What is the Composite Pattern and how to use it?

The Composite pattern is a design pattern that allows working with a group of cats (objects) in the same way as with a single cat (object). This pattern combines cats into a tree-like structure and allows clients to work uniformly with individual independent cats and groups of cats.

Let’s suppose we have a Cat class that represents a single cat. Now, let’s imagine that we want to create a hierarchy of cats to work with them as a single object. To do this, we can create an abstract class called CatComponent, which will have a common interface for working with both a single cat and a group of cats.

Now we can create two classes: SingleCat, which represents a single cat, and CatGroup, which represents a group of cats. The CatGroup class will have a list of CatComponent objects, which can be either individual cats or groups of cats.

Now we can create a hierarchy of cats:

In this example, we created three single cats: Fluffy, Mittens, and Whiskers. Then we created two cat groups: Group 1 and Group 2. We added Fluffy and Mittens to Group 1, and then added Group 1 and Whiskers to Group 2. Finally, we called the meow() method on Group 2, which made all the cats meow.

When we call the meow() method on Group 2, it first prints “Group 2”, and then calls the meow() method on each object in the catComponents list, including SingleCat Fluffy, SingleCat Mittens, and CatGroup Group 1. Each of these objects performs its own implementation of the meow() method, which prints its name and meows.

Thus, we used the composite pattern to work with a group of cats as if it were a single cat.

We created the abstract class CatComponent, which represents both single cats and groups of cats. Then we created the SingleCat and CatGroup classes, which implement the CatComponent interface and represent single cats and groups of cats, respectively. Each object in the cat hierarchy can perform its own meow(), and the meow() method for the cat group calls the meow() method for each object in the catComponents list, including other cat groups and single cats.

Meow :)

Here is what the UML diagram looks like:

P.S. Thanks to ChatGPT for the help with code generation :)

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