BufferedReader reflection : Class Loader « Reflection « Java Tutorial

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import static java.lang.System.out;

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;

public class GrowBufferedReader {
  private static final int srcBufSize = 10 * 1024;
  private static char[] src = new char[srcBufSize];
  static {
    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();
    }
  }
}