How to make a boolean variable switch between true and false every time a method is invoked?

Question

Hi,

I am trying to write a method that when invoked, changes a boolean variable to true, and when invoked again, changes the same variable to false, etc.

For example: call method -> boolean = true -> call method -> boolean = false -> call method -> boolean = true

So basically,

if (a = false) { a = true; }
if (a = true) { a = false; }

I am not sure how to accomplish this, because every time I call the method, the boolean value changes to true and then false again.

Thanks.

Answer 1

Just toggle each time it is called

public class A

  public A() {
    this.boolValue = false;
  }

  public void toggle() {
    this.boolValue = !this.boolValue;
  }
}

Answer 2

private boolean negate(boolean val) {
    return !val;
}

I think that is what you are asking for??

Answer 3

Without lookin at it, set it to not itself. I don't know how to write it in Java, but in Objective-C I would say

booleanVariable = !booleanVariable;

this flips the variable.

Answer 4

Assuming your code above is the actual code, you have two problems:

1) your if statements need to be '==', not '='. You want to do comparison, not assignment.

2) The second if should be an 'else if'. Otherwise when it's false, you will set it to true, then the second if will be evaluated, and you'll set it back to false, as you describe

if (a == false) {
  a = true;
} else if (a == true) {
  a = false;
}

Another thing that would make it even simpler is the '!' operator:

a = !a;

will switch the value of a.

Answer 5

value ^= true;

That is value xor-equals true, which will flip it every time, and without any branching or temporary variables.