retainAll(Collection c) method

retainAll(Collection c): This retainAll in Java method returns only those elements from the ArrayList which are present in the specified collection.

boolean retainAll(Collection<?> c)

Where c is the collection that you want to retain from the ArrayList.
return type:  Its return type is boolean. It can return either true or false.
If specified collection c presents in ArrayList then it returns true after retaining otherwise it returns false.

import java.util.ArrayList;
public class ArraylistExample 
{
	public static void main(String[] args) 
        {
		ArrayList<Integer> listOfNames = new ArrayList<Integer>();
		listOfNames.add(1);
		listOfNames.add(2);
		listOfNames.add(3);
		listOfNames.add(4);
		listOfNames.add(5);
		listOfNames.add(6);
				
		ArrayList<Integer> listOfNames2 = new ArrayList<Integer>();
		listOfNames2.add(4);
		listOfNames2.add(5);
		listOfNames2.add(6);
				
		listOfNames.retainAll(listOfNames2);
	  
	         for(Integer number : listOfNames)
	           	System.out.println("Name from list = "+ number);
	}
}

Output: Name from list = 4
Name from list = 5
Name from list = 6