Java前缀运算符的行为

Question

I was wondering why following code returns 0. I thought num2 will be incremented before applied to *= and the second line would execute num2 = 1*1

int num2 = 0;
num2 *= ++num2;
System.out.println(num2);

Answer 1

From JLS :

A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T) ((E1) op (E2)) , where T is the type of E1 , except that E1 is evaluated only once.

So, your code is equivalent to:

num2 = (int) (num2 * ++num2);

The left-hand operand of the multiplication is zero, thus the result is zero.