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 achiev

Answer 1

You can get the common elements between two lists using the method "retainAll". This method will remove all unmatched elements from the list to which it applies.

Ex.: list.retainAll(list1);

In this case from the list, all the elements which are not in list1 will be removed and only those will be remaining which are common between list and list1.

List list = new ArrayList<>();
list.add(10);
list.add(13);
list.add(12);
list.add(11);

List list1 = new ArrayList<>();
list1.add(10);
list1.add(113);
list1.add(112);
list1.add(111);
//before retainAll
System.out.println(list);
System.out.println(list1);
//applying retainAll on list
list.retainAll(list1);
//After retainAll
System.out.println("list::"+list);
System.out.println("list1::"+list1);

Output:

[10, 13, 12, 11]
[10, 113, 112, 111]
list::[10]
list1::[10, 113, 112, 111]

NOTE: After retainAll applied on the list, the list contains common element between list and list1.