Do Java arrays have a maximum size?

Is there a limit to the number of elements a Java array can contain? If so, what is it?

Haven't seen the right answer, even though it's very easy to test.

In a recent HotSpot VM, the correct answer is Integer.MAX_VALUE - 5. Once you go beyond that:

public class Foo {
  public static void main(String[] args) {
    Object[] array = new Object[Integer.MAX_VALUE - 4];
  }
}

You get:

Exception in thread "main" java.lang.OutOfMemoryError:
  Requested array size exceeds VM limit

This is (of course) totally VM-dependent.

Browsing through the source code of OpenJDK 7 and 8 java.util.ArrayList, .Hashtable, .AbstractCollection, .PriorityQueue, and .Vector, you can see this claim being repeated:

/**
 * Some VMs reserve some header words in an array.
 * Attempts to allocate larger arrays may result in
 * OutOfMemoryError: Requested array size exceeds VM limit
 */
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

which is added by Martin Buchholz (Google) on 2010-05-09; reviewed by Chris Hegarty (Oracle).

So, probably we can say that the maximum "safe" number would be 2 147 483 639 (Integer.MAX_VALUE - 8) and "attempts to allocate larger arrays may result in OutOfMemoryError".

(Yes, Buchholz's standalone claim does not include backing evidence, so this is a calculated appeal to authority. Even within OpenJDK itself, we can see code like return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE; which shows that MAX_ARRAY_SIZE does not yet have a real use.)

There are actually two limits. One, the maximum element indexable for the array and, two, the amount of memory available to your application. Depending on the amount of memory available and the amount used by other data structures, you may hit the memory limit before you reach the maximum addressable array element.