1.2 System Goals

The goals for supporting distributed objects in the Java language are:

• Support seamless remote invocation on objects in different virtual machines.
• Support callbacks from servers to applets.
• Integrate the distributed object model into the Java language in a natural way while retaining most of the Java language's object semantics.
• Make differences between the distributed object model and local Java object model apparent.
• Make writing reliable distributed applications as simple as possible.
• Preserve the safety provided by the Java runtime environment.

Underlying all these goals is a general requirement that the RMI model be both simple (easy to use) and natural (fits well in the language).

In addition, the RMI system should allow extensions such as garbage collection of remote objects, server replication, and the activation of persistent objects to service an invocation. These extensions should be transparent to the client and add minimal implementation requirements on the part of the servers that use them. To support these extensions, the system should also support:

• Several invocation mechanisms; for example simple invocation to a single object or invocation to an object replicated at multiple locations. The system should also be extensible to other invocation paradigms.
• Various reference semantics for remote objects; for example live (nonpersistent) references, persistent references, and lazy activation.
• The safe Java environment provided by security managers and class loaders.
• Distributed garbage collection of active objects.
• Capability of supporting multiple transports.

The first two chapters in this specification describe the distributed object model for the Java language and the system architecture. The remaining chapters describe the RMI client and server visible APIs which are part of JDK 1.1.