Creation date: 21 March, 2011

Postfix operators

We know that postfix operators(++ and --) are applied after evaluation of expression.

int n = 5;
System.out.println(++n);

will print 6, when

System.out.println(n++);

will print 5 because autoincrement applied after completion of println operation. Now look at the following tricky example and try to predict the result.

class A {
  static int n=5;
  public static void main(String[] args) {
     n=n++;
     System.out.println(n);
  }
}

The common sense (I mean logic) says, that first n = n will set n to 5, then autoincrement will be applied (because of postfix rules) and the value of n will be 6. The result must be the value 6. Now scroll down and look the real output of execution.

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The Java's logic decides that the result must be 5. Now let's try to understand this logic. I think so. First of all the assigning value is prepared, but not yet set to n. Then incrementation is applied to n (the right side of = operator), and finally the prepared before value is set to n. Hence incremented value is overriden by previous value. It's the only thing I can imagine.

Author: Jafar N.Aliyev (Jsoft)

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