Anonymous class..

[Preethi Dev]

Hi , i got it from Devaka's lab

is it true that Anonymous class cannot be used to cast?

class A{}
class B exetnds A implements java.io.Serializable{}
class casting
{
public static void main(String args[])
{

A a=new A();
B b=new B();
b=(B)new Serializable(){};//compiler error and says that inconvertible types

}
}


Thanks
Preetha

[James Tharakan]

As far as understood ,anonymous class EXTENDS a class.
b=(B)new Serializable(){};

So here you are trying to extend a interface(Serializable).

Somebody correct me if i am wrong.

[Bindu Lakhanpal]

new Serializable(){} is implementing the inteface Serializable to create an anonymous class object.
In case of explicit casting,at compile time, when both the source type and target type are classes,one class must be a subclass of the other and new Serializable(){} is not a subclass or superclass of B.
[ December 27, 2008: Message edited by: Daisy Lakhanpal ]

[Treimin Clark]

Originally posted by James Tharakan:
As far as understood ,anonymous class EXTENDS a class.
b=(B)new Serializable(){};

So here you are trying to extend a interface(Serializable).

Somebody correct me if i am wrong.

Sorry James, you are wrong. Anonymous inner classes can be used to both 'extends' and 'implements' tasks.

The problem is with the "reference type" of an anonymous inner class. Look at that anonymous inner class declaration fragment:
new Serializable(){}

How do you think about the above inner class expression? Do you think it is same as to, something like:
Serializable innerClass = new Anonymouse();

No! But actually it is same as to:
Anonymous innerClass = new Anonymouse();

(where Anonymous is something that implements the Serializable interface)


Now consider the following program:

import java.io.*;
 
class A{}
 
class B extends A implements java.io.Serializable{}
 
class casting{

public static void main(String args[]){

A a=new A();
B b=new B();

class C implements Serializable{
}

[B]b=(B)new Serializable(){};[/B]//compiler error and says that inconvertible types
[B]b=(B)new C();[/B] //compiler error and says that inconvertible types
 
}
}

Both of the above two statements gives you a compile time error, because of the SAME reason. Try to understand through the above program.

[James Tharakan]

thanks for the correction...
Now i realize how stupid i was when i posted it.
Now things are clear
[ December 25, 2008: Message edited by: James Tharakan ]