Programming Tutorials

Object-Oriented Programming

By: aathishankaran in Java Tutorials on 2007-02-01  

Object-oriented programming is at the core of java. In fact, all java programs are object-oriented this isn't an option the way that it is in C++, for example. OOP is so integral to java that you must understand it basic principles before you can write even simple java programs. Therefore, this chapter begins with a discussion of the theoretical aspects of OOP.

Two paradigms

As you know, all computer programs consist of two elements: code and data. Furthermore, a program can be conceptually organixed around its code or around its data. That is, some programs are written around 'what is happening' and others are written around 'who is being affected.' These are the two paradigms that govern how a program is constructed. The first way is called the process-oriented model. This approach characterizes a program as a series of linear steps (that is, code). The process-oriented model can be thought of as code acting on data. Procedural languages such as C employ this model to considerable success. However, as mentioned in the previous article, problems with this approach appear as programs grow larger and more complex.

To manage increasing complexity, the second approach, called object-oriented programming, was conceived. Object-oriented programming organizes a program around its data (that is, objects) and a set of well-defined interfaces to that data. An object-oriented program can be characterized as data controlling access to code. As you will see, by switching the controlling entity to data, you can achieve several organizational benefits.


An essential element of object-oriented programming is abstraction. Humans manage complexity through abstraction. For example, people do not think of a car as a set of tens of thousands of individual parts. They think of it as a well-defined object with its own unique behavior. This abstraction allows people to use a car to drive to the grocery store without being overwhelmed by the complexity of the parts that form the car. They can ignore the details of how the engine, transmission, and braking systems work. Instead they are free to utilize the object as a whole.

Hierarchical abstractions of complex systems can also be applied to computer programs. The data from a traditional process-oriented program can be transformed by abstraction into its component objects. A sequence of process steps can become a unique behavior. You can treat these objects as concrete entities that respond to messages telling them do something. This is the essence of object-oriented programming.

Object-oriented concepts form the heart of java just as they form the basis for human understanding. It is important that you understand how these concepts translate into programs. As you will see, object-oriented programming is a powerful accompanying the life cycle of any major software project, including conception, growth and aging. For example, once you have well-defined objects and clean, reliable interfaces to those objects, you can gracefully decommission or replace parts of an older system without fear.

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