Java Basics

class  is  design  to specify the  attributes  and   behavior of  object .Attributes of an object are implemented using
variables and the behaviors of  an  object  are implemented using methods

## Variables --    instance  variables  , instance  attributes
                             Store state of an object .
                             each object  has its own copy of instance variable .Define  inside  class  and  outside all  methods .
                   
                             class variable , static variable - Single copy of  variable is  shared  among  all objects .
                   
                   
##  Methods   --   instance methods , are manipulate instance  variables
                             class methods , static  methods  , are can be  used  to  manipulate static methods
                   
##  Constructors -- used to create and initialize objects of a class                    

##  Packages  --  allows  to  group together a related set  of classes and  interfaces .
                            package  names , should  be  in  lower case
               
##  Import    --  import statement doesn't embed the content of  the  imported class  in  our  class .So  importing more classes
                  doesn't  increase size of our  class .
                  when importing  multiple classes  with  same  name
                 
                  java.util.Date date1 ;
                  java.sql.Date  date2 ;
                 
##  access modifiers - control accessibility of  class and its members outside the class and package .
##  non access modifier - changes  default  behavior of  class  and  its  members .
    abstract , static , final , synchronized , native , strictfp , transient , volatile

## final modifier can't be used with the declaration of an interface.
   class that is marked final can't be extended by another class .
   final variable can't  be reassigned a value . It can be assigned a value only once.
  
   If a reference variable is defined as a final variable ,we can 't  reassign another object to it .
   But we can call methods on this variable (that modify its state)
  
   final method defined in a base class can't be overridden by a derived class .
  
## static variables belong to  a class .
   They 're common to  all instances of  class and aren't unique to any instance of  a class.
   static attributes exist independently of any instances of  a class and may be accessed even when no instances
   of the class have been created

   static methods aren't associated with objects and can't use any  of the instance variables
   of  a class.
  
   It  is common practice to use static methods to define utility methods , which are methods that usually
   manipulate the method parameters to compute and return appropriate value.
  
        static double interest (double num1 , double num2 , double num3){
            return (num1 + num2)
        }
  
  
   static  final  int variableConstantName = 6;