Wednesday, 7 November 2012

A Binary Chop Java method to discover memory limits

If you want to discover exactly how many Objects you can store in your JVM with its current memory configuration this little functional style method might help.

  public void testChop() { 
    // -Xmx=256m
    //assertEquals(33554433, between(1, Integer.MAX_VALUE));
    // -Xmx=1966m
      assertEquals(343535293, between(1, Integer.MAX_VALUE));
  public int between(int from, int to) {
    if ((to - from) <= 1) 
      return (to);
    int i = from + ((to - from) /2);
    try { 
      Object[] a = new Object[i];
      return (between(i, to));
    } catch (OutOfMemoryError e) {
      return (between(from, i));

Another thing to note is the speed that this runs at: memory allocation can be very slow.

Obviously, in hindsight, this routine will always take 30 steps.

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