Test

import java.util.Set;
import java.util.HashSet;
class Test{
	public static void main(String[] args){
		
		Set<String> a = new HashSet<String>();
		Set<String> b = new HashSet<String>();
		
		a.add("a");
		b.add("b");

		Set<String> c = union(a, b);
		System.out.println(c.size());

	}

	public static <E> Set<E> union(Set<E> s1, Set<E> s2) {
       		Set<E> result = new HashSet<E>(s1);
       		result.addAll(s2);	
       		return result;
	}
}