Nextstep Object-Oriented Programming and the Objective C by Next Computer Inc

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Polymorphism also permits code to be isolated in the methods of different objects rather than be gathered in a single function that enumerates all the possible cases. This makes the code you write more extensible and reusable. When a new case comes along, you don’t have to reimplement existing code, but only add a new class with a new method, leaving the code that’s already written alone. For example, suppose you have code that sends a draw message to an object. Depending on the receiver, the message might produce one of two possible images.

For example, a Faucet needs to keep track of how much water is being used over time. To do that, you could either implement the necessary methods in the Faucet class, or you could devise a generic Meter object to do the job, as suggested earlier. Each Faucet would have an outlet connecting it to a Meter, and the Meter would not interact with any object but the Faucet. The choice often depends on your design goals. If the Meter object could be used in more than one situation, perhaps in another project entirely, it would increase the reusability of your code to factor the metering task into a separate class.

In addition, collaboration is often impeded by barriers of time, space, and organization. ■ Code must be maintained, improved, and used long after it’s written. Programmers who collaborate on a project may not be working on it at the same time, so may not be in a position to talk things over and keep each other informed about details of the implementation. ■ Even if programmers work on the same project at the same time, they may not be located in the same place. This also inhibits how closely they can work together.

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