instance initializer

[Geethakrishna Srihari]

Why is B printed twice between X and Y:

public class Test
{
int i=fun();
int j=5;
int fun(){
System.out.println("A");
return 1;}
public static void main(String[] args)
{
System.out.println("X");
Test t=new T();
System.out.println("Y");
System.out.println(t.i);
System.out.println(t.j);



}

}
class T extends Test
{
int i=fun();
int j=10;
int fun()
{
System.out.println("B");
return 2;
}
}

[Chitra AP]

It is because you have overridden the fun() method in the subclass.

---------------
Test t=new T();
------------------

So, when you instantiate the subclass, it instantiate the parent class first. At that time it runs fun() (overridden in sub class which prints B)
and when the sub class instantiates again it prints B.

Hope it clears your doubt.

[Geethakrishna Srihari]

Only constructors makes a call to parent constructors - Do overridden methods also follow suit?

[Geethakrishna Srihari]

But why B is printed twice? Even if thats the case A followed by B shud be, and not B twice? Please clarify

[Henry Wong]

Originally posted by Geethakrishna Srihari:
Only constructors makes a call to parent constructors - Do overridden methods also follow suit?

An overriden method does not, by default, call the method that it is overriding. However, you can call the super class' method, by using the super keyword. (e.g. super.fun())

Henry

[Henry Wong]

Originally posted by Geethakrishna Srihari:
But why B is printed twice? Even if thats the case A followed by B shud be, and not B twice? Please clarify

The reason B is being printed twice, is because the fun() method is being called twice. Notice that there are two i variables, that you are initializing.

Henry

[Shweta R Dhaneshwar]

Hi,
I am getting really confused here.int fun() is overriden in T(subclass)....so ,if one wants to call the fun() method from subclass T it would be resovled depending upon the type of actual object...this is run time polymorphism...right!!!...but when you want to refer the method fun() from superclass Test why does it call the sub class fun()?

[Nischal Tanna]

  
 
public class Test
{
int i=fun();

{
System.out.println("Inside Test");
System.out.println(i);
}

static
{
System.out.println("Inside static of parent");
}
int j=5;
int fun()
{
System.out.println("A");
return 1;
}

public static void main(String[] args)
{
System.out.println("X");
Test t  = new Child();
System.out.println("Y");
}
}
 
class Child extends Test
{
int i=fun();

static
{
System.out.println("Inside static of Child");
}

{
System.out.println("Inside Child");
System.out.println(i);
}

int j=10;

int fun()
{
System.out.println("B");
return 2;
}
} 

The above code reflects that before initialising child class instance variables it goes to initialise parent.
This occurs coz before creating the child instance , parent class is loaded as well as its instance is created !!..

[Lalitha Gottumukkula]

Shweta,

Although we are initializing t in the Test's class, it is the T instance we are assigning to the Test reference variable(t). So, we are instantiating the subclass.

Try with this example for more clarification.

public class X {
int i=fun();
int j=5;
int fun() {
System.out.println("A");
return 2;
}
public static void main(String[] args) {
X t = new X(); // prints A
X t1 = new Y(); // prints B B
X t2 = new Z(); // prints C C C
}
}
class Y extends X {
int i1=fun();
int j1=10;
int fun() {
System.out.println("B");
return 2;
}
} 
class Z extends Y {
int i2=fun();
int j2=15;
int fun() {
System.out.println("C");
return 3;
}
}

Hope this will clear your doubt.

Thanks,
Lalitha.

[Amol Fuke]

I did not get the explanation of above code .
Can you please explain in detail?

[soumya ravindranath]

Remembered reading this some time back

http://www.javaranch.com/maha/Discussions/Language_Fundamentals/Constructor_-_JavaRanch_Big_Moose_Saloon.htm

[Nischal Tanna]

Originally posted by Amol Fuke:
I did not get the explanation of above code .
Can you please explain in detail?

Read my code... the lady who has posted after my reply has messed up the explaination

[amit taneja]

Originally posted by Nischal Tanna:

The above code reflects that before initialising child class instance variables it goes to initialise parent.
This occurs coz before creating the child instance , parent class is loaded as well as its instance is created !!..

the code by nischal tanna ..produces the following results

D:\java_prac>java Test
Inside static of parent
X
Inside static of Child
B
Inside Test
2
B
Inside Child
2
Y



can anybody pls explain the step by step..how it printed
i got most of the logic but stuck
that how 2 is printed after Inside Test

??

[Piyush Sam]

2 is printed after inside Test bcoz parent class is initialize first before the child class and
{
System.out.println("Inside Test");
System.out.println(i);
}
this block of code gets executed before this code

{
System.out.println("Inside Child");
System.out.println(i);
}

and then program prints
B // int i=fun(); of child class
Inside Child // first line of fun() of child class
2 // second line of fun() of child class

[Timmy Marks]

There is an excellent chapter on initialization in Bruce Eckel's Thinking in Java available free online. Should explain all you need to know about object initialization.