4.1 The Incerment and Decrement Operators

Incrementing and decrementing are such common operations that Java provides special operators for them. The ++ operator adds one to the current value of an int or char. -- subtracts one. Neither operator works on doubles, booleans or Strings.

/**
 * This program demonstrates the ++ and -- operators.
 */
public class IncrementDecrement
{
   public static void main(String[] args)
   {
      int number = 50;

      // Display the value in number.
      System.out.println("Number is " + number);

      // Increment number.
      number++;

      // Display the value in number.
      System.out.println("Now, number is " + number);

      // Decrement number.
      number--;

      // Display the value in number.
      System.out.println("Now, number is " + number);
   }
}

Increment and decrement operators each have two forms: pre and post. In above example we have used the post form of increment and decrement operator

The example of the increment operator is:

Pre-increment:

  ++number;

Post-increment:

  number++

The example of the decrement operator is:

Pre-decrement:

  --number;

Post-decrement:

  number-- 

Both the pre- and post-increment operators increment the value of the variable by 1. Similarly, the pre- and post-decrement operators decrement the value of the variable by 1. The difference becomes apparent when the variable using these operators is employed in an expression.

Suppose a and b are int variables and:

  a = 5;
  b = 10 + (++a);

To execute the second statement, first the value of a is incremented to 6. Then, 10 is added to 6 to get 16, which is then assigned to b. Therefore, after the second statement executes, a is 6 and b is 16.

On the other hand, after the execution of:

  a = 5;
  b = 10 + (a++);

first the value of a is added to 10, which is then assigned to b, after execution of statement a is incremented. Therefore, after the second statement executes, a is 6 and b is 15.