Polymorphism

We were introduced to polymorphism in Chapter 1, Object-Oriented Design. It is a showy 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. It is also sometimes called the Liskov Substitution Principle, honoring Barbara Liskov's contributions to object-oriented programming. We should be able to substitute any subclass for its superclass.

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 can 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...