C# 0 The Complete Reference

Triangle( )

 calls 

base

 with the parameters 

w

 and 

h

. This causes the 

TwoDShape( )

 constructor to be called, which initializes 

Width

 and 

Height

 using these 

values.

Triangle

 no longer initializes these values itself. It need only initialize the value 

unique to it: 

Style

. This leaves 

TwoDShape

 free to construct its subobject in any manner 

that it chooses. Furthermore, 

TwoDShape

 can add functionality about which existing 

derived classes have no knowledge, thus preventing existing code from breaking.

Any form of constructor defined by the base class can be called by 

base

. The constructor 

executed will be the one that matches the arguments. For example, here are expanded 

versions of both 

TwoDShape

 and 

Triangle

 that include default constructors and constructors 

that take one argument.

// Add more constructors to TwoDShape.

using System;

class TwoDShape {

  double pri_width;

  double pri_height;

  // Default constructor.

  public TwoDShape() {

    Width = Height = 0.0;

  }

  // Constructor for TwoDShape.

  public TwoDShape(double w, double h) {

    Width = w;

    Height = h;

  }

  // Construct object with equal width and height.

  public TwoDShape(double x) {

    Width = Height = x;

  }

  // Properties for Width and Height.

  public double Width {

     get { return pri_width; }

     set { pri_width = value < 0 ? -value : value; }

  }

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