In this chapter, we covered three other structural design patterns: flyweight, MVC, and proxy.
We can use flyweight when we want to improve the memory usage and possibly the performance of our application. This is quite important in all systems with limited resources (think of embedded systems), and systems that focus on performance, such as graphics software and electronic games.
In general, we use flyweight when an application needs to create a large number of computationally expensive objects that share many properties. The important point is to separate the immutable (shared) properties from the mutable. We implemented a tree renderer that supports three different tree families. By providing the mutable age and x, y properties explicitly to the render() method, we managed to create only three different objects instead of eighteen. Although that might not seem like a big win, imagine if the trees were 2,000 instead of 18.
MVC is a very important design pattern used to structure an...