Increment and Decrement Operators

Incrementing or decrementing by one is a common task in programs. This task can be accomplished by the statements:

n = n + 1; or n += 1;

Java also provides a unary operator called an increment operator, ++.

The statement n = n + 1 can be rewritten as ++n. The following statements are equivalent:

n = n + 1; ++n;

sum = sum + 1; ++sum;

Java also provides for a decrement operator, --, which decrements a value by one. The following are equivalent statements:

n = n - 1; --n;

sum = sum - 1; --sum;

The increment and decrement operators can be written as either a prefix or postfix unary operator. If the ++ is placed before the variable it is called a pre-increment operator (++number), but it can follow after the variable (number++), which is called a post-increment operator. The following three statements have the same effect:

++number; number++; number = number + 1;

Before looking at the difference between prefix and postfix unary operators, it is important to remember Java operators solve problems and often return values. Just as the assignment operator (=) returns a value, the ++ and -- operators return values. Consider the following code fragments:

The statement b = ++a uses the pre-increment operator. It increments the value of a and returns the new value of a.

The statement b = a++ uses the post-increment operator. It returns the value of a and then increments a by 1.

The precedence and associativity of the unary increment and decrement operators is the same as the unary - operator.