Java Network Programming, Second Edition

The java.rmi.server Package

The java.rmi.server package is the most complex of all the RMI packages; it contains the scaffolding for building remote objects and thus is used by objects whose methods will be invoked by clients. The package defines 6 exceptions, 9 interfaces, and 10 classes. Fortunately, you need to be familiar with only a few of these to write remote objects. The important classes are the RemoteObject class, which is the basis for all remote objects; the RemoteServer class, which extends RemoteObject; and the UnicastRemoteObject class, which extends Remote Server. Any remote objects you write will likely either extend or use UnicastRemoteObject. Clients that call remote methods but are not themselves remote objects don’t use these classes, and therefore don’t need to import java.rmi.server.

The RemoteObject Class

Technically, a remote object is not an instance of the RemoteObject class but an instance of any class that implements a Remote interface. In practice, most remote objects will be instances of a subclass of java.rmi.server.RemoteObject:

public abstract class RemoteObject extends Object 
 implements Remote, Serializable

You can think of this class as a special version of java.lang.Object for remote objects. It provides toString( ), hashCode( ), clone( ), and equals( ) methods that make sense for remote objects. If you create a remote object that does not extend RemoteObject, you need to override these methods yourself.

The equals( ) method compares the remote ...