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4.2 Inheritance: the Shape class

  1. Continue with the project from the previous chapter. It contains the classes as you left them there.

  2. Create a new class Shape according to the following class diagram:

    Shape base class with protected colour, default colour constant, virtual area and perimeter, DescribeSize and static Definition Shape base class with protected colour, default colour constant, virtual area and perimeter, DescribeSize and static Definition

    + means public
    - means private (not used here)
    # means protected (available to the class and all derived classes)
    <<constant>> means constant field (PascalCase per C# conventions)
    Underlined means static
    In UML, virtual operations are often shown in italic; in C#, CalculateArea() and CalculatePerimeter() are declared virtual so derived classes can override them.

    Use the following extra information:
    - The default value for color is "white" and since the default value is used in more than one place, make it a constant;
    - Use constructor chaining;
    - A shape is a collection of points;
    - The perimeter is unknown, so return 0;
    - The area is unknown, so return 0;
    - The DescribeSize() method is identical to that of the Circle and Rectangle classes;
    - Add the getter and setter for color;

  3. Note: The Definition() method is static. It therefore cannot be overridden in the derived classes. You can redefine a static method within the derived classes.

    • The three attributes are protected and therefore available to the derived classes;
    • The methods CalculatePerimeter() and CalculateArea() are public. However, they will be overridden in the derived classes;
    • The methods Shape(string color), Shape() and Definition() are public, because they say something specific about the Shape class;
    • The method DescribeSize() is public. This method will disappear from the derived classes.