What is the difference between != and =! in Java? [duplicate]
I was looking over some mock OCJP questions. I came across a really baffling syntax. Here it is:
class OddStuff {
public static void main(String[] args) {
boolean b = false;
System.out.println((b != b));// False
System.out.println((b =! b));// True
}
}
Why does the output change between != and =!?
The question is just playing with you with confusing spacing.
b != b is the usual != (not equals) comparison.
On the other hand:
b =! b is better written as b = !b which is parsed as:
b = (!b)
Thus it's two operators.
- First invert
b. - Then assign it back to
b.
The assignment operator returns the assigned value. Therefore, (b =! b) evaluates to true - which is what you print out.
b != b means ! (b == b): the opposite of b == b.
b =! b is actually b = !b, an assignment. It's toggling b's value. An assignment evaluates to the value of the expression, so this will evaluate to !b (along with having changed the value of b).
b=!b is an assignment. It assigns b to !b and the expression evaluates to the resulting value, which is true.