Classes, objects and methods
Classes, objects and methods
Class is a user defined data type with template that serves to define its properties. Class is a collection of methods and data types of similar types encapsulated together for a specific functionality. Class is description of how to make an object that contains fields and methods . Java incorporates the basic OOPs concepts.
Java is a true object oriented language and therefore the underlying structure of all java programs is classes. Anything we wish to represent in a java program must be encapsulated in a class that defines the state and behaviour of the basic program components known as objects. Classes create objects , and objects use methods to communicate between them. This is all about object oriented programming structure.
Classes provide an efficient method for packing together a group of logically related data items and functions that work on them.
In java the data items are called fields and functions are called methods. Calling a specific method in an object is described as sending the object a message.
Creating an object
An Object in java is a block of memory that contains space to store all the instance variables. Creating an object is also known an instantiating an object.
For example
Rectangle rext1; // declare the object
Rect1 = new rectangle(); // instantiate the object
The first statement declares a variable to hold the object reference and the second one actually assigns the object reference to the variable. The variable rect1 is now an object of the rectangle class.
Note : Each object has its own copy of the instance variables of its class. Any changes to the variables of one object have no effect on the variables of the another . It is also possible to create two or more reference to the same object.
Example : Program illustrating the concept of classes nd objects.
Class rectangle
{
Int length, width; // declaration of method
Void getdata( int x , int y ) // definition of method
{
Length = x .width = y;
}
Intrextarea() // another method
{
Int area = length * width ;
Return(area);
}
}
Class rectarea
{
Public static void main( string args [])
{
Int area1, area2;
Rectangle rect1 = new rectangle(); // Creating objects
Rectangle rect 2 = new rectangle();
Rect.length = 50; // accessing variables
Rect.width = 10 ;
Area1 = rect1.length x rect1.width;
Rect2.getdata(20,30);
Area2 = rect2.rectarea();
systesm.out.println(“Area : “ +area1);
System.out.println(“ area2 = “ + area2);
}
}