Question

How can we find out missing elements from two arrays ?
Ex:

        int []array1 ={1,2,3,4,5};           
        int []array2 ={3,1,2};

From the above two arrays i want to find what are the missing elements in second array?

Answer 1

Convert them to Sets and use removeAll.

The first problem is how to convert a primitive int[] to a collection.
With Guava you can use:

List<Integer> list1 = Ints.asList(array1);
List<Integer> list2 = Ints.asList(array2);

Apache commons (which I’m not familiar with) apparently has something similar.

Now convert to a set:

Set<Integer> set1 = new HashSet<Integer>(list1);

And compute the difference:

set1.removeAll(list2);

And convert the result back to an array:

return Ints.toArray(set1);