The facade design pattern

The facade design pattern is a very simple pattern that provides a simplified interface to other code that may not be structured the same way. If we look facade up in the dictionary, this is one of the definitions we get:

An outward appearance that is maintained to conceal a less pleasant or creditable reality.

Google dictionary

This is the primary purpose of the pattern; to conceal a piece of code that isn't very nice to use and replace it with something better. That's all it is really, a class that calls code elsewhere.

Benefits

• Can change a badly-designed or hard to use API into an easy to use API
• Can merge multiple APIs into a single API
• If all calls to a function are done through a facade then it is very easy to refactor

Drawbacks

• Could possibly add unnecessary complexity if overused or used incorrectly

UML diagram

Code example

View on GitHub

public class FacadeClient {
    public static void main(String[] args) {
        Facade facade = new Facade();
        facade.doSomething();
    }
}

public class Facade {
    private Class1 class1;
    private Class2 class2;

    public Facade() {
        class1 = new Class1();
        class2 = new Class2();
    }

    public void doSomething() {
        class1.doSomething();
        class2.doSomething();
    }
}

public class Class1 {
    public void doSomething() {
        // ...
    }
}

public class Class2 {
    public void doSomething() {
        // ...
    }
}

Usage examples

• Creating a single consolidated API out of multiple, for example a FastSorter class (the facade) that exposes the functionality of the Quicksort, Merge sort and Heapsort classes I created in recent posts.
• Simplifying an overly-complex and difficult to use graphics API into a simplified version only containing the functions required for the application.