In recent years there has been a lot of hype concerning a concept called patterns. Patterns are really just another attempt to document and reuse abstractions. The idea of a pattern is to create a description of a set of proven and useful relationships between objects. These descriptions can then be a guide used to help in the solution of new problems.

The idea is perhaps best illustrated with a simple example. Lets consider the proxy pattern. The proxy is useful when we have a client and server relationship, but there are details concerning the way in which the client and server are connected that are unimportant as far as the client is concerned. Most often this is found in networks, where the client is found on one machine, and the server is found on another. The details of trasferring information across the network are unimportant to the client, who simply wants some information. One way to address this problem is to create a proxy. The proxy has the same interface as the server, but does not perform the given operations. Instead, the proxy handles the marshalling of information across the network, the reception of the results, and hands back the results to the client. In this fashion the client is isolated from needing to know the network details.

We will examine many more patterns in a later chapter.

[audio] [real] Text to accompany slide20, in Chapter 2 of An Introduction to Object-Oriented Programming