Class & Object

 Creating and using class

• A class is a user defined data type.
• Once the class has been defined, we can create “variables” of that type using declarations that are similar to the basic type declarations.
•  In java, these variables are termed as instances of classes, which are the actual objects.
•  The syntax of class definition is as follow:

      class class name[extends superclassname]

    {

               [fields declaration; ]

              [methods declaration; ]

    }

•  Everything inside the square bracket is optional.
•  Classname and superclassname are valid java identifier.
•  The keyword extends indicates that the properties of superclass is extended.

        Examle:

         Class rect

        {

               int length;

               int width;

              void getdata(int x,int y)

             {

                      length=x;

                      width=y;

             }

             int rectarea()

           {

                   int area=length*width;

                  return(area);

          }

       }

Creating Objects

•  An object in java is essentially a block of memory that contains space to store the instance variables.
•  It is also known as instantiating an object.

Example:

    rectangle r1; //declare the object

    r1=new rectangle();//initiate the object

•  The first statement declares a variable to hold the object reference and second one actually assign the objects reference to the variable.

•  We can also combine both statement.

    rectangle r1=new rectangle();