What are rules of serialization in Java?

Here is a summary of some rules of Java serialization:

• An object is serializable only if its class or its superclass implements the Serializable (or  Externalizable) interface.
• An object is serializable (itself implements the Serializable interface) even if its superclass is not. However, the first superclass in the hierarchy of the serializable class, that does not implements Serializable interface, MUST have a no-arg constructor. If this is violated, readObject() will produce a java.io.InvalidClassException in runtime.
• The no-arg contructor of every non-serializable superclass will run when an object is deserialized. However, the deserialized objects? constructor does not run when it is deserialized.
• The class must be visible at the point of serialization.
• All primitive types are serializable.
• Transient fields (with transient modifier) are NOT serialized, (i.e., not saved or restored). A class that implements Serializable must mark transient fields of classes that do not support serialization (e.g., a file stream).
• Static fields (with static modifier) are Not serialized.
• If member vairiables of a serializable object reference to a non-serializable object, the code will compile but a RumtimeException will be thrown.

Discover the secrets of the Java Serialization API is a nice article about this topic.