Booleans and Operator precedence

[leo donahue]

How does this happen?
boolean b1 = true;
boolean b2 = false;
boolean b3 = false;
b3 &= b1 | b2; // prints false...
b3 = b3 & b1 | b2; // prints true...
Operator precedence is &, ^, |
so why does the grouping change???
Is it because of the &= assignment operator? This is weird, but neat.

[leo donahue]

b2 should be true.

[Marilyn de Queiroz]

class Test
{
    public static void main( String[] args )
    {
        boolean b1 = true;
        boolean b2 = true;
        boolean b3 = false;
        
        System.out.println( b3 &= b1 | b2 ); // prints false...
        System.out.println( b3 &= b1 ); // prints false...
        System.out.println( b3 &= b2 ); // prints false...
        System.out.println( ( b3 & b1 ) | b2 ); // prints true...
        System.out.println( b3 & ( b1 | b2 ) ); // prints false...
    }
}  

The first println always prints false regardless of whether b1 and/or b2 are true or false because b3 is false. false & anything is false.
[ April 24, 2003: Message edited by: Marilyn de Queiroz ]

[Jim Yingst]

Is it because of the &= assignment operator?
Yes. &= has the same precendence as =, which is much lower than the precedence for & or |. So,
b3 &= b1 | b2
evaluates as
b3 &= (b1 | b2)
while
b3 = b3 & b1 | b2
evaluates as
b3 = ((b3 & b1) | b2)

[leo donahue]

Thank you sheriffs.
I appreciate your help.

[Stan James]

Things like this make good questions for tests, only because they have right and wrong answers and are easy to grade. I'd like to see choices in tests like:
A) This will print TRUE
B) This will print FALSE
C) Fire the programmer.
In practice, I never trust the compiler, my memory or my reader's memory, and always use parens to express my intent.