I have a 2010 iMac with 8GB of RAM, running Eclipse Neon.2 Release (4.6.2) with Java 1.8.0_25. With the VM argument -Xmx6g, I ran the following code:
StringBuilder sb = new StringBuilder();
for (int i = 0; i < Integer.MAX_VALUE; i++) {
try {
sb.append('a');
} catch (Throwable e) {
System.out.println(i);
break;
}
}
System.out.println(sb.toString().length());
This prints:
Requested array size exceeds VM limit
1207959550
So, it seems that the max array size is ~1,207,959,549. Then I realized that we don't actually care if Java runs out of memory: we're just looking for the maximum array size (which seems to be a constant defined somewhere). So:
for (int i = 0; i < 1_000; i++) {
try {
char[] array = new char[Integer.MAX_VALUE - i];
Arrays.fill(array, 'a');
String string = new String(array);
System.out.println(string.length());
} catch (Throwable e) {
System.out.println(e.getMessage());
System.out.println("Last: " + (Integer.MAX_VALUE - i));
System.out.println("Last: " + i);
}
}
Which prints:
Requested array size exceeds VM limit
Last: 2147483647
Last: 0
Requested array size exceeds VM limit
Last: 2147483646
Last: 1
Java heap space
Last: 2147483645
Last: 2
So, it seems the max is Integer.MAX_VALUE - 2, or (2^31) - 3
P.S. I'm not sure why my StringBuilder maxed out at 1207959550 while my char[] maxed out at (2^31)-3. It seems that AbstractStringBuilder doubles the size of its internal char[] to grow it, so that probably causes the issue.