Java™ How To Program (Early Objects), Tenth Edition

Tagging Interfaces

We’ll see in Chapter 15, Files, Streams and Object Serialization, the notion of tagging interfaces (also called marker interfaces)—empty interfaces that have no methods or constant values. They’re used to add is-a relationships to classes. For example, in Chapter 15 we’ll discuss a mechanism called object serialization, which can convert objects to byte representations and can convert those byte representations back to objects. To enable this mechanism to work with your objects, you simply have to mark them as Serializable by adding implements Serializable to the end of your class declaration’s first line. Then, all the objects of your class have the is-a relationship with Serializable.