CSC Interview Question: how to find common elements between two collections
Solution: retainAll method do this. public boolean retainAll (Collection<?> c) Example: public class Test { public static void main(String [] args){ LinkedHashSet hs = new LinkedHashSet(); // add elements to the hash set hs.add("B"); hs.add("A"); hs.add("D"); hs.add("E"); hs.add("C"); hs.add("F"); System.out.println(hs); LinkedHashSet hs2 = new LinkedHashSet(); hs2.add("E"); hs2.add("C"); hs2.add("G"); System.out.println(hs2); boolean retain=hs.retainAll(hs2); System.out.println("retain:"+retain); System.out.println(hs2); System.out.println(hs); } } ********************************************** Output: [B, A, D, E, C, F] [E, C, G] retain:true [E, C, G] [E, C]