public class TestMethodsInCollection {
  public static void main(String[] args) {
    // Create set1
    java.util.Set<String> set1 = new java.util.HashSet<>();

    // Add strings to set1
    set1.add("London");
    set1.add("Paris");
    set1.add("New York");
    set1.add("San Francisco");
    set1.add("Beijing");

    System.out.println("set1 is " + set1);
    System.out.println(set1.size() + " elements in set1");

    // Delete a string from set1
    set1.remove("London"); // Remove "London" from set1
    System.out.println("\nset1 is " + set1);
    System.out.println(set1.size() + " elements in set1");

    // Create set2
    java.util.Set<String> set2 = new java.util.HashSet<>();

    // Add strings to set2
    set2.add("London");
    set2.add("Shanghai");
    set2.add("Paris");
    System.out.println("\nset2 is " + set2);
    System.out.println(set2.size() + " elements in set2");

    System.out.println("\nIs Taipei in set2? "
      + set2.contains("Taipei"));

    set1.addAll(set2); // Add all elements in set2 to set1
    System.out.println("\nAfter adding set2 to set1, set1 is "
      + set1);

    set1.removeAll(set2); // Remove all elements in set2 from set1
    System.out.println("After removing set2 from set1, set1 is "
      + set1);

    set1.retainAll(set2); // Retain all elements in set2 in set1
    System.out.println("After retaining common elements in set1 "
      + "and set2, set1 is " + set1);
  }
}