• In java, it is illegal to declare two local variables with the same name inside the same or enclosing scopes.
• But you can have formal parameters to methods, which overlap with the names of the class' instance variables.
• this keyword is used to refer to the current object.
• this can be used to resolve any name collisions that might occur between instance variables and formal variables.
• When a formal variable has the same name as an instance variable, the formal variable hides the instance variable.
•  Also used in method chaining and constructor chaining.

// instance and formal variables are different

class Box{
  double w=5,h=5,d=5;
  Box(double w1,double h1,double d1){
      w=w1;
      h=h1;
      d=d1;
  }
  double volume(){
      return w*h*d;
  }
 }
 class BoxTest1{
   public static void main(String args[]){
       Box b=new Box(1,2,3);
       System.out.println("Volume is: " b.volume());
  }
 }

Output:
Volume is: 6.0

// instance and formal variables are same
 

class Box{
   double w=5,h=5,d=5;
   Box(double w,double h,double d){
        w=w;
        h=h;
        d=d;
   }
   double volume(){
        return w*h*d;
   }
  }
  class BoxTest2{
    public static void main(String args[]){
         Box b=new Box(1,2,3);
         System.out.println("Volume is: " b.volume());
   }
  }

Output:
Volume is:125.0
 

// 'this' hides the instance variables

class Box{
   double w=5,h=5,d=5;
   Box(double w,double h,double d){
       this.w=w;
       this.h=h;
       this.d=d;
 }
  double volume(){
       return w*h*d;
  }
 }
 class BoxTest2{
   public static void main(String args[]){
      Box b=new Box(1,2,3);
      System.out.println("Volume is: " b.volume());
  }
 }

Output:
Volume is:6.0
 

// method chaining

class Fchain{ 
        int a,b;
        Fchain setValue(int x,int y){
                a=x;
                b=y;
                return this;
        }
        Fchain disp(){
               System.out.println("a value is:" a);
               System.out.println("b value is:" b);
               return this;
        }
 }
 class FchainDemo{
        public static void main(String args[]){
        Fchain f1=new Fchain();
        f1.setValue(10,20).disp().setValue(11,22).disp();
        }
 }

//Constructor Chaining

class Test{
         int a,b,c,d;
         Test(int x,int y){
                   a=x;
                   b=y;
         }
          Test(int x,int y,int z){
                   this(x,y);
                   c=z;
         }
         Test(int p,int q,int r,int s){
                   this(p,q,r);
                   d=s;
         }
          void disp(){
     System.out.println(a %u201D %u201D b %u201D %u201D c %u201D %u201D d);
         }
 }


 class TestDemo{
      public static void main(String args[]){
          Test t1=new Test(10,20,30,40);
          t1.disp();
          }
 }