Order of Static initialization Block,Instance initialization Block and Constructor....

[Shanu Pandey]

If in a code we have a instance initialization code then that code is executed after the constructor's call to the super() is complete.

class Grandparent {
    // Static init block
    static {
        System.out.println("static - grandparent");
    }

    // Instance init block
    {
        System.out.println("instance - grandparent");
    }

    // Constructor
    public Grandparent() {
        System.out.println("constructor - grandparent");
    }
}

class Parent extends Grandparent {
    // Static init block
    static {
        System.out.println("static - parent");
    }
   
   // Instance init block
    {
        System.out.println("instance - parent");
    }

    // Constructor
    public Parent() {
        System.out.println("constructor - parent");
    }


}
class Child extends Parent {
    // Static init block
    static {
        System.out.println("static - child");
    }

    // Instance init block
    {
        System.out.println("instance - child");
    }
	
	// Constructor
    public Child() {
        System.out.println("constructor - child");
    }
}

public class LoadTest {
    public static void main(String[] args) {
        System.out.println("START");
        new Child();
        System.out.println("END");
    }
}

The output should be:
START
static - grandparent
static - parent
static - child
constructor - grandparent
instance - grandparent
constructor - parent
instance - parent
constructor - child
instance - child
END

But the actual Output is:

START
static - grandparent
static - parent
static - child
instance - grandparent
constructor - grandparent
instance - parent
constructor - parent
instance - child
constructor - child
END

please make it clear why??

[Matt Cartwright]

The instance initializer needs to
be executed before the constructor returns control.

public class StaticTest
{

   private int a = 12;
   
   static
   {
      System.out.println("StaticTest - static");
   }

   {
      System.out.println("StaticTest - BEGIN - instance");
      System.out.println("a = " + a);
      System.out.println("StaticTest - END - instance");
   }


   StaticTest()
   {
      System.out.println("StaticTest - constructor");
      System.out.println("a = " + a);
   }

   public static void main( String[] args )
   {
      System.out.println("START");
      new StaticTest();
      System.out.println("END");
   }
}

This is how 'a' gets initialized

And the output is:

StaticTest - static
START
StaticTest - BEGIN - instance
a = 12
StaticTest - END - instance
StaticTest - constructor
a = 12
END


HTH
Matt