java.lang.OutOfMemoryError: Java heap space for java 8

Question

I use Java 8 (In Eclipse) when I got this error:

java.lang.OutOfMemoryError: Java heap space

I've tried the -Xmx command but no use even changing the MetaspaceSize doesn't solve it. This problem occurs when I tried to swap elements of list (it size<= 395).

public void permutation(double[] arr, int pos, ArrayList<double[]> list) {
    if (arr.length - pos == 1)
        list.add(arr.clone());
    else
        for (int i = pos; i < arr.length; i++) {
            swap(arr, pos, i);
            permutation(arr, pos + 1, list);
            swap(arr, pos, i);
        }
}

StuPointerException · Accepted Answer · 2015-04-28 18:08:44Z

2

Changing the amount of heap space you are allocating won't solve the problem.

Your heap is being used up because you are creating an incredible number of objects and looking at what you are trying to achieve, this is likely a bug in your code.

You need to debug your application to determine where all of the objects are being created and why the garbage collector can't clear them up.

answered Apr 28, 2015 at 18:08

StuPointerException

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Peter Lawrey · Accepted Answer · 2015-04-29 11:12:10Z

Instead of building a List of every possible combination will use a lot of memory and when exploring combinations the number of results can grow exponentially with the number of elements you input.

A simple way around this it to provide a call back to process each combination as it happens. This will leave the amount of work much the same, but the memory consumption drops from O(x^n) to O(1)

public void permutation(double[] arr, int pos, Consumer<double[]> consumer) {
    if (arr.length - pos == 1)
        consumer.accept(arr);
    else
        for (int i = pos; i < arr.length; i++) {
            swap(arr, pos, i);
            permutation(arr, pos + 1, list);
            swap(arr, pos, i);
        }
}

Note: you can create a consumer which adds clones to a List, but you can also print or process the results as you go.

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