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Trail: Learning the Java Language

Lesson: Object-Oriented Programming Concepts


Under Construction: We are in the process of updating and rewriting this lesson. Some sections are incomplete and are marked with [PENDING]. Continue to use our feedback form(in the Learning the Java Language trail) to tell us what you like and don't like about this lesson and the tutorial.

If you've never programmed using an object-oriented language before, you need to understand what objects and classes are and how these concepts translate to code.

This lesson provides the conceptual basis for object-oriented languages in general. The last section shows you how these general concepts translate into code for an applet written in the Java programming language.

What Is an Object?(in the Learning the Java Language trail)

An object is a software bundle of related variables and methods. Software objects are often used to model real-world objects you find in everyday life.

What Is a Message?(in the Learning the Java Language trail)

Software objects interact and communicate with each other using messages.

What Is a Class?(in the Learning the Java Language trail)

A class is a blueprint or prototype that defines the variables and the methods common to all objects of a certain kind.

What Is Inheritance?(in the Learning the Java Language trail)

A class inherits state and behavior from its superclass. Inheritance provides a powerful and natural mechanism for organizing and structuring software programs.

What Is an Interface?(in the Learning the Java Language trail) [PENDING]

An interface is a contract in the form of a collection of method and constant declarations. When a class implements an interface, it promises to implement all of the methods declared in that interface.

How Do These Concepts Translate into Code?(in the Learning the Java Language trail)

This section looks at a small applet, and shows you the code that creates objects, implements classes, sends messages, establishes a superclass, and implements an interface.

Questions and Exercises: Object-Oriented Concepts(in the Learning the Java Language trail)

Test your understanding of objects, classes, messages, and so on by doing some exercises and answering some questions.

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