Understanding the output of an arithmatic expression

Question

I have a java class as follows:

class A{
    public static void main(String[] args){
       int a=10;
       a*=a++ +a;
       System.out.println(a);
    }
}

Ou         


        

Answer 1

Consider 15.7.1. Evaluate Left-Hand Operand section of java specs where it says - First, the left-hand operand is evaluated to produce a variable then the value of the right-hand operand are used to perform the binary operation indicated by the compound assignment operator

In your case it is a = 10 * ((11)+10) = 201

Answer 2

In any statement of the type:

x *= y;

The initial value of the LHS is evaluated before the RHS. So your statement:

a *= a++ + a;

Is equivalent to:

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

Which sets a to the value 10 * (10 + 11) => 210.

If you're particularly interested in the formal specification related to this point you can find it here which contains the rule "If the operator is a compound-assignment operator (§15.26.2), then evaluation of the left-hand operand includes both remembering the variable that the left-hand operand denotes and fetching and saving that variable's value for use in the implied binary operation."