Object Orientation in Java 

• Okay, so now that we understand the most basic Java syntax it is time to learn how object-oriented design is implemented in Java. 

• The basic unit of object-orientation in Java is the class. The class is often described as a blueprint for an object. It allows a programmer to define all of the properties and methods that internally define an object, all of the API methods that externally define an object, and all of the syntax necessary for handling encapsulation, inheritance and polymorphism. 
• When a virtual machine needs to create an actual object from the class' blueprint, it is said to create an an instance of the class or to instatiate an object. Thus, the blueprint is used to actually create an object which is stored in the computer's memory. The object will actually be able to utilize the methods and fields defined by its class. 

• It is also important to know that more than one instance can be fabricated from the same class during the execution of a program. What's more, each of these instances has its own copy of methods and fields so that over the life of the program each can grow independently. 
• Thus, for example, a Button class might be used to instantiate two buttons in a program. Once instantiated, each Button object has its own label field and background color field. During the program, one button might be set to be Blue and to say "Hello Cyberspace". Another might be set to red and "Hello Selena." Both remain Button objects, but they gain unique features.

You can compare two objects to see if they are built from the same class by using the "instanceof" keyword such as in the following example: if (someObject instanceOf Button)   {   ...do something....   }

Additional Resources:

• Learning to Write Java 
• Introducing Java (TM) - Your First Applet 
• Java FAQs 
• Java Software 
• java.sun.com 
• Sun Microsystems

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