Serialization is the process of writing the state of an object to a byte stream. This is useful when you want to save the state of the object (content of the object) to a persistent storage area, such a file. For example if you want to maintain record of the temprature on a particular place at every hour then you can serialize your object and save the temprature at every hour in a file. Only an object that implements the java.io.Serializable interface can be saved.
Serialization is writing the state of the object to a byte stream. This is useful when you want to save the state of the object in a persistent storage such as file.