Point to ponder on Static initializer

[Vaibhav Wahee]

Take a look at the code below it's form K&B but slightly altered
class Main{
static{ System.out.print("Test ");}
{System.out.print("b1 ");}
public Main()
{ System.out.print("b2 ");}

}
class Main2 extends Main
{
static { System.out.print("r1 ");}
public Main2()
{ System.out.print("r2 ");}
{ System.out.print("r3 ");}
static {System.out.print("r4 ");}
}

class Main3 extends Main2
{
static { System.out.print(" In Main2 ");}
public static void main(String [] args)
{
System.out.print("Pre ");
new Main3();
System.out.println("Hawk ");
}
}

GIVES OUTPUT AS FOLLOWS
Test r1 r4 In Main2 Pre b1 b2 r3 r2 Hawk

The K&B Book fails to mention an important point....the static initializers are called as per the call hierarchy....the one which is called the first is the one from the base class Main and then followed by Main2 and Main3 respectively...a point never mentioned in K&B

[Vaibhav Wahee]

Can you now predict the output ???

package javaapplication5;
 
class Main{
    static{ System.out.print("Test ");}
 
    {System.out.print("b1 ");}
 
    public Main() { System.out.print("b2 ");}
 
    public static void main(String [] args) {
        System.out.print("Pre ");
        new Main3();
        System.out.println("Hawk ");
    }
}
 
class Main3 extends Main2 {
    static { System.out.print(" In Main2  ");}
   
}
 
class Main2 extends Main {
    static { System.out.print("r1 ");}
 
    public Main2() { System.out.print("r2 ");}
    { System.out.print("r3 ");}
    static {System.out.print("r4 ");}
}

(Edit: formatted to be humanly readable)
[ May 15, 2007: Message edited by: Barry Gaunt ]

[Keith Lynn]

What page is the example on?

[Harish Paravasthu]

Hi,

Here is the output..

Test Pre r1 r4 In Main2 b1 b2 r3 r2 Hawk

Harish
[ May 15, 2007: Message edited by: Harish Paravasthu ]

[Vaibhav Wahee]

it's on page 265

[Keith Lynn]

Look at the comments under Initialization Blocks on page 257.

The point of the example is that before a class is initialized, all superclasses must be initialized. That causes the static initializers and static blocks to be executed.

[Vaibhav Wahee]

In the answer of the second example above why is r3 coming before r2 even though the instance initializer r2 comes before r3 ???

[Keith Lynn]

Printing out r3 happens in an instance initializer block, and printing out r2 happens in the constructor of the class.

When a constructor begins to execute, it first makes a call to a superclass constructor. After the superclass has finished initializing, the instance variable initializers and instance initializer blocks are executed in order, then the remainder of the constructor is executed.

[Barry Gaunt]

instance initializer r2

?

It looks like it's in a constructor to me.

[Vaibhav Wahee]

Yeah alright thanks..but still the K&B book fails to mention the point in its exactness ......What do you think ??

[Barry Gaunt]

Sorry Keith, I missed your reply while I was formatting that mess up there.

[Nik Arora]

Its Understood