Serialization

The process of writing objects and their exact states into a linear format using I/O streams. The output format is not human readable. The output can be written to a file, a network, or a database. Serialized object data is stored in a .ser file.

State of an object can also be stored in a custom text format, which is not recommended.

A class must implement Serializable interface (from java.io package) to be serialized. Otherwise, NotSerializableException is exception is thrown. The ObjectOutputStream class serializes objects, and feeds the output to another output stream.

Deserialization

The process of constructing the object from serialized format on the heap. ObjectInputStream, which reads from a input stream, is used to deserialize.

Serializable fields

When a class is made serializable, all of its fields must be serializable.

• All primary types are serializable
• Built-in objects such as String, URL, Date, Point, Random are serializable
• All collections from java.util package

Transient fields

Fields can be defined as transient. Will not be serialized. Reverts to null or default value primitive type when deserialized.