this is reference example for this keyword:

class Demo {
        int a;

      public Demo(){
          this(2);  // this is refer to parametrized constructor
         }

     public Demo(int a) {
          System.out.println("this is parametrized constructor');
       }
   public void display(){
       this.a=10;            // calling instance variables 
     } 

   public void show(){
       this.display(); // calling instance methods 
    } 

    }