Explain RMI.

RMI is Java infrastructure and APIs that allow distributed method calls. In a little more detail: a client program on machine X calls method calcShippingCosts() on a remote object on machine Y. What RMI does is that there is a proxy object on the client that includes the calcShippingCosts() method. The client calls this method on the proxy object. The proxy then converts the method call into a TCP/IP message to the remote JVM. The TCP message is read by the remote JVM and forwards the call to the remote object. The remote object performs the calculation and returns the result to the remote JVM. The remote JVM converts the result into a return message to the client-side proxy object. The proxy object converts the TCP response message into a Java value which is then returned to the client object as the result of its calcShippingCosts() method call.

A good reading about RMI is here