After going through this,you refer to another link which consist of example for Serialization actualy where it is used mostly.From the below shown link just refer to topic "Example: Sensitive Information"
First up, it's important to note that classes don't get serialized - objects (class instances) get serialized.
1. What happens when we serialize a class at the JVM level.
From a high-level point of view, the object's state is transformed into a representation that can be used outside of the JVM, e.g. in a different JVM. There are different kinds of serialization supported by the JVM. The one that uses ObjectOutputStream produces a binary representation that can only be deserialized by a JVM. Another one use sthe java.beans.XMLEncoder class, and produces an XML representation if the class conforms to the JavaBenas specification.
2. Why do we need to serialize a class to send it across network.
Serialization is the process that turns an object that exists inside of a JVM into something that can be used outside of it. As such, it's a necessary step for sending an object someplace else.
3. What happens if we dont serialize a class.
I'm not sure what you're asking. If you don't serialize an object, then you don't have a serialized representation of it. But that's probaly not what you're asking?