Devaka's Practice Exam1

[Balaji Bang]

Hi

Anyone please explain why it get compile time error at line 4
import java.io.*;

class A122{}
class B122 extends A122{}
class C122 extends A122 implements Serializable{}
final class D122 extends B122{}

public class PolyEx2{
     public static void main(String args[]){
          A122 a=new A122();
          B122 b=new B122();
          C122 c=new C122();
          D122 d=new D122();
          Object ob=c ;//Line-1
          System.out.println(ob);
          d=(D122)ob; //Line-2
          d=(D122)new B122(); //Line-3
        c=new Serializable(); //Line-4

[Punit Singh]

First of all it is wrong syntax to create anonymous class.

This is the right one:

 c=new Serializable(){};   

And as you might know, anonymous class can either extend only one class OR implement only one interface. It cannot extend a class and implement an interface together.

Compiler knows this thing and says I know this, I am not gonna allow you, I know anonymous class is implementing Serializable interface, so this anonymous class will never be able to extend class C122, it cannot be a subclass of class C122, so I will not allow this.

[James Tharakan]

Punit Singh wrote: I know anonymous class is implementing Serializable interface, so this anonymous class will never be able to extend class C122, it cannot be a subclass of class C122, so I will not allow this.

I did not understand what you are trying to say here. Can you try to tell that again

[Punit Singh]

Is this anonymous class possible James:

new Animal() impelements Barkable{};

or

new Serializable() extends C112{};

I am trying to say this.

[James Tharakan]

Okay... Now i understand that. :idea:

[Stephen Davies]

Correct me if I'm wrong, but isn't Serializeable an Interface? For this reason, how may one call new on the interface itself?

[Punit Singh]

Stephen Davies wrote:Correct me if I'm wrong, but isn't Serializeable an Interface? For this reason, how may one call new on the interface itself?

to make anonymous implementor class of Serializable.

[Stephen Davies]

Ahh, I see :roll: