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Latest Thinking In Java Articles - Page 6

Arrays

Most of the necessary introduction to arrays is in the last section of Chapter 4, which shows how you define and initialize an array. Holding objects is the focus of this chapter, and an array is just one way to hold objects. But there are a number of other ways to hold objects, so what makes an array special?

Summary

Both inheritance and composition allow you to create a new type from existing types. Typically, however, you use composition to reuse existing types as part of the underlying implementation of the new type and inheritance when you want to reuse the interface. Since the derived class has the base-class interface, it can be upcast to the base, which is critical for polymorphism, as you’ll see in the next chapter.

Summary

Polymorphism means “different forms.” In object-oriented programming, you have the same face (the common interface in the base class) and different forms using that face: the different versions of the dynamically-bound methods.

Upcasting

In Chapter 6 you saw how an object can be used as its own type or as an object of its base type. Taking an object handle and treating it as the handle of the base type is called upcasting because of the way inheritance trees are drawn with the base class at the top.

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