Change boolean Values?

Question

I have a question about boolean values in Java. Let's say I have a program like this:

boolean test = false;
...
foo(test)
foo2(test)

foo(Boolean test){
  test = true;
}
foo2(Boolean test){
  if(test)
   //Doesn't go in here
}

I noticed that in foo2, the boolean test does not change and thereby doesn't go into the if statement. How would I go about changing it then? I looked into Boolean values but I couldn't find a function that would "set" test from true to false. If anyone could help me out that would be great.

Answer 1

You're passing the value of a primitive boolean to your function, there is no "reference". So you're only shadowing the value within your foo method. Instead, you might want to use one of the following -

A Holder

public static class BooleanHolder {
  public Boolean value;
}

private static void foo(BooleanHolder test) {
  test.value = true;
}

private static void foo2(BooleanHolder test) {
  if (test.value)
    System.out.println("In test");
  else
    System.out.println("in else");
}

public static void main(String[] args) {
  BooleanHolder test = new BooleanHolder();
  test.value = false;
  foo(test);
  foo2(test);
}

Which outputs "In test".

Or, by using a

member variable

private boolean value = false;

public void foo() {
  this.value = true;
}

public void foo2() {
  if (this.value)
    System.out.println("In test");
  else
    System.out.println("in else");
}

public static void main(String[] args) {
  BooleanQuestion b = new BooleanQuestion();
  b.foo();
  b.foo2();
}

Which, also outputs "In test".

Answer 2

You named your parameter the same as an instance variable. Here, the parameter is the one referenced, not the instance variable. This is called "shadowing", where the simple name test as a parameter name shadows the instance variable also called test.

In foo, you changed the parameter test to true, not the instance variable test, which was unchanged. That explains why it doesn't go into the if block in foo2.

To assign the value, get rid of the parameter on foo, or use this.test to reference the instance variable.

this.test = true;

and

if (this.test)