Serialization

[Hama Kamal]

hi guys...
please check my comment below line 20
shouldn't we get NullPointerException, since theCollar has not been initialized yet???

import java.io.*;
class Collar  {
private int collarSize;
public Collar(int size) { collarSize = size; }
public int getCollarSize() { return collarSize; }
}

class Dog implements Serializable {
transient private Collar theCollar; // we can't serialize this
private int dogSize;
public Dog(Collar collar, int size) {
theCollar = collar;
dogSize = size;
}
public Collar getCollar() { return theCollar; }
private void writeObject(ObjectOutputStream os) {
// throws IOException { // 1
try {
os.defaultWriteObject(); // 2
os.writeInt(theCollar.getCollarSize());      //  shouldn't we get NullPointerException, since theCollar has not been initialized yet???
} catch (Exception e) { e.printStackTrace(); }
}
private void readObject(ObjectInputStream is) {
// throws IOException, ClassNotFoundException { // 4
try {
is.defaultReadObject(); // 5
theCollar = new Collar(is.readInt()); // 6
} catch (Exception e) { e.printStackTrace(); }
}
}



public class SerializeDog {
public static void main(String[] args) {
Collar c = new Collar(3);
Dog d = new Dog(c, 5);
System.out.println("before: collar size is "
+ d.getCollar().getCollarSize());
try {
FileOutputStream fs = new FileOutputStream("testSer.ser");
ObjectOutputStream os = new ObjectOutputStream(fs);
os.writeObject(d);
os.close();
} catch (Exception e) { e.printStackTrace(); }
try {
FileInputStream fis = new FileInputStream("testSer.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
d = (Dog) ois.readObject();
ois.close();
} catch (Exception e) { e.printStackTrace(); }
System.out.println("after: collar size is "
+ d.getCollar().getCollarSize());
}
}

[John Stark]

The serialisation of the Dog object starts here:

os.writeObject(d);

The Collar object contained in this object was created and passed to the Dog constructor:

Collar c = new Collar(3);   
Dog d = new Dog(c, 5);

getCollarSize() is invoked on that Collar object:

os.writeInt(theCollar.getCollarSize()); 

So the Collar object was created on line 37 and everything should be fine, I think.

John

[Hama Kamal]

well John, and on which object the private methods get called ? on the Dog object ?

[Tommy Delson]

Serialization is not on the Exam, but it's good to learn and know about it.

Check out my responses on earlier post here to gain better understanding about Serialization.

https://coderanch.com/t/539469/java-programmer-SCJP/certification/Serialization

Hope it help...

[Hama Kamal]

Thansk Tommy, but are you sure that it is not on the exam?

[Tommy Delson]

Confirmed by Bert Bates, and you can confirm it by yourself by visit Oracle website under OCPJP's objectives. There is no Serialization objective on the exam.

[Hama Kamal]

Many thanks Tommy