Class and Object

Class
  • A class is simply a representation of a type of object.

  • It is the blueprint/ plan/ template that describe the details of an object.

  • It contains state(instance variables) and behaviour (methods).

  • A template that describes the kinds of state and behaviour that objects of its type support.

Example:-
Class Employee
{
  //code......
}			
Object:-
  • An Object is a real world entity.

  • An object can be considered a "thing" that can perform a set of related activities.

  • The set of activities that the object performs defines the object's behavior.

  • For Example:

    amit is an object of class Employee.
    Employee tkhts = new Employee();
    				


Instance Member and Class Member

Instance Member:-
  • Instance variables are non-static.

  • There is one occurrence of an instance variable in each class instance.

  • It is also known as a member variable or a field.
Example of an instance variable:-
class Employee
{
 int id;
  //code......
  //code......
}

Class Member:-

  • Class variables are called static variables.
  • There is only one occurrence of a class variable per JVM per class loader.
  • When a class is loaded the class variables are initialized.
  • A static variable is used in the singleton Design pattern.
  • A static variable is used with a final modifier to define constants.
Example of a class variable
class Employee
{
  static int id;
  //code......
  //code......
}