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

java post-increment operator-precedence ocpjp
Marius picture Marius · Nov 7, 2011 · Viewed 7.2k times · Source

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);

Answer

Bozho picture Bozho · Nov 7, 2011

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)

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