C# 0 The Complete Reference

The this Keyword

Before concluding this chapter, it is necessary to introduce 

this

. When a method is called, 

it is automatically passed a reference to the invoking object (that is, the object on which the 

method is called). This reference is called 

this

. Therefore, 

this

 refers to the object on which 

the method is acting. To understand 

this

, first consider a program that creates a class called 

Rect

 that encapsulates the width and height of a rectangle and that includes a method 

called

Area( )

 that returns its area.

using System;

class Rect {

  public int Width;

  public int Height;

  public Rect(int w, int h) {

    Width = w;

    Height = h;

  }

  public int Area() {

www.freepdf-books.com

---

134

 

P a r t   I :  

T h e   C #   L a n g u a g e

    return Width * Height;

  }

}

class UseRect {

  static void Main() {

    Rect r1 = new Rect(4, 5);

    Rect r2 = new Rect(7, 9);

    Console.WriteLine("Area of r1: " + r1.Area());

    Console.WriteLine("Area of r2: " + r2.Area());

  }

}

As you know, within a method, the other members of a class can be accessed directly, 

without any object or class qualification. Thus, inside 

Area( )

, the statement

return Width * Height;

means that the copies of