Static members not initialized as expected

Question

The following code simply subtracts a value (10 in this case, just for the demonstration) from the current year obtained by using the java.util.Calendar class.

public final class Test
{   
    private static final Test TEST = new Test();
    private static final int YEAR = Calendar.getInstance().get(Calendar.YEAR);
    private final int eval=YEAR - 10;

    public static void main(String[] args)
    {
        System.out.println("Evaluation "+TEST.eval);
    }
}

I expect this code to display 2003 (current year - 10) but instead, it displays -10. I assume the constant YEAR hasn't been initialized. Why does this happen in this case?

Answer 1

This happens because you are initializing Test before you have initialized YEAR - meaning it will go to the (implicit) constructor and initialize eval to YEAR-10 before YEAR has a value (so it defaults to 0).

As denoted in the comments, simply changing the order of YEAR and TEST in the initialization will do the trick.

Answer 2

Because it's not static - you have to create an object in order to use this field! (or change it to static)

Try:

public final class Test
{   
    private static final Test TEST = new Test();
    private static final int YEAR = Calendar.getInstance().get(Calendar.YEAR);    
    private final int eval=YEAR - 10;

    public static void main(String[] args)
    {
        Test t = new Test();
        System.out.println("Evaluation "+t.eval);
    }
}

Answer 3

Make eval static and it will work. If you do not want it static, then do the computation in the main method.

Answer 4

As others have mentioned, the problem is in the order of the static fields. But, you can avoid the ordering problem entirely by lazily initializing TEST using a method (like is done in the singleton pattern):

public final class Test
{   
    private static Test TEST = null;
    private static final Test getInstance() {
        if (TEST == null) {
            TEST = new Test();
        }
        return TEST;
    }

    private static final int YEAR = Calendar.getInstance().get(Calendar.YEAR);
    private final int eval=YEAR - 10;

    public static void main(String[] args)
    {
        System.out.println("Evaluation "+Test.getInstance().eval);
    }
}