The Distributed and Non-distributed Models Contrasted

The Java platform's distributed object model is similar to the Java platform's object model in the following ways:

• A reference to a remote object can be passed as an argument or returned as a result in any method invocation (local or remote).
• A remote object can be cast to any of the set of remote interfaces supported by the implementation using the syntax for casting built into the Java programming language.
• The built-in instanceof operator can be used to test the remote interfaces supported by a remote object.
• The Java platform's distributed object model differs from the Java platform's object model in these ways:
• Clients of remote objects interact with remote interfaces, never with the implementation classes of those interfaces.
• Non-remote arguments to, and results from, a remote method invocation are passed by copy rather than by reference. This is because references to objects are only useful within a single virtual machine.
• A remote object is passed by reference, not by copying the actual remote implementation.
• The semantics of some of the methods defined by class java.lang.Object are specialized for remote objects. Since the failure modes of invoking remote objects are inherently more complicated than the failure modes of invoking local objects, clients must deal with additional exceptions that can occur during a remote method invocation.