Chapter 14. Protecting Members: Do Not Disturb

In This Chapter

  • Declaring members protected

  • Accessing protected members from within the class

  • Accessing protected members from outside the class

Chapter 12 introduces the concept of the class. That chapter describes the public keyword as though it were part of the class declaration — just something you do. In this chapter, you find out about an alternative to public.

Protecting Members

The members of a class can be marked protected, which makes them inaccessible outside the class. The alternative is to make the members public. Public members are accessible to all.


Please understand the term inaccessible in a weak sense. Any programmer can go into the source code, remove the protected keyword, and do whatever she wants. Further, any hacker worth his salt can code into a protected section of code. The protected keyword is designed to protect a programmer from herself by preventing inadvertent access.

Why you need protected members

To understand the role of protected, think about the goals of object-oriented programming:

  • To protect the internals of the class from outside functions. Suppose, for example, that you have a plan to build a software microwave (or whatever), provide it with a simple interface to the outside world, and then put a box around it to keep others from messing with the insides. The protected keyword is that box.

  • To make the class responsible for maintaining its internal state. It's not fair to ask the class to be responsible ...

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