compilation error with ternary operator

Question

I tried the following with ternary operator and I do not understand why it is not compiling. The issue seems so small but I do not understand and hence bothers me -

Line 1 --> int a = false ? y+=1 : (x*=10);

Line 2 --> int b = false ? y+=1 : x*=10;

Line 1 compiles however Line 2 does not. Why ?

How is the parenthesis making a difference in case of 3rd operand and not the second operand. I didn't have to use parenthesis with anything else in the 2nd / 3rd operands (Unary, string, basic arithmetic ...) Why just assignment operator and that too specifically 3rd operand ?

Thanks in advance !

Answer 1

Without the () around x*=10, the entire left-hand operand of the *= operator is false ? y+=1 : x, as though you had:

int b = (false ? y+=1 : x)*=10;

And as false ? y+=1 : x isn't a variable, it can't be the left-hand operand of *=.

The assignment operators (including compound assignment, *= and such) are very, very low in the precedence list, below the conditional operator (? :):

Operators Precedence

• postfix: expr++ expr--
• unary: ++expr --expr +expr -expr ~ !
• multiplicative: * / %
• additive: + -
• shift: << >> >>>
• relational: < > <= >= instanceof
• equality: == !=
• bitwise: AND &
• bitwise: exclusive OR ^
• bitwise: inclusive OR |
• logical: AND &&
• logical: OR ||
• ternary: ? :
• assignment: = += -= *= /= %= &= ^= |= <<= >>= >>>=