Result


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