How is ArrayOutOfBoundsException possible in String.valueOf(int)?

Question

Why does this code sometimes produce ArrayOutOfBoundsException? How is that even possible for String.valueOf(int)?

public static String ipToString(B         


        

Answer 1

I can reliably reproduce your issue with this code:

public class Main
{
  public static StringBuilder intToString(byte[] bs) {
    final StringBuilder sb = new StringBuilder();
    boolean started = false;
    for (Byte byt : bs) {
      if (started) sb.append(".");
      sb.append(String.valueOf(byt & 0xFF));
      started = true;
    }
    return sb;
  }

  public static void main(String[] args) {
    final byte[] bs = {-2, -1, 0, 1, 2};
    while (true) intToString(bs);
  }
}

The issue will almost certainly be traced to a JIT compiler bug. Your observation that, once it happens the first time, it happens reliably on every subsequent call, points cleanly to a JIT compilation event which introduces the buggy code into the codepath.

If that's available to you, you could activate diagnostic JVM options which will print all compilation events (-XX:PrintCompilation). Then you may be able to correlate such an event with the moment when the exception starts appearing.