Keyword this

In certain cases, the method is sometimes necessary to refer to object that has it. To allow this, Java provides keyword this. Keyword this is actually a reference to the object that is currently active. Consider the following code:

class Box {
   
   double length, width, height;

   //constructor
   Box(double l, double w, double h) {
      length = l;
      width = w;
      height = h;
   }
}

Actually, the above code can also be written using reference this, as follows:

class Box {
   
   double length, width, height;

   //constructor
   Box(double l, double w, double h) {
      this.length = l;
      this.width = w;
      this.height = h;
   }
}

For the case above, the presence of keyword this is actually going to be a little inconvenient and can be said to be unnecessary. However, in other contexts, the use of keyword this is actually required. As proof of this statement, you try to take a good look at the explanation below.

As we all know, Java does not allow us to declare variable with the same name within a block. On the other hand, Java allows us to declare name of the same parameter as the name of the data contained in the class. Nevertheless, the name of a local variable (in this case, the variable used as a parameter) will overwrite with the name of the data contained in the class. To avoid overwriting process variable, then we must use keyword this, as shown in the following code:

class Box {

   double length, width, height;

   //constructor
   Box(double length, double width, double height) {
      this.length = length;
      this.width = width;
      this.height = height;
   }
}

Here, this.length, this.width, and this.height refer to data length, width, and height contained in the class Box, not refer to parameters contained in the constructor.