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The Java distributed object model is similar to the Java 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 built-in Java syntax for casting.
- The built-in Java instanceof operator can be used to test the remote interfaces supported by a remote object.
The Java distributed object model differs from the Java object model in these ways:
- Clients of remote objects interact with remote interfaces, never with the implementation classes of those interfaces.
- Nonremote 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 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.