Thanks for your reply. I added the -Xmx3g command to the vm command-line options in NetBeans and it ran successfully.

What I don’t get is that the default runtime heap is 64m. It requires 3,000m, so the 100e6 array of Integers requires 2,936m which is equivalent to ~29bytes per element. With each int requiring 4bytes do you know why it requires ~29bytes per element?

I noticed when compiling your sequential MergeSort that I get unchecked call warnings on all of the calls to compareTo(). I also noticed that you use Comparable without using generics although Comparable is a generic type. Thus, I rewrote the MergeSort class to have declaration:

public class MergeSort<T extends Comparable>
{
//…

The static method syntax does support generics but the syntax gets very messy so I decided to add type T to the class.

I replaced every instance of “Comparable” with “T”.

The only difficulty arose in method sort() with:

Comparable[] tmp = new Comparable[((hi - lo) / 2) + 1];

having to be replaced by:

T[] tmp = (T[])Array.newInstance(a.getClass().getComponentType(), ((hi – lo) / 2) + 1);

which is still an unchecked cast! And required:

@SuppressWarnings(“unchecked”)

before the method declaration.

Thus, it would appear that there is no escape from the unchecked call/cast!!

Graham

I did some experimentation, and it looks like you’ll need to let the Java heap grow to about 3GB. This can be done with the command line option: -Xmx3072M.

After doing that, it was able to finish allocating all of the integers.

I implemented your sequential merge sort and setup a test that fills an array with random numbers:

int size = (int)1e8;
Integer[] iarray = new Integer[size];
RandomNumber rn = new RandomNumber();
for (int i=0; i<size; i++)
{
int number = (int)rn.numberInRange(0,size);
iarray[i] = new Integer(number);
}

The random number generator is my own and simply returns a random number within a range.

With the shown size of 1e08 for the array length I get the following exception:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at hedgehog_samples.utility.MergeSortSample.main(MergeSortSample.java:44)

I was wondering how you would perform such a test? Do I need to allocate a runtime parameter to allocate a larger block of memory?

If I set the array size to 1e06 then it performs the sort almost immediately and hence to perform a proper test of this sort I need to have much larger array lengths.

Thanks.