import java.util.*

 public class SetExample {
   public static void main(String[] args) {
	 Set set = new HashSet();
	 set.add("one");
	 set.add("second");
	 set.add("3rd");
	 set.add(new Integer(4));
	 set.add(new Float(5.0F));
	 set.add("second"); // duplicate, not added
	 set.add(new Integer(4)); // duplicate, not added
	 System.out.println(set);
   }
 }

結果：
[one, second, 5.0, 3rd, 4]