WHAT IS A VARIABLE AND WHAT ARE THE TYPES OF VARIABLE IN JAVA..??

INTRODUCTION :

      Hei.. all !! here we are.. !! In this post, I am going to explain the types of variable available..

The variable which is almost common to all programming languages are

•  Local variable and
•  Global variable

WHAT IS A LOCAL VARIABLE..??

        Yeah..  as soon as you read the heading you would have guessed the definition .. (I hope :D ) !! Of course ..your definition is correct.. !!

 The variable which is available locally is called local variable ..!!

 But what does it mean by local ?? :/

Okies.. Lets jump into the example..

EXAMPLE :

Class happy

     {
           public void add( )

                  {

                    int sad = 5 ;

                    System.out.println( “ My num is “ + sad );

                  }

         public static void main(String args[])

            {

              happy ha= new happy( ); // creating an object
              ha.add( ); // accessing the method using object

            }

     }

OUTPUT:

My num is 5.

EXPLANATION:

     Now here.. class name is happy and the method which is present inside it is add ( ) .

Now the variable ‘sad’ is present inside the method add( ) .

    If a variable is present inside any method it is called ‘local variable’. It is locally available to that method alone.

      If any method tries to access the variable then it will throw an error saying the variables and method can’t be accessed directly. The way to access them is to use the object.

      So, in short the variable which is present inside any method is called ‘local varible’.

WHAT IS A GLOBAL VARIABLE..?

    The variable which is declared globally is called ‘global variable’.

       That is,if the variable is declared outside the method it is called global variable

MEMBER VARIABLE:

      There are 3 types of member variable. They are,

• Instance variable
• Static variable and
• Final variable

WHAT IS AN INSTANCE VARIABLE..?

       The variable which is declared inside the class but outside the method is called ‘instance variable’

 EXAMPLE:

  Class Happiest

     {
           int happier = 5 ;

            public void happy( )

             {

                 System.out.println( “ My num is “ + happier );

            }

         public static void main(String args[])

          {

          Happiest ha = new Happiest( );
          ha.happy( );

          }

}

EXPLANATION:

       Here ‘happier’ is the variable here an ‘instance variable’. This variable is declared inside the class ‘Happiest’ but it is declared outside the method ‘happy’

       This ‘ happier’ variable is tooo happy because this is available through out the class.

DIFFERENCE BETWEEN INSTANCE VARIABLE AND LOCAL VARIABLE:

       The main difference between local and instance variable is,

        If the local variable is not initialized it will throw out the error but it we fail to initialize ‘INSTANCE VARIABLE’ it will get initialized on its own.

EXAMPLE:

Class Happiest

     {  
              int happier ;

               public void happy( )

                 {

                    System.out.println( “ My num is “ + happier);

                 }

          public static void main(String args[])

            {

               Happiest ha = new Happiest( );
               ha.happy( );

           }

}

OUTPUT:

0

EXPLANATION:

     The output is 0 and it didn’t throw any error because it is an ‘INSTANCE VARIABLE’.

     If we didn’t initialize or assign any value to it , it will assign the default value 0 for Integer data type and ‘null’ for string datatype.

EXAMPLE FOR LOCAL VARIABLE:

    Class Happiest

       {
           public void happy( )

                {

                   int happier ;

                   System.out.println( “ My num is “ + happier);

                }

         public static void main(String args[])

          {

             Happiest ha = new Happiest( );
               ha.happy( );

         }

    }

OUTPUT:

      Compile time error. The local variable ‘happier’ is without initialization and it will throw error to initialize it.

STATIC VARIABLES:

      Static variables are independent of objects meaning they don’t belong to specific objects.

     Only one copy of ‘static variable’ exists and they will be shared among all of the objects.

      Static variables are rare . They are unique and have more demand and so only copy exists for a class ; )

DOES STATIC VARIABLE HAVE AN ALTERNATE NAME.. ??

       Yes … static variable is also called as ‘CLASS VARIABLE’ as they belong to the entire class  and not to any specific object.

       The static variable won’t see any partiality .It wont think like.. Oh..man !! This object looks good and polite and so I will be available only to them…” :D

      Instead.. I am one and I will be available to all the objects. There is no partiality when it comes to availability is what this ‘static variable’ thinks..

EXAMPLE:

class StaticExample

    {

         static int count=0;

         public void increment()

           {

             count++;

           }

       public static void main(String args[])
         {

             StaticExample obj1=new StaticExample();

              StaticExample obj2=new StaticExample ();

              obj1.increment();

               obj2.increment();

               System.out.println("Obj1 count is="+obj1.count);

             System.out.println("Obj2 count is="+obj2.count);

        }

   }

OUTPUT:

Obj1 count is = 2

Obj2 count is= 2

EXPLANATION:

       Look at the above code.. obj1 and obj2 are the 2 objects created for the class StaticExample.

         When the method increment ( ) is called for the first time ie. obj1.increment ( ) then the method gets called and increments the value of the “count “

         The value of the count is now 1.

NOTE: COUNT IS A STATIC VARIABLE and so only one copy of the variable exists.

       Then when the same method is called using DIFFERENT OBJECT the value is incremented again and now the value of the count now turns to 2.

BIT COMPLEX EXAMPLE:

Class staticexample
      {
           static int X= 10;
           int Y=5; // non static variable
           public static void main(String [] args)
              {
                    staticDemo instance1 = new StaticDemo();  // creating object for a class

                    staticDemo instance2 = new StaticDemo();  // creating another object for a class
                    //printing the value of x and y using 1st object

                    System.out.println("instance1.X=" + instance1.X+ "instance1.Y="+instance1.Y); 
                    //printing the value of x and y using 1st object

                     System.out.println("instance2.X=" + instance2.X+ "instance2.Y="+instance2.Y); 

                     instance1.X=15; // changing the value of x and y

                     instance1.Y=10;

            System.out.println("After updating X value to 15 and Y value to 10 from instance1 : ");

            System.out.println("instance1.X="+instance1.X+"instance1.Y="+instance1.Y "); //explained below

          System.out.println("instance2.X="+instance2.X+"instance2.Y="+instance2.Y "); 
//explained below
               }
          }

    OUTPUT:

        instance1.X = 10 instance1.Y=5
        instance2.X = 10 instance2.Y=5
        After updating X value to 15 and Y value to 10 from instance1:
        instance1.X=15 instance1.Y=10
        instance2.X=15 instance2.Y=5

  Initially the values are 10 and 5 .

  Then the object ‘instance 1’ is accessing the variable x and y and trying to change the values.

  It is changing the value of x and y to 15 and 10.

  Note that for static variable there is only one copy and so when any changes happen to it will be reflected to all the objects.

   So the variable x erases its previous memory 10 and now updates its new value 15. 

   But lucky variable ‘Y’ has made  itself change its value only for object ‘instance 1’ ie. So, instance 1 has the variable value Y = 10 and instance 2 =5.

   Wow.. Instance 2 has the value Y= 5 and not 10 which is the updated value because Y is normal variable and only the instance 1 object has changed its variable’s value and not the instance 2.

When value changes to 15 then the initial value will get deleted from the variable’s memory and so VALUE = 15 will be available to both the objects where as for NORMAL VARIABLE

                                                     

                                                                                                                                   

                       A copy of variable is available to each object and note we are changing the value of variables that is belonging to object instance1 and so the values resides within that object itself

                     Unless until the variable is static, each object will have its own set of values.

FINAL VARIABLES:

        When we apply "final" keyword to a variable,the value of that variable remains constant. (or) Once we declare a variable as final,the value of that variable cannot be changed.

EXAMPLE:

  Class Ex
   {
        public final int a= 10;

          public void add()

              {

                  Int a= 12;

                  System.out.println(“the value of a = “ +a);

              }

   

      public static void main(String args[])

       {

        Ex e = new Ex( );
        e.add( );

       }

OUTPUT:

Compile time error.

EXPLANATION:

     This is because we are trying to change the value of ‘a’ inside the method.

     ‘a’ is a final variable and so it can’t be changed.

DIFFERENCE BETWEEN STATIC AND FINAL KEYWORD:

      When a variable is declared ‘STATIC’ only one copy exists and it belongs to entire class .

       Whereas when a  FINAL VARIABLE is used then the value of a variable cannot be changed inside the program no matter what.

CONCLUSION:

        So, that's it for this post. We have seen a lot more about variable. I am sure you people will be clear about the concepts. If you have any doubts, post in the comments below. Your feedback is welcomed. Help me improve this blog with your valuable feedback. Hit like button and share this post if you find it useful. Have a pleasant day :)