Class and Object

Class and Object

üA class defines a new data type. This new data type is used to 

create objects of that type.

üA class is a template for an object and an object is an instance 

of a class.

Creating Objects

üObtaining objects of a class is two steps process:

  1. Declare a variable of the class type.

  2. Acquire an actual, physical copy of the object and assign it to that variable.

ü To allocate a physical memory new() is used. It 

dynamically allocates memory for an object and returns a 

reference to it.

üIn Java, all class objects must be dynamically allocated.

A Simple Example

class Box

{

  double width;

  double height;

  double depth;

}

class BoxDemo

{

  public static void main( String args[])

  {

  Box mybox, mybox1;

  mybox = new Box();

  mybox1 = new Box();

  mybox.width=10;

  mybox.height = 20;

  mybox. depth = 15;

  mybox1.width = 10;

  mybox1.height = 25;

  mybox1.depth=5;

  }

}

A Simple Example- Some points

üMembers are linked to an object using dot (.) operator.

üEach object contains its own copy of each instance 

variables defined by the class.

üThe java compiler automatically puts each class into it’s own .class file.

  - For this example, two .class files:

  1. Box.class

    2. BoxDemo.class

new() is used to dynamically allocate memory for an object.