Defines the Remote Method Invocation (RMI) API.

The Remote Method Invocation (RMI) API is a Java API that allows a Java program to invoke methods on objects running on remote JVMs (Java Virtual Machines), similar to how Java programs can invoke methods on local objects. RMI enables distributed computing in Java by providing a way for a Java object in one JVM to invoke methods on a remote Java object in another JVM.

Key components and concepts of the RMI API include:

1. Remote Interface: An interface in Java that extends java.rmi.Remote. This interface defines the methods that can be invoked remotely.
2. Remote Object: An object that implements a remote interface and extends java.rmi.server.UnicastRemoteObject. Remote objects are instantiated on the server side and can be accessed by remote clients.
3. RMI Registry: A simple lookup service that binds names to remote objects. Clients can look up remote objects in the registry by specifying a name.
4. Stubs and Skeletons: In earlier versions of RMI, stubs and skeletons were used to facilitate communication between the client and the server. Stub objects on the client side act as proxies for remote objects, intercepting method calls and forwarding them to the actual remote objects. Skeleton objects on the server side receive method invocations from stubs and delegate them to the appropriate remote objects. However, in modern Java versions (Java 5 and later), stubs and skeletons are generated automatically by the RMI system and are transparent to the developer.
5. RMI Invocation: Clients invoke methods on remote objects as if they were invoking local methods. The RMI system handles the details of marshalling method parameters into a format suitable for transmission over the network, sending the method invocation to the remote JVM, executing the method on the remote object, and marshalling the return value (if any) back to the client.
6. Security: RMI supports various security measures to protect against unauthorized access and ensure data integrity during remote method invocations. This includes using Java's security manager, digital certificates, and codebase annotations to specify the locations from which classes are loaded.

To use the RMI API, developers typically perform the following steps:

• Define the remote interface that specifies the methods to be invoked remotely.
• Implement the remote interface with a concrete class that extends UnicastRemoteObject.
• Create and start an RMI registry on the server side using LocateRegistry.createRegistry(port) or by launching rmiregistry from the command line.
• Bind the remote object to a name in the RMI registry using Naming.rebind("name", remoteObject).
• On the client side, look up the remote object from the RMI registry using Naming.lookup("name").
• Use the remote object as if it were a local object, invoking methods defined by the remote interface.

Overall, the RMI API simplifies the development of distributed applications in Java by abstracting away much of the complexity involved in remote method invocations, allowing developers to focus on the business logic of their applications.