How Can I Find Common Elements Between Two Lists in Java?

Finding Common Elements in Lists

To identify the shared elements between two lists, you can employ Collection#retainAll(). By utilizing this method, you can conveniently retain only the elements present in both lists, effectively eliminating any unique elements from either list.

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

Alternatively, if you wish to preserve the original listA, you can create a new list to hold the common elements:

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

For enthusiasts of streams, a clever approach involves filtering based on containment using Stream#filter() and Collection#contains():

List<Integer> common = listA.stream().filter(listB::contains).toList();
// common now contains only the elements contained in both listA and listB.

While this may appear more concise, it is also at least twice slower in execution.

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