Polymorphism

We were introduced to polymorphism in Chapter 1, Object-oriented Design. It is a fancy name describing a simple concept: different behaviors happen depending on which subclass is being used, without having to explicitly know what the subclass actually is. As an example, imagine a program that plays audio files. A media player might need to load an AudioFile object and then play it. We'd put a play() method on the object, which is responsible for decompressing or extracting the audio and routing it to the sound card and speakers. The act of playing an AudioFile could feasibly be as simple as:

audio_file.play()

However, the process of decompressing and extracting an audio file is very different for different types of files. The .wav files are stored uncompressed, while .mp3, .wma, and .ogg files all have totally different compression algorithms.

We can use inheritance with polymorphism to simplify the design. Each type of file can be represented by a different subclass of AudioFile...