need of Serializable interface in java? As there are no methods in the interface. and how does it maintain state of an object?

Question

Hi classes which implement serializable interface what exactly they implement as there are no methods in the interface.And how does it help in maintaining state of object across a network.

Answer 1

No interface maintains state, of course. It's a marker interface, like Remotable.

Answer 2

It doesn't maintain state itself. But it marks the class as requiring serialisation, and the runtime then knows to serialise that class, and its components (excluding fields marked as transient).

It's useful to explicitly mark classes as being serialisable and fields as transient (i.e. not to be serialised). Otherwise you could inadvertently serialise everything in your program for transmission over the network. That likely is not what you want. You wouldn't want to serialise entities like factories. Nor credentials like passwords. Not to mention the payload size :-)

Answer 3

It is a marker interface. Additional discussion can be found here: http://stackoverflow.com/questions/1995198

In short, the interface is used via reflection-based code that inspects the type information at run time, and if if the object in question implements that interfacre then certain actions are taken (in the case of Serializable: object is saved/loaded to/from a stream).

Answer 4

From Wikipedia:

.... serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file, a memory buffer, or transmitted across a network connection link .....

You can do things with serialized objects that you cannot do with non serialized objects. Instead of using using a webservice to pass data from client to server, you can put all of the info into a serialized bean and avoid any xml parsing and binding.

You can take a serialized bean and write it out to a file, save it in a database as a blob.

The serialized interface provides the ability for you to implement a level of persistence and durability.

Answer 5

serializable is a marker interface. serializable interface makes java recognize the implementing class object can be serialized(means write the byte information of object into files or any other channels). So, it means if you want to make a class object can be serialized you have to make that class flagged with serializable interface. Otherwise, throws IOException like it wont serialze the object.

Why this Exception would be thrown? because, developer should decide about serializing an object and deserializing the same later would have any use or not. When there is no use of serializing developer wont want his object to be serialized by him or any other developer using his class. Take for example, Socket class; It wont implement serializable interface because If you can serialize socket and close application and launches the application again and deserialize the same socket object. In the mean while connected server through socket is down. Is there any use of serializing the socket class object?