import java.util.HashSet; public class test22_HS { public static void main(String[] args) { // TODO Auto-generated method stub HashSet<Object>hs=new HashSet<>(); hs.add("a"); hs.add(5); hs.add("a"); hs.add(null); System.out.println(hs); } } op::[null, a, 5] | 0 |