Problems for Session O2: Inheritance

Note: Most of these problems require conditionals.

Problem O2-A: Extending Points

Build ComparablePoint, a subclass of the Point class that includes equals(Point other) and lessThan(Point other) methods. The equals method should return true if the other point is equal to the current point. The lessThan method should return true if the current point is closer to the origin than the other point.

Write a small test program that uses your ComparablePoints.

Problem O2-B: Putting Points on a grid

Build GridPoint, a subclass of the Point class that puts points on a grid, rather than anywhere on the plane. For example, if the grid has a spacing of 1, then the point (0.7,2.3) is placed at (1,2). If the grid has a spacing of 0.5, then the point (1.2, 2.3) is placed at (0.5, 2.5). The constructor for your class should take the spacing as a parameter.

Write an appropriate program to test your new class.

Problem O2-C: Validating Squares

One of the drawbacks to the Square and Rectangle classes we developed in the experiments is that they do not verify that their width and height are reasonable. In particular, they will admit negative or zero-valued widths and heights, something we traditionally do not accept for squares and rectangles.

a. Develop a new SafeSquare class that extends the Square class.

b. Develop a new SafeRectangle class that extends the Rectangle class. Extend SafeRectangle to build a NewSafeSquare class.

c. Which of a and b is a better way of building a safe square class?

Problem O2-D: A hierarchy of shapes

Often, we use subclassing to build hierarchies of objects. For example, we might begin with Books, subclass them to Textbooks, Novels, and Collections (obviously not a comprehensive list of types of books). We could then subclass Textbooks to Introductory and Advanced or perhaps by discipline. Similarly, we might subclass Collections into ShortStories and Essays or perhaps into single author and multiple author collections. And so on and so forth.

Design a hierarchy of shapes. That is, begin with a generic Shape class including notes as to which methods it might provide, such as area. Then list the subclasses and sub-subclasses of the Shape class. At each stage, note which methods you may need to override.