this in java

this is a keyword in Java.It can be used inside the method or constructor of  Class.Within an instance method or a constructor, this is a reference to the current object — the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this.

Here are the points where the keyword this can be used in Java :

•  Within the method of current class.
•  Within the constructor of current class.
•  To refer current class instance variable.
•  Passed as arguments to call constructor.
•  Passed as arguments to call method.
•  To invoke the method of current class.
•  To invoke the constructor of current class. 

 Example :
   
       1.  Without this
          
                // one class needs to have a main() method
                 public class HelloWorld
                  {
                    public static void main(String[] args)
                       {
                         // create an instance of class "OtherClass"    
                        OtherClass myObject = new OtherClass("Hello World!");
                        //  call the method  of class "OtherClass"
                        myObject.display();
                       }
                   }

                public class OtherClass
                 {
                    private String message;
                    public OtherClass(String message)
                      {
                           message = message;
                      }
                    public void display(){
                       System.out.print("message : "+message);
                    }
                } 

           Output :  
                  message : null

                 Here the out is null because the name of instance variable (message)and local  variable (message) is same .  To distinguish this two variable we should use the this keyword . Here are the program . 

      2. With this
          
               // one class needs to have a main() method
            public class HelloWorld
             {
                public static void main(String[] args)
                 {
                   // create an instance of class "OtherClass"    
                  OtherClass myObject = new OtherClass("Hello World!");
                  //  call the method  of class "OtherClass"
                  myObject.display();
                 }
             }

            public class OtherClass
             {
                  private String message;
               public OtherClass(String message)
                {
                      this.message = message;
               }
              public void display(){
                  System.out.print("message : "+message);
               }
           } 

 Output :  
                  message : Hello World!




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