Advance Java

• RMI lets Java objects on different hosts communicate with each other in a way that’s similar to how objects running in the same virtual machine communicate with each other: by calling methods in objects. • A remote object lives on a server. Each remote object implements a remote interface that specifies which of its methods can be invoked by clients. Clients invoke the methods of the remote object almost exactly as they invoke local methods. For example, an object running on a local client can pass a database query as a String argument to a method in a database object running on a remote server to ask it to sum up a series of records. The server can return the result to the client as a double. This is more efficient than downloading all the records and summing them up locally. • From the programmer’s perspective, remote objects and methods work pretty much like the local objects and methods we’re accustomed to. All the implementation details are hidden. • More formally, a remote object is an object with methods that may be invoked from a different Java virtual machine than the one in which the object itself lives, generally one running on a different computer. Each remote object implements one or more remote interfaces that declare which methods of the remote object can be invoked by the foreign system. RMI is the facility by which a Java program running on one machine, say java.oreilly.com, can invoke a method in an object on a completely different machine.