Articles : JavaBoutique's Introduction to Java :
Object-Oriented Design :

Encapsulation

The beauty of objects is that you can use them even if you don't know how they work inside. As we said before, objects are "little black boxes of functionality". So what does that mean exactly?

Well, that means that nobody but the object itself needs to know anything about how its properties and methods are defined and implemented. This is called "encapsulation" and is the cornerstone of good OOD.

Are the list of items stored in an array or a vector? How is sorting handled, with a quick sort or a bubble sort? How is a selection marked and how do you handle multiple selections?

Encapsulation means that the answers to all these questions are private, known only by the object itself.

What is the benefit of this?

Well, the benefit is that if I want to use a Select Box, I do not need to deal with all of the complex code that handles all of the functionality of a select box. Instead, I just put the self-contained select box object in my application and use it.

This is an incredibly useful concept because it means that it is far easier to modify and understand code because you only need to deal with small pieces of code at any one time. As a developer, I do not need to deal with the intricacies of select box functionality, I just use the thing!

It is also a good metaphor for the real world, that can be thought of as being made up of encapsulated objects.

Consider the computer you are using to read this. Do you know how the CPU works? Most likely you don't. But that is fine. It works regardless. And the fact that you don't have to spend time learning electrical engineering means that you are free to spend your time building things "using" the CPU.

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Selena Sol contributes to the JavaBoutique's Introduction to Java. Selena curently works for Barclays Capital in London, one of the leading global investment banks in Europe and has worked as a software developer for the National Center for Human Genome research, Microline Software, Neuron Data, and Electric Eye in Singapore. Selena is perhaps best-known for creating the Public Domain Web Script Archive (Extropia) and writing several books on Web Programming (Perl, CGI, Java).
Email: selena@extropia.com

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