Classes

         The class is at a core of Java. It is a logical construct upon which the entire Java language is built. It defines the shape and nature of an object. A class forms the basis of OOP’s in Java. It provides you to Encapsulate data and code into a single unit. Once a class has been created, you can create as many objects as you want for the class. Infect objects are variables of the type ‘ class’.

Syntax:

class class_name

{

data type inst_var-1:

data type inst_var-2:

…………………….

return_type Method_name1([args])

{

………………..

}

return_type Method_name2([args])

{

………………….

}

…………………….

}

class Box

{

double height;

double width;

double depth;

}

Note: class : A reserved keyword, which allows you to, builds a class and which defines the shape and nature of the object. class_name : Specifies a name given to the entire design. data_type instance variable : Referred as data members. Method_name : Pieces of codes that manipulate the instance variables commonly referred as methods or member methods.

Collectively the instance variables and member methods are called the members of the class.

Creating objects:

         A class just provides you with a template. Once a class has been created the next step would create variables of type “class”. Objects can be created in the following format

Syntax: class_name object_name = new class_name();

Where class_name is the name of the class.

Where object_name is the name of the object.

Where new is the dynamic memory allocator.

Where class_name() is the default constructor.

Example: Box B = new Box();

Accessing instance variable:

         Once an object has been created, you can access the instance variables of the object using the notation.

Syntax: Object_name.instance_variable

Example:

B.width;

B.height;

B.depth;

Example:

 

class Box{ double width; double height; double depth; }class App14{ public static void main(String yck[]) { Box b=new Box(); b.width=10; b.height=20; b.depth=30; double vol=b.width*b.height*b.depth; System.out.println(“The volume of the box is : “+vol); } }

 

output:

\>javac App14.java

\>java App14

The volume of the box is : 6000.0

Accessing Methods of an object:

         Just like you access the instance variables. You can also access methods from outside the class using the following notation.

Syntax: object_name.method_name([arguments]);