Summary

In this chapter, we explored the concept of types and discussed how variables are specific types that can be explicitly or implicitly declared. We saw how in a statically-typed language (like Java), variables are not allowed to change types, though they can do so in a dynamically-typed language like Python. We also discussed how casting can convert a value stored in a variable into a different type. Implicit casts can happen automatically, but explicit casts must be indicated by the programmer using a cast operator, as the cast could result in loss of precision or the throwing of an exception.

We explored how class declarations and interface declarations create new types. We saw how polymorphic mechanisms like interface implementation and inheritance allow object to be treated as (and cast to) different types. We also introduced a few casting operators, which can be used to cast or test the ability to cast.

Finally, we explored how messages are dispatched when polymorphism is involved. We saw that the method invoked depends on what type the object was created as, not the type it is currently stored within.

Review Quiz

Check your understanding of the new content introduced in this chapter below - this quiz is not graded and you can retake it as many times as you want.