javapost-incrementoperator-precedenceocpjp

a = (a++) * (a++) gives strange results in Java

I'm studying for the OCPJP exam, and so I have to understand every little strange detail of Java. This includes the order in which the pre- and post-increment operators apply to variables. The following code is giving me strange results:

int a = 3;

a = (a++) * (a++);

System.out.println(a); // 12

Shouldn't the answer be 11? Or maybe 13? But not 12!

FOLLOW UP:

What is the result of the following code?

int a = 3;

a += (a++) * (a++);

System.out.println(a);
Solution

  • After the first a++ a becomes 4. So you have 3 * 4 = 12.

    (a becomes 5 after the 2nd a++, but that is discarded, because the assignment a = overrides it)