The increment operator increases its operand by one. The decrement operator decreases its operand by one.
For example, this statement:
x = x + 1;
can be rewritten like this by use of the increment operator:
x++;
Similarly, this statement
x = x – 1;
x–;
These operators are unique in that they can appear both in postfix form, where they follow the operand as just shown, and prefix form, where they precede the operand. In the foregoing examples, there is no difference between the prefix and postfix forms. However, when the increment and/or decrement operators are part of a larger expression, then a subtle, yet powerful, difference between these two forms appears. In the prefix form, the operand is incremented or decremented before the value is obtained for use in the expression. In postfix form, the previous value is obtained for use in the expression, and then the operand is modified.
Example
x = 42;
y = ++x;
In this case, y is set to 43 as you would expect, because the increment occurs before x is assigned to y. Thus, the line y = ++x; is the equivalent of these two statements:
x = x + 1;
y = x;
However, when written like this
x = 42;
y = x++;
The value of x is obtained before the increment operator is executed, so the value of y is 42. Of course, in both cases x is set to 43. Here, the line y = x++; is the equivalent of these two statements
y = x;
x = x + 1;
class IncDec {
public static void main(String args[]) {
int a = 1;
int b = 2;
int c;
int d;
c = ++b;
d = a++;
c++;
System.out.println("a = " + a);
System.out.println("b = " + b);
System.out.println("c = " + c);
System.out.println("d = " + d);
}
}
The output of this program
a = 2
b = 3
c = 4
d = 1