Why does if(Boolean.TRUE) {…} and if(true) {…} work differently in Java

Question

I want to know the difference between Boolean.TRUE and true values inside an if clause. Why does it give me a compilation error (that

Answer 1

The difference exists because one is a true constant while the other is just mimicking one.

The compiler will look at things like if statements and try to figure out whether they will always be a given expression (== true, == false, == null, etc) but it will only do this up to a certain level.

In the case of true there is no ambiguity: it will always undoubtedly represent "true". However Boolean.TRUE is just a field, which is apparently not as far as the compiler is willing to go.

public static final Boolean TRUE = new Boolean(true);

Think for example about what would be done if reflection is involved.

You can see this clearly when you introduce an extra level of complexity:

public static void main(String[] args) {
    int x;
    if(getCondition()) {
        x = 5;
    }
    System.out.println(x);
} 

private static boolean getCondition(){
    return true;
}

Even though the expression will always be true, the compiler still complains that x might be unassigned. Only the most rudimentary verification is done to help you.