Applying the proxy pattern
In some applications, we want to execute one or more important actions before accessing an object. This is where the proxy pattern comes in. An example is accessing sensitive information. Before we allow any user to access sensitive information, we want to make sure that the user has sufficient privileges. The important action is not necessarily related to security issues. Lazy initialization (http://j.mp/wikilazy) is another case; we want to delay the creation of a computationally expensive object until the first time the user needs to use it. The idea of the proxy pattern is to help with performing such an action before accessing the actual object.
The proxy design pattern gets its name from the proxy (also known as surrogate) object, which is used to perform an important action before the actual object is accessed. There are four different well-known proxy types (http://j.mp/proxypat). They are as follows: