Earlier this semester in my Software Design class, we had an assignment where we were to choose to write a report on either the Proxy, Facade, or Decorator design patterns (or any combination of the three, for extra credit). I had chosen the Decorator pattern, and due to the amount of assignments I had due I never went back to examine Proxy or Facade. So I’m here to do just that with the assistance of Sourcemaking’s article on it, starting with Proxy.
The Proxy is a structural design pattern that adds a wrapper to an object so that the object itself doesn’t suffer from excess complexity. There are actually a large number of reasons where this is useful. Sometimes objects get excessively resource heavy, and you don’t want to instantiate them unless absolutely necessary. Sometimes you’d just like an extra layer of protection from the access of an object for the sake of security or for general ease of use. Consider getter and setter methods for an example — you don’t want open access to the data within your object, so you make the data private (hidden from outside access) and you instead create public methods for retrieving and change the data of the private variables. In a way, getter and setter methods are mini proxies. Of course, the difference is that proxies are meant to be entire objects in themselves.
For a real-world example I’ll reference Sourcemaking’s article. In order to make a payment, someone would use the funds that they have in their bank account. Instead of needing to add methods such as “makePayment()” to their account and increasing the Account’s complexity, it is possible instead to pay with a check which can indirectly access the funds of the account. In this example, the check is the proxy to the Account class. Here’s a UML-like diagram:
The Proxy design pattern serves many purposes and is perhaps one of the easiest design patterns (in my opinion, of course) to understand and use. It’s very similar to Decorator in structure (which I did a project on earlier this semester) but its’ implementation is slightly different. Decorators are used to add new functionality to an object, whereas the Proxy is designed to encapsulate existing functionality into another, “adjacent” object.
James Blash 