Java Calendar YEAR returning zero when beeing initialized to static int

Question

I trying to understand the difference between the two lines below. Why is it returning a zero when I add static to the field.

private static final int this_year = Calendar.getInstance().get(Calendar.YEAR);

From this I get: this_year = 0;

private final int this_year = Calendar.getInstance().get(Calendar.YEAR);

And from this I get: this_year = 2013;

Someone who can explain why the first returns a zero?

Here's the code I use it in:

public class TheKing {
  public static final TheKing theKing = new TheKing();
  private final int beltSize;
  private static final int this_year = Calendar.getInstance().get(Calendar.YEAR);

  private TheKing() { 
    beltSize = this_year - 1930;
  }

  public int beltSize() {
    return beltSize;
  }

  public static void main(String[] args) {
    System.out.println("TheKing wears a size " + 
      theKing.beltSize() + " belt.");
  }
}

Both code blocks looks the same. Please organize your code in order to understand your problem. — Luiggi Mendoza, Feb 10 '13 at 19:27
`this_year = 2013` in both cases for me. How are you using the values elsewhere? — FThompson, Feb 10 '13 at 19:30
Other results than by @Vulcan. So far if used static, 2013 and all OK, non-static causes exception "referencing a non-static variable from static context" when I print it out. — petajamaja, Feb 10 '13 at 19:43

score 3 · Accepted Answer · answered Feb 10 '13 at 19:57

When fields are declared static, they are initialized in the static initialization method, meaning that your code looks like the following when compiled:

static {
    theKing = new TheKing();
    this_year = Calendar.getInstance().get(Calendar.YEAR);
}

Notice that the constructor is called before this_year is initialized, and before an int is initialized, it has its default value of 0. In other words, this_year is used before it is set to 2013.

One way to fix this is to simply reverse the order of the declarations:

private static final int this_year = Calendar.getInstance().get(Calendar.YEAR);
public static final TheKing theKing = new TheKing();

score 1 · Answer 2 · edited May 23 '17 at 12:18

Static methods are initialized in the order they are given in code.

public static final TheKing theKing = new TheKing();
private static final int this_year = Calendar.getInstance().get(Calendar.YEAR);

So the above would initialize theKing first, which calls the constructor, which uses the uninitialized value of 0 of this_year. If you were to change it to:

private static final int this_year = Calendar.getInstance().get(Calendar.YEAR);
public static final TheKing theKing = new TheKing();

it would work fine.

Or if you remove the static, this_year would get initialized as the object theKing is created.

Java Calendar YEAR returning zero when beeing initialized to static int

2 Answers2