Set intersection

demo.java

import java.util.HashSet;
import java.util.Set;

class Untitled {
	public static void main(String[] args) {
		Set<String> s1 = new HashSet<String>();
		s1.add("a");
		s1.add("b");
		
		Set<String> s2 = new HashSet<String>();
		s2.add("b");
		s2.add("c");
		s2.add("d");

		s1.retainAll(s2);
		
		for (String k : s1) {
			System.out.println(k);
		}
	}
}