Java Examples in a Nutshell, 3rd Edition

A Multiuser Domain

A multiuser domain, or MUD, is a program (a server) that allows multiple people (clients) to interact with each other and with a shared virtual environment. The environment is typically a series of rooms or places linked to each other by various exits. Each room or place has a textual description that serves as the backdrop and sets the tone for the interactions between users. Many early MUDs were set in dungeons, with place descriptions reflecting the dark, underground nature of that imaginary environment. In fact, the MUD acronym originally stood for “multiuser dungeon.” Some MUDs serve primarily as chat rooms for their clients, while others have more of the flavor of old-style adventure games, where the focus is on exploring the environment and problem solving. Others are exercises in creativity and group dynamics, allowing users to add new places and items to the MUD.

Examples Example 21-4 through Example 21-8 show classes and interfaces that define a simple user-extensible MUD system. A program like this MUD example clearly demonstrates how the RMI programming paradigm transcends the client/server model. As we’ll see, MudServer and MudPlace are server objects that create the MUD environment within which users interact. But at the same time, each user within the MUD is represented by a MudPerson remote object that acts as a server when interacting with other users. Rather than having a single server and a set of clients, then, this system is really a distributed ...