Programming Tutorials

Encapsulation

By: aathishankaran in Java Tutorials on 2007-02-20  

Encapsulation is the mechanism that binds together code and the data manipulates, and keeps both safe from outside interference and misuse. One way to think about encapsulation is as protective wrapper that prevents the code and data from being arbitrarily accessed by the other code defined outside the wrapper. Access to the code and data inside the wrapper is tightly controlled through a well-defined interface. To relate this to the real word, consider the automatic transmission on an automobile. It encapsulates hundreds of bits of information about your engine, such as how much you are accelerating, the pitch of the surface you are on and the position of the shift lever. You, as the user, have only one method of affecting this complex encapsulation: by moving the gear-shift lever. You can't affect the transmission by using the turn signal or windshield wipers,

For example. Thus, the gear-shift lever is a well-defined interface to the transmission. Further, what occurs inside the transmission does not turn on the headlights! Because an automatic transmission is encapsulated, dozen of car manufacturers can implement one in any way they please.

However, from the driver's point of view, they all work the same. This same idea can be applied to programming. The power of encapsulated code that everyone knows how to access it and thus can use it regardless of the implementation details--and without fear of unexpected side effects.

Since the purpose of a class is to encapsulate complexity, there are mechanisms for hiding the complexity of the implementation inside the class. Each method or variable in a class may be marked private are public. The public interface of a class represents everything that external use of the class need to know or may know. The private methods and data can only be accessed by code that is a member of a class. Therefore, any other code that is not a member of a class cannot access a private methods or variable. Since the private members of a class may only be accessed by other parts of your program through the class public method, you can insure that no improper action takes place.