I had a question in my test that I got confused about (code attached below). To put it shortly, I thought that the variables are reassigned and then added back as a value to the expression (making the output "8, 10") but seems like the original value somehow is not changed. What am I missing?
p.s. Sorry if a similar question exists, I couldn't find one (probably its too obvious :P).
class InitTest{
public static void main(String[] args){
int a = 10;
int b = 20;
a += (a = 4);
b = b + (b = 5);
System.out.println(a + ", " + b);
}
}
a += (a = 4);
The above is logically equivalent to the following:
a = a + (a = 4);
If we substitute in the existing value for a, then this simplifies to:
a = 10 + 4 = 14
We can do the same for b:
b = b + (b = 5) = 20 + 5 = 25
We see this result because of operator precedence. The addition operator, +, has a higher precedence than the assignment operator, =, as defined by the Java operator precedence table.
You can see that the addition-assignment operator, +=, shares the same precedence with the assignment operator, in which case the expression is evaluated from left to right.
If, instead, the expressions were:
a = (a = 4) + a;
b = (b = 5) + b;
Then it would result in the output that you expect (a = 8, b = 10), as the left operand is computed before the right operand (when evaluating the expression). I'll try to locate where this is specified in the Java Language Specification.