java - Common elements in two lists

Question

I have two ArrayList objects with three integers each. I want to find a way to return the common elements of the two lists. Has anybody an idea how I can achieve this?

Answer 1

Use Collection#retainAll().

listA.retainAll(listB);
// listA now contains only the elements which are also contained in listB.

If you want to avoid that changes are being affected in listA, then you need to create a new one.

List<Integer> common = new ArrayList<Integer>(listA);
common.retainAll(listB);
// common now contains only the elements which are contained in listA and listB.