In this chapter, we covered the Flyweight pattern. 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. The Exaile music player for GTK+ uses Flyweight to avoid object duplication, and the Peppy text editor uses it to share the properties of the status bar.

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...