Java - static initialization

Question

I have written a piece of code :

public class Child{
int y ;
private static final int z = getZ();

static {
    System.out.println("The value of z is "+z);
}

public int getX(){
    System.out.println("get x");
    return 10;
}

public int getY(){
    Child ch = new Child();
    System.out.println("get y");
    ch.y = getX();
    return y;
}

public static int getZ(){
    System.out.println("get z");
    return new Child().getY();
}

public Child(){
    System.out.println("Child constructor");
}


public static void main(String...args){
    Child ch = new Child();
    System.out.println("the value of z in main is "+z);
}
}

And the output is :

get z
Child constructor
Child constructor
get y
get x
The value of z is 0
Child constructor
the value of z in main is 0

Can anyone please explain me why the value of z is 0 and not 10 ?

EDIT:- Thanks everyone , I got the answer to my first question . I still have a doubt , as far as I know the static blocks are executed after the class is loaded and before the first object of the class is instantiated . Well then the SOP("The value of z is "+z) should have been executed before SOP("Child constructor") ! Ain't it ?

Answer 1

Look at getY():

public int getY(){
    Child ch = new Child();
    System.out.println("get y");
    ch.y = getX();
    return y;
}

The first three lines are irrelevant - they don't change the value of y in this instance, which is what gets returned.

You're creating an awful lot of pointless objects in frankly spaghetti code, called while initializing the same class that you're constructing instances of. I suggest you try to keep your code a lot simpler than this. Static initializers should be avoided where possible to start with, let alone ones that go all round the houses to do no useful work.

Answer 2

because getY() sets ch.y to 10, but returns the value of this.y.

Answer 3

In GetY you return this.y which never gets set.

Answer 4

On getY() you returned the uninitialized y variable instead of the Child ch instance.

Answer 5

Its because inside getY() method you are constructing a new CHild object and you are assigning 10 to that instance of variable y and when you return y that will be the current instance variable y. I hope it explains .

Answer 6

To your second point, static fields and static blocks are initialized / executed in textual order.

Eg:

public class StaticTest()
{
  static
  {
    System.out.println("s1 in block 1 :" + s1);
  }

  private static String s1 = "s1";

  static
  {
    System.out.println("s1 in block 2 : " + s1);
  }

  public static void main(String args[])
  {
    new StaticTest();
  }
}

The output of this will be -

s1 in block 1 :

s1 in block 2 : s1