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2.4 Constructor chaining

  1. Change the code of the constructor with signature Circle(double radius) as follows:

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    public Circle(double radius) : this(radius, 0, 0, "white")
{
}

    Note that this(radius, 0, 0, "white") calls the all-args constructor within the class. The default values for centerX, centerY, and color are passed.

  2. Change the code of the default constructor Circle() as follows:

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    public Circle() : this(1)
{
}
    • this(1) now refers to the constructor with signature Circle(double radius) within the class. The default value for radius is passed.
    • The most generic constructor (the default constructor) calls the more specific constructor, which in turn calls the most specific constructor (the all-args constructor).
    • Note that every default value is determined in only one place.

  3. Modify the code in the Main method as follows: 

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    Circle myAllArgsCircle = new Circle(3, 1, 4, "green");
Console.WriteLine(myAllArgsCircle.CalculatePerimeter());
Console.WriteLine(myAllArgsCircle.CalculateArea());

Circle myDefaultCircle = new Circle();
Console.WriteLine(myDefaultCircle.CalculatePerimeter());
Console.WriteLine(myDefaultCircle.CalculateArea());

Circle myRadiusCircle = new Circle(6);
Console.WriteLine(myRadiusCircle.CalculatePerimeter());
Console.WriteLine(myRadiusCircle.CalculateArea());

  4. Run your program. Your output will look like this: 

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    18.84955592153876
28.274333882308138
6.283185307179586
3.141592653589793
37.69911184307752
113.09733552923255

    Note that the output is the same as in Exercise 1.3.

  5. Try some other values and view the output.

The constructors still take numeric centerX and centerY (design 1). See Three ways to give a Circle a centre.