Final variable return zero before initialize

[Siva Masilamani]

Hi

I have doubt about the following program

  final int j = SomeMethod();   // forward referencing method SomeMethod()

    int SomeMethod() {
        System.out.println("j is "+j);//line 2
        return j; 
    }  

I know java does not initialize the final variable instead it expect us to provide the value.

But in the above case why it is returning j value as zero.

How come in line 2 j value becomes zero?

[John de Michele]

Siva:

Actually, all member variables are defaulted to null for references, false for booleans, and 0 for other primitives, regardless of being final. Since your method doesn't actually change the value of j (it just assigns the value of itself to itself), your answer is 0.

John.

[Seetharaman Venkatasamy]

final variable gets the value before the constructor finish the execution .so you assign the method inside the constructor

final int j;

  
Constructor()
{
   j = aMethod();
} 

int aMethod()
{
  return 42;
}
 

Hope this helps

[Siva Masilamani]

John de Michele wrote:Siva:

Actually, all member variables are defaulted to null for references, false for booleans, and 0 for other primitives, regardless of being final. Since your method doesn't actually change the value of j (it just assigns the value of itself to itself), your answer is 0.

John.

But i have read somewhere that java does not assign default value to final variable because if it assigs default value then it can not be changed,so it expect us to provide the value.

Could you please explain this?

[John de Michele]

Siva:

Well, your program ran, so whoever wrote that was incorrect. If Java didn't assign a default, you'd probably get a random number. I did a test to check all three cases:

public final class SandBox {

    public static void main(String[] args) {
        SomeClass someClass = new SomeClass();
        someClass.someMethod();
        someClass.someOtherMethod();
        someClass.aThirdMethod();
    }

}

final class SomeClass {
    final int j = someMethod();
    final String k = someOtherMethod();
    final boolean t = aThirdMethod();

    public int someMethod() {
        System.out.println("j is '" + j + "'");
        return j;
    }

    public String someOtherMethod() {
        System.out.println("k is '" + k + "'");
        return k;
    }

    public boolean aThirdMethod() {
        System.out.println("t = '" + t + "'");
        return t;
    }

}

I consistently get this result:

j is '0'
k is 'null'
t = 'false'
j is '0'
k is 'null'
t = 'false'

So clearly, final variables get assigned defaults.

John.

[Siva Masilamani]

Thanks John for your valuable information.

I appreciate it.

[John de Michele]

Siva:

Glad I could help.

John.