Things you can do with Sets : Abstract Set « Collections « Java Tutorial

1. Java Tutorial
2. Collections
3. Abstract Set

import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.TreeSet;

public class MainClass {
  static void fill(Set s) {
    s.addAll(Arrays.asList("one two three four five six seven".split(" ")));
  }

  public static void test(Set s) {
    System.out.println(s.getClass().getName().replaceAll("\\w+\\.", ""));
    fill(s);
    fill(s);
    fill(s);
    System.out.println(s); // No duplicates!

    s.addAll(s);
    s.add("one");
    s.add("one");
    s.add("one");
    System.out.println(s);

    System.out.println("s.contains(\"one\"): " + s.contains("one"));
  }

  public static void main(String[] args) {
    test(new HashSet());
    test(new TreeSet());
    test(new LinkedHashSet());
  }
}

HashSet
[one, two, five, four, three, seven, six]
[one, two, five, four, three, seven, six]
s.contains("one"): true
TreeSet
[five, four, one, seven, six, three, two]
[five, four, one, seven, six, three, two]
s.contains("one"): true
LinkedHashSet
[one, two, three, four, five, six, seven]
[one, two, three, four, five, six, seven]
s.contains("one"): true