Warning Common mistake is to use the == operator to test class types for equality.

Note: Using == for class types will not generate a compile error, but it is WRONG! Using == just compares the addresses, not the values of class objects.

Example: basic types

Use == to test for equality for basic types.

    1   public static void main(String[] args)
    2   {
    3     Scanner in = new Scanner(System.in);
    4     int x, y;
    5   
    6     x = in.nextInt();
    7     y = in.nextInt();
    8   
    9     if (x == y) {
   10       System.out.printf("equal");
   11     } else {
   12       System.out.printf("not equal");
   13     }
   14   }

Example: class types

Use the equals method to test for equality for class types.

    1   public static void main(String[] args)
    2   {
    3     Scanner in = new Scanner(System.in);
    4     String x, y;
    5   
    6     x = in.next();
    7     y = in.next();
    8   
    9     if (x.equals(y)) {
   10       System.out.printf("equal");
   11     } else {
   12       System.out.printf("not equal");
   13     }
   14   }