private: you can't touch that

private: you can't touch that!

The private keyword that means no one can access that member except that particular class, inside methods of that class. Other classes in the same package cannot access private members, so it's as if you're even insulating the class against yourself. On the other hand, it's not unlikely that a package might be created by several people collaborating together, so private allows you to freely change that member without concern that it will affect another class in the same package. The default "friendly" package access is often an adequate amount of hiding; remember, a "friendly" member is inaccessible to the user of the package. This is nice, since the default access is the one that you normally use. Thus, you'll typically think about access for the members that you explicitly want to make public for the client programmer, and as a result, you might not initially think you'll use the private keyword often since it's tolerable to get away without it. (This is a distinct contrast with C++.) However, it turns out that the consistent use of private is very important, especially where multithreading is concerned. (As you'll see in Chapter 14.)

Here's an example of the use of private:

This shows an example in which private comes in handy: you might want to control how an object is created and prevent someone from directly accessing a particular constructor (or all of them). In the example above, you cannot create a Sundae object via its constructor; instead you must call the makeASundae( ) method to do it for you.

Any method that you're certain is only a "helper" method for that class can be made private to ensure that you don't accidentally use it elsewhere in the package and thus prohibit you from changing or removing the method. Making a method private guarantees that you retain this option. (However, just because the handle is private doesn't mean that some other object can't have a public handle to the same object. See Chapter 12 for issues about aliasing.)