Serialization

[Swapnil Trivedi]

Q class Animal implements Serializable { Dog d; }

class Dog { }

When we attempt to serialize an instance of Animal class then what is the result:
a)One object is serialized
b)An exception is thrown at runtime.

Ans: one object is serialized..

My Doubt is what will be the bahaviour of Dog instance while serialization...
--->Since its not instantiated so the compiler will not throw any exception(or will it throw the "NotSerializable Exception"???)
--->Its not transient.If it would have marked transient then compiler would skip it...

So now in the given case when the Animal instance will be deserialized what would compiler will do with that instance???

Thanks!!!
Swapnil

[ankur rathi]

Originally posted by Swapnil Trivedi:
Q class Animal implements Serializable { Dog d; }

class Dog { }

When we attempt to serialize an instance of Animal class then what is the result:
a)One object is serialized
b)An exception is thrown at runtime.

Ans: one object is serialized..

My Doubt is what will be the bahaviour of Dog instance while serialization...
--->Since its not instantiated so the compiler will not throw any exception(or will it throw the "NotSerializable Exception"???)
--->Its not transient.If it would have marked transient then compiler would skip it...

So now in the given case when the Animal instance will be deserialized what would compiler will do with that instance???

Thanks!!!
Swapnil

I think, it should throw an exception...

[Keith Lynn]

No, you won't get an object serialized.

You will get a NotSerializableException

[Peter MacMillan]

No, you will not get an exception. As it is written, there is no Dog object for the serializer to write (dog is uninitialized in Animal). The serializer certainly knows how to write null and uninitialized values to an output, so there will be no error.

The serialization error will occur if you initialize dog - ie. give it a value - because the Serializer will not know how to serialized the Dog class (it does not implement Serializable).

This example should help you with the behaviour:

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
 

public class SerTest {
    public static class Bone {}   
    public static class Dog implements Serializable {
        private Bone bone; //1
        private String name;
        
        public Dog(String name) {
            this.name = name;
        }
        
        public String getName() {
            return name;
        }
    }
    
    public static void main(String[] args) {
        Dog dog = new Dog("Fido");
        ObjectOutputStream out;
        ObjectInputStream in;
        try {
            out = new ObjectOutputStream(new FileOutputStream("temp.dat"));
            out.writeObject(dog);
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
 
        try {
            in = new ObjectInputStream(new FileInputStream("temp.dat"));
            Object o = in.readObject();
            if (o instanceof Dog) {
                dog = (Dog)o;
                System.out.println("Got a dog, and his name is: " + dog.getName());
            } else {
                System.out.println("Poor pooch got lost  :(  .");
            }
            in.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Run that and you will get the output:

Got a dog, and his name is: Fido

Change the line maked by //1 to:

private Bone bone = new Bone();

Run it and you will get two serialization errors (one for the read and one for the write).

[Swapnil Trivedi]

Thanks Guys....Now I got it



Regards