transient

What are transient variables? What role do they play in Serialization process?
The transient keyword in Java is used to indicate that a field should not be serialized. Once the process of de-serialization is carried out, the transient variables do not undergo a change and retain their default value. Marking unwanted fields as transient can help you boost the serialization performance.

Why static variables are not serialized?
The Java variables declared as static are not considered part of the state of an object since they are shared by all instances of that class. Saving static variables with each serialized object would have following problems:

It will make redundant copy of same variable in multiple objects which makes it in-efficient.
The static variable can be modified by any object and a serialized copy would be stale or not in sync with current value.