Nice Serialization Question

[Leandro Coutinho]

Nice Serialization Question

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

class Animal {
	Animal(String name)
	{
		System.out.println("Animal constructor. My name is " + name);
	}
}

class Dog extends Animal implements Serializable {

	Dog() { super("Duck"); }

	public static void main(String[] args)
			throws IOException, ClassNotFoundException {
		Dog dog = new Dog();
	
		FileOutputStream fos = new FileOutputStream("dog.ser");
		ObjectOutputStream os = new ObjectOutputStream(fos);
		os.writeObject(dog);
		
		FileInputStream fis = new FileInputStream("dog.ser");
		ObjectInputStream is = new ObjectInputStream(fis);
		dog = (Dog)is.readObject();
	}
}

What do you think is the output?

[Trivikram Kamat]

Leandro Coutinho wrote:
What do you think is the output?

The code compiles fine, but gives InvalidClassException on running.
It runs without exception if the code which reads the serialized file is commented.

[Rahul Saple]

It would compile fine but would return a InvalidClassException when run.

When Dog(serializable sublass) is deserialised it would call the default constructor of its superclass because the superclass(Animal) isn't a Serializable Object.
Since the Animal class doesnt have a default constructor it would raise a flag and throw a suitable exception.

If you modify your code to look like this

   
class Animal {
    Animal()
    {
          System.put.printn("Inside Animal's default constructor");
    }
    Animal(String name)  
    {  
        System.out.println("Animal constructor. My name is " + name);  
    }  
}   
}    

then the code would not throw the exception when deserializing.

[Wouter Oet]

Remember that although it is nice to know about, serialization is no longer on the current exam.

[Leandro Coutinho]

Wouter Oet wrote:Remember that although it is nice to know about, serialization is no longer on the current exam.

Thanks for pointing out. I didn't know that. I just looked the Exam Topics and it's not there


Annotations are not on the exam too. And these two are important topics.

[Wouter Oet]

Accept for @Override, @SupressWarnings and @Deprecated, annotations aren't used often in Java SE. They're used very often in Java EE but the Java EE exams cover those topics in detail.