BallWorlds

1. CSSE 120 - Fundamentals of Software Development 1
2. Rose-Hulman Institute of Technology
3. Computer Science & Software Engineering

Designing and implementing multple classes: inheritance and interfaces

Part 5: Mover

Learning objectives

After completing all the parts of this lab, you should ...

... Be able to Explain the following concepts:

• The role in software development of:
  • specifications
  • design
  • UML class diagrams
  • documented stubs
• Relationships in UML class diagrams:
  • IS-A (X extends Y)
  • IS-A (X implements Y)
  • HAS-A (X constructs a Y)
  • HAS-A (X refers to Y)
• What it means to:
  • implement an interface
  • extend a class
  • override a method
• The meaning of:
  • The keyword new
  • The keywords this and super
• The visibility modifiers:
  • private
  • protected
  • public
• A method's signature -- what it tells you
• Constructors:
  • When and how constructors are called directly
  • When and how constructors are called from a subclass
  • What constructors should do
  • Why interfaces do not have constructors
• The difference between a class and an instance of a class
• The following patterns:
  • The counting pattern count = count + 1
  • The summing pattern sum = sum + x
  • The toggle pattern blah = !blah
• The value of:
  • A UML class diagram
  • An interface
  • The Java API specification

... Be able to Do the following:

• Read a UML class diagram and:
  • Implement a class from its UML class diagram
  • Implement a hierarchy of classes from a UML class diagram
• Use an IDE (Eclipse) effectively to:
  • Create documented stubs for a class that implements an interface
  • Implement and modify code
  • Carry out functional tests
  • Do unit testing
• Use objects effectively:
  • Construct new objects
  • Use one object to do work on behalf of another object
• Apply the counting and summing and toggle patterns accurately
• Use the Java API specification effectively:
  • To learn about a class that is new to you
  • To apply what you learn
• Implement a class that implements an interface, including:
  • Determine which stubbed methods need to become actual, do-something implementations
  • Determine what fields are necessary or helpful
• Implement a class that extends another class, including:
  • Determine which methods a subclass must override
  • Determine what fields are necessary or helpful
  • Write appropriate constructors for subclasses
  • Use the keywords this and super effectively

Items in bold above are learning objectives for this part of the lab.

Instructions:

Pair Programming

• One partner begins as the "driver", runs Eclipse, and types program code.
• The other partner observes and types answer into the lab report in Angel.
• Both partners should be equal participants in problem solving.
• Don't hesitate to ask questions of classmates and share your learning with them.

Lab report

• When you see a question prefaced by
  Question: blah blah blah ...
  put your answer in your BallWorlds Report (on Angel) for this part.

Time limit

• Most students complete this exercise in 60 to 120 minutes.
• If you find yourself spending much more time than that on this exercise, please see your instructor. (We want to help you avoid getting bogged down.)

Getting Started

What you should learn

• How to open a lab's report
• How to use a lab's report
• Begin to develop the skill of estimating effort in software development
• How to compile and run a program

What you should do

Getting started

1. Skim through this document. Then return to this point.
2. Open your BallWorlds, Part 5 report (on Angel)
3. Question: Who is your partner for this report?
4. Question: About how many minutes do you think it will take you to complete Part 5 of BallWorlds?
   • Comment: You will implement 7 methods plus a constructor and introduce several fields.
5. Question: What time is it now? (Later we will ask you how long you spent on Part 5 of BallWorlds.)

   Reminder: Each time that you see a question in this document prefaced by

   "Question: yada yada ..."

   put your answer in your BallWorlds report (on Angel) at that time.
   • For each Question:, just wait until you reach the question in this document before answering it in your report.
6. Open Eclipse. Update your BallWorlds project from your SVN repository (Team ~ Update), or else check out BallWorlds from your pair's SVN repository if you don't have it on your computer yet.
7. Compile and run BallWorlds. You should see no error messages, except that only Duds and DudsThatMove can be created yet by the BallButtons.

Reviewing Dud and DudThatMoves

What you should learn

• The difference between a class and an instance of a class
• What it means to implement an interface
• How to use one object to do work on behalf of another object
• The meaning of the keyword this
• How to determine what fields are necessary or helpful

What you should do

Reviewing ideas from Dud and DudThatMoves

8. Question: What is the difference between a class and an instance of that class ?
9. Question: What is the difference between an interface and a class that implements that interface ?
10. Question: According to BallWorld's UML class diagram, a Dud has to implement the Animate, Drawable and Relocatable interfaces? What does that tell you?
11. Question: Your Dud's constructor containted a statement like this:

        ballEnvironment.addBall(this);
    
    

    Explain that statement, word by word.
12. Question: What fields did your DudThatMoves have? Why were they necessary?

If any of the above questions are still confusing to you, ask your instructor or an assistant for help NOW -- you will be unable to complete the rest of this exercise without understanding the answers to the above questions.

Thinking Before Doing

What you should learn

• The role of specifications in software development
• The role of a UML class diagram in software development
• How to read a UML class diagram
• IS-A (X extends Y) relationships in UML class diagram
• IS-A (X implements Y) relationships in UML class diagram
• HAS-A (X refers to Y) relationships in UML class diagram
• The value of interfaces in specifying softare

What you should do

Understanding Mover from BallWorld's UML class diagram

13. Briefly review the specifications of the BallWorlds project.
14. Briefly review the UML class diagram for the BallWorlds project.

    Note its color-coding: The six yellow classes are the six classes that you will eventually implement. Those yellow classes extend the abstract Ball class, which in turn implements the three blue interfaces. Thus, your classes must implement those three blue interfaces. The Ball class, and hence each of your classes which extends Ball, have the grey BallEnvironment object. Some of your Ball classes may want to refer to instances of the green classes. So the only part of the UML class diagram relevant to what you will implement are the colored items listed above.

15. Question: According to the above UML class diagram, what class must a Mover extend?
16. Question: According to the above UML class diagram, what interfaces must a Mover implement?
17. Question: Consider the 7 methods that a Mover must implement to satisfy the contracts of the three interfaces that a Mover implements. Of those 7 methods, which two methods must a Mover implement meaningfully (i.e., not merely stubbed) in order to appear on the screen?
18. Question: Consider the 7 methods that a Mover must implement to satisfy the contracts of the three interfaces that a Mover implements. Of those 7 methods, which method must a Mover implement meaningfully (i.e., not merely stubbed) in order to move?
19. Question: According to the above UML class diagram, what class implements both MouseListener and MouseMotionListener (and hence responds to mouse events)?
20. Question: The World responds to a mouse-press by selecting the Ball nearest the mouse (and showing this by turning that Ball red while the mouse is pressed). Of the 7 Ball methods that must be implemented, which one must be implemented in order for this Ball-selection to work correctly?
21. Question: The World responds to a mouse-drag by (repeatedly, throughout the drag) telling the selected Ball to move to the current mouse-point. Of the 7 Ball methods that must be implemented, which one must be implemented in order for this Ball-dragging to work correctly?
22. Question: The World responds to a mouse-left-click (i.e. press and release) by telling the selected Ball to toggle between the paused and not-paused state. (So, if the Ball is acting, it should stop acting; while if it is not acting, it should resume acting.) Of the 7 Ball methods that must be implemented, which one must be implemented in order for this Ball-pause-resume to work correctly?
23. Question: The World responds to a mouse-right-press by telling the selected Ball to kill itself, that is, to have itself removed from its World. Of the 7 Ball methods that must be implemented, which one must be implemented in order for this Ball-suicide to work correctly?

If any of the above questions are still confusing to you, ask your instructor or an assistant for help NOW -- you will be unable to complete the rest of this exercise without understanding the answers to the above questions.

Implementing Mover

What you should learn

• How to implement a class from its UML class diagram
• How to determine which stubbed methods need to become actual, do-something implementations
• How to determine what fields, if any, are necessary or helpful
• How to read a method's signature
• How to implement a method
• How to construct new objects
• How to use the Java API specification to learn about a class that is new to you
• How to apply knowledge gleamed from reading the Java API specification of a class
• The meaning of the keyword this
• How to use one object to do work on behalf of another object

What you should do

Implementing Mover

As you do this part of the exercise:

• Keep in mind the above questions and their answers.
• Look to the Resources above as needed.
• Do pair programming
• Implement by using documented stubs before converting the relevant stubs to actual, do-something implementations
• You need not do any unit tests (although you are welcome to do so), since the visual nature of BallWorlds lends itself to functional tests (i.e., just run BallWorlds and see if the Balls you implement behaves as desired)
• Use the following as an iterative enhancement plan -- implement and test each stage before continuing to the next stage.
• Ask questions as desired!
• Think about how to solve the following problems and understand what you do -- don't just copy-and-paste blindly.

24. Keeping in mind the above (especially think, don't just copy-and-paste and test each stage before continuing to the next stage):

    Augment your BallWorlds project to include a Mover class that extends Ball (not DudThatMoves) and implements Animate, Drawable, Relocatable. A Mover should be able to: Stage 1: Appear on the screen, with any reasonable size and color. It should start in the exact middle of its world (even if its world is resized). Its color should be different from colors of the Ball types that you previously implemented. Stage 2: Move on its own in a straight line (i.e. at a constant velocity). Each Mover should have its own fixed velocity that is set at random when the Mover is constructed. The random velocity should be in any reasonable range that includes all directions (not just the "positive" direction). Stage 3: Be "selectable" by the mouse. To accomplish this, implement the distanceFrom method per its specification. Hint: you do NOT need to know any "formula" for distances! Important: go back to Dud and implement distanceFrom there also. Otherwise, depending on what stub you used for distanceFrom in Dud, a Dud might always be seen as the "closest" ball. Stage 4: Be "draggable" by the mouse. To accomplish this, implement the moveTo method per its specification. Stage 5: Be "pausable" by the mouse. To accomplish this, implement the pauseOrResume method per its specification. Stage 6: Be "killable" by right-clicks of the mouse. To accomplish this, implement the die method per its specification.

Wrapping Up

What you should do

Summary

Perhaps the most important ideas that you saw in Part 3 of BallWorlds are: How to implement a class from its UML class diagram How to construct new objects How to read the Java API specification of a class and apply what you learn The meaning of the keyword this How to use one object to do work on behalf of another object How to determine what fields are necessary or helpful The difference between a class and an instance of a class

25. Question: How many minutes did it actually take you to complete this part of this lab?
26. Question: Compute the ratio of the time you ACTUALLY TOOK to complete this part of this lab to the time you ESTIMATED that you would take. Choose the ratio in the report that is closest to your ratio.
27. Commit your changes to your SVN repository, being sure that any new files are added.
28. Submit your report for this part of BallWorlds.