Externalizable Class , Can any one help ?

[Hassan Ebied]

Can any one please see the below code snippet and tell me what could the correct result

I was preparing for SCJP exam and I got stuck with such a question

[i]import java.io.*;

public class Ques05 
{
              public static void main(String[] args) throws Exception
                   {
                             ObjectOutputStream output = new ObjectOutputStream(
                                 new FileOutputStream("shapes"));
                                   output.writeObject(new Square(5));
                                   output.writeObject(new Circle(5));
                                   output.close();
                                   ObjectInputStream input = new ObjectInputStream(
                                   new FileInputStream("shapes"));
                                  ((Square)input.readObject()).draw();
                                  ((Circle)input.readObject()).draw();
                     }
}
abstract class 
     DrawingObject implements Serializable
   {
          public abstract void draw();
   }
class Square extends DrawingObject
    {
          private int a;
          public Square(int a)
          {
               this.a = a;
          }
          public void draw()
         {
              System.out.println("Drawing a square with measurement:" + a);
         }
  }
class Circle extends 
        DrawingObject implements Externalizable
        {
            private int radius;
            private double circumference;
            public Circle(int radius){
                this.radius = radius;
            }
            public void draw(){
            System.out.println("Drawing a circle with radius:" + radius + "
                                       and circumference:" + circumference);
            }
          @Override
           public void readExternal(ObjectInput in) 
               throws IOException
           {
                radius = in.readInt();
                circumference = 2 * Math.PI * radius;
           }
          @Override
           public void writeExternal(ObjectOutput out) 
                  throws IOException {
                         out.writeInt(radius);
                   };
}

[/i]
List of choices are

1. The program will compile and run normally to produce the desired output.
2. The program will not compile as it is not possible for the Circle class to implement
both the Serializable and Externalizable interfaces.
3. The program will complain at run-time telling that there is no default constructor for
the class 'Square'.
4. The program will complain at run-time telling that there is no default constructor for
the class 'Circle'.

[Henry Wong]

"Hassan Ebied",

Please Quote Your Sources.

Thanks,
Henry

[Hassan Ebied]

Thanks Hinry for your comment
and sorry for posting question without qouting the sources which violate the rules

I have got the above questions from Mock exams bought from javabeat.com , objective 3

http://www.javabeat.net/javabeat/scjp5/mocks/scjp-5-0-objective3.php

[sudipto shekhar]

I think not quoting your sources does not violate the rule as far as i think..but it is provided for the poster and so that the reader could read it in a very clear manner and can also refer to the code through line numbers. So just quoting the source makes everything easy and makes every one happy

[Mumtaz Khan]

When an Externalizable object is reconstructed, an instance is created using the public no-arg constructor, then the readExternal method is called.
Since the class circle doesn't contain a non-arg constructor and compiler doesn't provide non-arg constructor , it should complain at run time telling that there is no default constructor for class circle. So answer should be 4.

[Bert Bates]

Keep in mind sports fans that Externalizable is NOT on the SCJP exam.

hth,

Bert

[Hassan Ebied]

But Mumtaz ,,

Externizable is an interface not a class , so it has no constructors

When I compiled this code and run it , it gave me the desired output

Bert , Are you sure that this class will not be included in the exam. I dont know , If I will face such question in the exam I will tell them that Bert told me that it is not included in the exam and no body will care about me.

[Abhi vijay]

Hassan, if you have read K&B -6, you will realize that Externalizable is not for the exam.

[Bert Bates]

Hi Hassan,

Well, no one is perfect, as anyone who has been at the ranch for a while can tell you, I've made my share of mistakes... okay, lots more than my share . But I will say that I'm very careful when I make a statement like that.

hth,

Bert

[Hassan Ebied]

Bert ,

I am sorry I missed what i want to say


Many thany thanks for you words , I really appreiate all replies and I did not meant to heart any one . I just wanted to say it in funny way,,,,


Again sorry Bert and Thanks ofcourse

[Bert Bates]

No worries Hassan,

good luck with your studies,

Bert