serialisation

[vishvar hariraman]

Hi everybody

Serialisation s the process of writing a state of an object into a persistent medium. Why we need serialisation. I cant get thro with the above single statement.

pls clarify to me friens
Thx

[Jon Egan]

Some definitions and typical uses of Serialization might clear it up:

definitions:

1. state of an object - the values of the instance variables of the object... including the instance variables of any object-type instance variable of this object, and the instance variables held by ... see recursion.

2. persistent medium - disk file, database, etc.... something not "in memory".


Where an object is an "in-memory" concept, Serialization is the "not in memory" way to store an object, so it can be brought back into memory later, or by a different process.

examples:

1. Your app needs to shut down, and start up again later, with the same "state" (variables having the same value as before). You can write out the object-type variables to disk or a database by serializing them.

2. Your app needs to "talk to" another app across a network, and share data that are represented in-memory as objects that both apps understand. With serialization, you can send the objects across a socket connection with the other app. (Note that this example isn't about a "persistent medium",it's a different use of serialization)

Serialization is conceptually like this:

public class XyzPdq implements Serializable {
    private int x;
    public void setX(int inX) { x = inX; }
    public int getX() { return x; }
 
    private String y;
    public void setY(String inY) { y = inY; }
    public String getY() { return y; }
}
 
// now in some code somewhere else (please disregard the syntax,
// method arguments, etc., just trying to convey a concept)....
 
XyzPdq xp = new XyzPdq();
xp.setX(5);
xp.setY("Hello World");
 
// ObjectOutputStream is used to write objects to a stream writing to
// something, where the "something" is a socket, or an open file, ...
ObjectOutputStream oos = new ObjectOutputStream([I]something[/I]);
oos.write(xp);
 
// now think of the file as containing [I][B]something like[/B][/I]:
5HelloWorld
 
// later ....
ObjectInputStream is = new ObjectInputStream(something);
// where the "something" is that same file, now opened for reading...
 
XyzPdq xp2 = (XyzPdq)iss.read();
xp2.getX(); // gives 5
xp2.getY(); // gives "Hello World"
 

At this point, you don't have the exact same object (that is, xp and xp2 are at different memory addresses, possibly in different processes, possibly on a different server)... but you have an equivalent object, one with the exact same state.


Hope this helps,
-- Jon

[vishvar hariraman]

Excellent Response!!!
No words...

THX A LOT JON.