FUNDAMENTAL CLASS PATTERNS IN JAVA

A class the basic building block of an object-oriented language such as Java is a template that describes the data and behavior associated with instances of that class. The data associated with a class or object is stored in variables; the behavior associated with a class or object is implemented with methods.

THE GENERAL FORM OF A CLASS

A class is declared by use of the class keyword. The classes that have been used up to this point are actually very limited examples of its complete form. Classes can ( and usually do) get much more complex. 

The general form of a class definition is shown here:

 class classname 

{

type instance-variable1;

type instance-variable2;

// ..

type instance-variableN;

type methodname1(parameter-list) 

{

    //body of method

}

type methodname2(parameter-list) {

  //body of method

}

 //..

type methodnameN(parameter-list) {

   // body of method

}

}

A SIMPLE CLASS

Let's begin our study of the class with a simple example.Here is aa class called Box that defines three instance variables:width,height and depth.

class Box

 {

     double width;

   double height;

   double depth;

 }

Example of  class

 /* A program that uses the Box class.

   Call this file BoxDemo.java

*/

class Box

{

double width;

double height;

double depth;

}

// This class declares an object of type Box.

class BoxDemo

{

public static void main9String args[])

{

Box myBox=new Box;

double vol;

//assign values to mybox's instance variables

mybox.width=10;

mybox.height=20;

mybox.depth=15;

//compute volume of box

vol = mybox.width *  mybox.height  *  mybox.depth;

System.out.println("Volume is" +vol);

}

}

To run this program,you must execute BoxDemo.class.When you do,you will see the following output:

Volume is 3000.0