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We are now going to talk about the extract class refactoring. When a

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softer system evolves, we might end up with classes that really do the

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work of more than one class because we keep adding functionality to

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the class. Therefore also they're too

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big, too complicated. In particular, we might

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end up with a class that is doing the work of two

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classes. Typical examples are classes with many methods and quite a lot of

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data, quite a lot of fields. In this case, it's normally good idea

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to split the class into two, so what you will do, you will

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create a new class and move there the relevant fields and methods from

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the original class. So as to have two classes, each one implementing a

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piece of the functionality. Let's look at an example. In this case we're

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going to use a UML like representation for the class. We have this class Person

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that ends up representing also a phone number. And imagine that we add

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up these pieces, you know, a little bit at the time so we end

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up with something that really is doing the job of the person and

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of the phone number. So what we can do, we can actually do exactly

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what we described here. We split this class

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into a Person class, and the Phone Number class.

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And then we establish a use relation, so we

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have a reference of the phone number class into

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this class. And by separating the telephone number behavior

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into its own class, I once more improved the

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structure of the code, because now I have classes

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that are more cohesive, and do exactly one thing.