ob. serialization

[ashok khetan]

hi!
here is a ? on Object Serialization. Can we get question of this type in exam? 'coz interfaces like Externalizable and Serializable haven't been given in exam objectives.
thanx.
ashok.
_________
Question 80. (from <http://www.angelfire.com/or/abhilash/Main.html>; )
import java.io.*;
public class TransientWriter implements Externalizable {
private transient String s = "Hope I can ever be persistant!";

public void writeExternal(ObjectOutput oOut) throws IOException
{
oOut.writeObject(s);
}

public void readExternal(ObjectInput oIn) throws IOException, ClassNotFoundException
{
s=(String)oIn.readObject();
}
public String toString()
{
return s;
}
}
class K {
public static void main(String args[]) throws IOException, ClassNotFoundException {
TransientWriter tw = new TransientWriter();
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("tw.out"));
out.writeObject(tw);
ObjectInputStream in = new ObjectInputStream(new FileInputStream("tw.out"));
TransientWriter tw2 = (TransientWriter) in.readObject();
System.out.println(tw2);
}
}
Attempting to compile and run the above code

1) will cause a compiler error due to the attempt to write a transient object.
2) will cause a runtime exception when an attempt is made to write a transient object.
3) will not cause any runtime error and the transient object is writen to the file named "tw.out".
4) will not cause any runtime error and the transient object is not written to the file named "tw.out". The program prints a blank line on the screen.

[Gagan Indus]

hmmm... i really think tht we CAN get this type of q in exam , coz it seem to test our knowlegde about Object Streams , n transient keyword
( guess if serializable n externlizable are nt expicitly mentioned , still Object stream include them implicitly , no? LOL )
Just try to remember these things , Object streams can "serialize" n thus write-read only those objects which either implement :
-serializable interface ( Contanins no-method )
-or externlizable interface ( contanis only 2 methods wid sig :
public void writeExternal(ObjectOutput oOut) n public void readExternal(ObjectInput oIn)
And memebers wid modifier "transient" are not serialized even if the object implements serilizable
( the above code-ex serialize transient-memebers by explicitly implementing externalizable's method in such a way , externalizable is meant for this purpose , to overrule the default-functionality provided by seralizable )
this shld be enough i guess
------------------
Gagan (/^_^\)

[vipin bhatia]

Hi! I tried running the code but it gives following exception.

java.io.InvalidClassException: TransientWriter; IllegalAccessException
at java.io.ObjectInputStream.inputObject(ObjectInputStream.java:1224)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:386)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:236)
at K.main(K.java:32)
Exception in thread "main"
Tool completed with exit code 1
In tw.out the transient String is written, the contents of tw.out are ->
�� sr TransientWriter�`Z��X�� xpt Hope I can ever be persistant!x
Why am i getting the exception?

Originally posted by Gagan Indus:
hmmm... i really think tht we CAN get this type of q in exam , coz it seem to test our knowlegde about Object Streams , n transient keyword
( guess if serializable n externlizable are nt [b] expicitly mentioned , still Object stream include them implicitly , no? LOL )
Just try to remember these things , Object streams can "serialize" n thus write-read only those objects which either implement :
-serializable interface ( Contanins no-method )
-or externlizable interface ( contanis only 2 methods wid sig :
public void writeExternal(ObjectOutput oOut) n public void readExternal(ObjectInput oIn)
And memebers wid modifier "transient" are not serialized even if the object implements serilizable
( the above code-ex serialize transient-memebers by explicitly implementing externalizable's method in such a way , externalizable is meant for this purpose , to overrule the default-functionality provided by seralizable )
this shld be enough i guess
[/B]

[Gagan Indus]

Vipin ,
try this :
Type foll code in a filename called TransientWriter.java n compile it

import java.io.*; 
public  class TransientWriter implements Externalizable { 
private transient String s = "Hope I can ever be persistant!"; 
public void writeExternal(ObjectOutput oOut) throws IOException 
{ 
oOut.writeObject(s); 
} 
public void readExternal(ObjectInput oIn) throws IOException, ClassNotFoundException 
{ 
s=(String)oIn.readObject(); 
} 
public String toString() 
{ 
return s; 
} 
} 

Type foll code in a filename called K.java n compile n run it

import java.io.*;
public class K { 
public static void main(String args[]) throws IOException, ClassNotFoundException { 
TransientWriter tw = new TransientWriter(); 
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("tw.out")); 
out.writeObject(tw); 
ObjectInputStream in = new ObjectInputStream(new FileInputStream("tw.out")); 
TransientWriter tw2 = (TransientWriter) in.readObject(); 
System.out.println(tw2); 
} 
}

------------------
Gagan (/^_^\)