Guava Set Unions

import com.google.common.collect.*;
import java.util.*;

class Example {
    public static void main(String[] args) {
        Set<String> a = Collections.newSetFromMap(new IdentityHashMap<>());
        Set<String> b = new HashSet<>();

        a.add("X");
        b.add(new String("X"));

        System.out.println(Sets.union(a, b)); // [X, X]
        System.out.println(Sets.union(b, a)); // [X]
    }
}