Instance Initializer means what

[Kaarthick Ramamoorthy]

abstract class Abs
{
private int i;
public abstract void first();
{ // What these three lines specifies and when it will be executed
System.out.println("in first");

}
}

Please help me. What ie meant by Instance Initializer here.

[Vaibhav Chauhan]

if you make a subclass of class Abs, and make an object of the subclass then initializer in class Abs gets called as

try this code:

  
   abstract class Abs
{
private int i;
public abstract void first();
{ 
System.out.println("in first");
}
}
 
class SubClass extends Abs{

public SubClass(){
System.out.println("in SubClass constructor");
}
{
System.out.println("in second");
}
public void first(){

}
}
 
public class TestAbstractInitializer{
public static void  main(String [] args){
SubClass s=new SubClass();
}
}

output is:
in first
in second
in SubClass constructor

i hope you are clear now.

[Srinivas Kalvala]

Hello,

It is the block which will be executed before the constructor when object of a class type is create. but if there is static{} block present in the class type then it will be executed first time for first object and will not be executed for second object.

[Srinivas Kalvala]

Hello,

Take following program for example:


class hai{
static{
System.out.println("Iam in static block");
}
{
System.out.println("Iam in init block");
}
}
class din{
public static void main(String s[])
{
System.out.println("Hello");
hai h=new hai();
hai hello=new hai();
}
}


output:

Hello
Iam in static block
Iam in init block
Iam in init block

[Kaarthick Ramamoorthy]

Thanks.

[Barry Gaunt]

It is important to realize that the instance initializer(s) are executed first no matter which constructor is executed. So you can use them for common initialization code.
[ September 04, 2006: Message edited by: Barry Gaunt ]

[Mohan Shankar]

If I understand correctly, in the above code they are creating the anonomous inner class. The code present inside the scope is the constuctor of the inner class without any name (ie., anonymous).
What is not clear to me is when this inner class is defined static, how all the instance of the outer class refer to the same instance of the inner class.
That is, conceptually, all the different objects are instantiating the same inner class.

[bing marquez]

Hi Mahantesh

No, those are not anonymous inner classes. They are static blocks and init blocks as explicitly stated. For the exam, one way of spotting anonymous inner class is that following the definition of "new Class()" is an opening curly brace, instead of the usual ";". Then at the end of the closing curly brace, you'll find the semicolon instead "};"

For example:

    
     AnonymousClass an = new AnonymousClass() {
// more code
     };

Or if the anomymous class is argument defined:

    
     someMethod(new AnonymousClass() {
// more code
     });

In which case the semicolon is after the closing parenthesis "});".
[ September 04, 2006: Message edited by: bing marquez ]