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Outline of this exercise

Outline of this exercise. Learning objectives: After this exercise, a student should be able to: Read a UML class diagram Describe the basic process for developing a UML class diagram Explain what is easy about the process and what is hard Explain the iterative nature of the design process

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Outline of this exercise

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  1. Outline of this exercise • Learning objectives: • After this exercise, a student should be able to: • Read a UML class diagram • Describe the basic process for developing a UML class diagram • Explain what is easy about the process and what is hard • Explain the iterative nature of the design process • Process: • Review the specification of BallWorld • Develop a UML class diagram for BallWord • Together (in groups), step by step

  2. Specification of BallWorld • BallWorld is just that -- a world that contains various kinds of balls • along with hotspots and perhaps other things eventually • Each of the buttons represents a Java class that you will write • Pressing a button creates a ball of that type • Types of Balls might include: • Dud: does nothing • DudThatMoves: just moves in a constant, random velocity • Dragger: the user can drag it around and kill (delete) it • Mover: like a Dragger, but moves like a MovingDud • Bouncer: like a Mover, but bounces off the walls of the World • Shrinker: A Bouncer that grows and shrinks in size • Exploder: Grows, then explodes and replicates itself! Questions? You cannot design software unless you know what it is supposed to do!

  3. Design BallWorld, by drawing a UML class diagram for it Review the specification, then: • Identify kinds of objects – these become classes • Identify relationships between classes • is-a (extends), is-a (implements), has-a • Identify interfaces that specify what is needed for the classes to relate • For each class, determine its attributes and operations • For each class, for each attribute/operation, determine its type We frequently retrace our steps and fine tune our design.

  4. List the classes in BallWorld • List the kinds of things – classes – that you think belong in the BallWorld design: • Some are visual • Some are internal • Some are relevant Java library classes like JFrame • When done, compare your list with other lists around the room

  5. The classes that I chose • Visual things: • BallWorldFrame • WorldPanel • ButtonsPanel • BallButton • A single class, with several instances with different labels • Non-visual things: • BallWorld • The class that contains main • Ball • Various subclasses of Ball • HotSpot • World • The class that manages all the Balls and HotSpots • Relevant Java library classes: • JFrame • JPanel • JButton Question: Why not just let the WorldPanel play this role? Answer: I choose to separate function from display of that function

  6. Design BallWorld, by drawing a UML class diagram for it We just did our first iteration of Step 1 Review the specification, then: • Identify kinds of objects – these become classes • Identify relationships between classes • is-a (extends), is-a (implements), has-a • Identify interfaces that specify what is needed for the classes to relate • For each class, determine its attributes and operations • For each class, for each attribute/operation, determine its type Now we’ll do our first iteration of Step 2, beginning with the is-a (extends) relationship We frequently retrace our steps and fine tune our design.

  7. Draw the is-a relationships between the classes shown Notation: A is-a B, that is, A extends B This means that A inherits all the attributes (data) and operations (behaviors) of B A B Is-arelationships JButton BallButton JFrame ButtonsPanel JPanel BallWorldFrame BallWorld WorldPanel Ball HotSpot World

  8. Draw the is-a relationships between the classes shown Notation: A is-a B, that is, A extends B This means that A inherits all the attributes (data) and operations (behaviors) of B A B Is-arelationships JButton JFrame BallButton JPanel BallWorldFrame BallWorld ButtonsPanel WorldPanel Ball World HotSpot Questions on is-a so far?

  9. Draw the is-a relationships between the types of Balls Notation: A is-a B, that is, A extends B This means that A inherits all the attributes (data) and operations (behaviors) of B A B Is-arelationships • Types of Balls might include: • Dud: does nothing • MovingDud: just moves in a constant, random velocity • Dragger: the user can drag it around and kill (delete) it • Mover: like a Dragger, but moves like a MovingDud • Bouncer: like a Mover, but bounces off the walls of the World • Shrinker: A Bouncer that grows and shrinks in size • Exploder: Grows, then explodes and replicates itself! Ball Mover Dud Shrinker Dragger Exploder MovingDud Bouncer . . .

  10. Draw the is-a relationships between the types of Balls Notation: A is-a B, that is, A extends B This means that A inherits all the attributes (data) and operations (behaviors) of B A B Is-arelationships • Types of Balls might include: • Dud: does nothing • MovingDud: just moves in a constant, random velocity • Dragger: the user can drag it around and kill (delete) it • Mover: like a Dragger, but moves like a MovingDud • Bouncer: like a Mover, but bounces off the walls of the World • Shrinker: A Bouncer that grows and shrinks in size • Exploder: Grows, then explodes and replicates itself! Ball Mover Dud Shrinker Dragger Exploder MovingDud Bouncer . . . Questions on is-a relationships?

  11. Draw the has-a relationships in which objects are created, for the classes shown Notation: A has-a B, here, A creates a B Indicate the multiplicity on each end: 1 .. * (one or more) 3 (exactly 3) (blank often means 1) A B Has-arelationships JButton JFrame BallButton JPanel BallWorldFrame BallWorld ButtonsPanel WorldPanel Ball World HotSpot We also use color (here, lime green, but more often I use red) to indicate has-a relationships that involve object creation. This is not standard UML.

  12. A B Has-arelationships JButton BallButton 1..* JFrame ButtonsPanel JPanel BallWorldFrame Notation: A has-a B, here, A creates a B Indicate the multiplicity on each end: 1 .. * (one or more), blank for exactly 1 BallWorlds WorldPanel 1..* Ball HotSpot World I chose to have the BallWorlds create each World, which creates the two panels (WorldPanel and ButtonPanel). Why? Who else might I have chosen to create the World? The Panels? At this point, we need to ask ourselves – what remains to be created? Who should create them? Part of an answer: I envision a single frame, but possibly many Worlds and associated Panels. Do you see why that leads to my choices?

  13. A B Has-arelationships JButton BallButton 1..* JFrame ButtonsPanel JPanel BallWorldFrame Notation: A has-a B, here, A creates a B Indicate the multiplicity on each end: 1 .. * (one or more), blank for exactly 1 BallWorld WorldPanel 1..* Ball HotSpot World 0..* We have yet to create the Balls and HotSpots? Who should create the HotSpots? Who creates a new Ball, e.g., a new Exploder? How? Answer: the World seems a natural choice. Answer: the human user, by pressing a BallButton.

  14. A B Has-arelationships JButton BallButton 1..* JFrame ButtonsPanel JPanel BallWorldFrame Notation: A has-a B, here, A creates a B Indicate the multiplicity on each end: 1 .. * (one or more), blank for exactly 1 BallWorld WorldPanel 1..* Ball HotSpot World 0..* So the human user creates each Ball (e.g. an Exploder), by pressing a BallButton. When the human presses a BallButton, a Ball of the appropriate type must be: Constructed Added to the World Drawn In the current design, the latter two are impossible. Explain.

  15. A B Has-arelationships JButton BallButton 1..* JFrame ButtonsPanel JPanel BallWorldFrame Notation: A has-a B, here, A creates a B Indicate the multiplicity on each end: 1 .. * (one or more), blank for exactly 1 BallWorld WorldPanel 1..* Ball HotSpot World 0..* So the human user creates each Ball (e.g. an Exploder), by pressing a BallButton. When the human presses a BallButton, a Ball of the appropriate type must be: Constructed Added to the World Drawn In the current design, the latter two are impossible. Draw the has-a relationships that are needed – who needs to know whom? These are has-a relationships, but do NOT involve creation of objects. How are these relationships going to be implemented?

  16. is-a JButton Relationships has-a BallButton 1..* ButtonsPanel JFrame 1..* JPanel • When a new Ball is created, it must be: • Constructed • Added to the World • Drawn • Who should construct the Ball? Add it to the World? Draw it? BallWorldFrame 1..* WorldPanel BallWorld 1..* Draw links to enable the construct/add/draw actions. Revise your answers to the “who-should” questions as needed, as you design. World Ball Dud Bouncer Bloater Exploder . . .

  17. is-a JButton Relationships has-a BallButton 1..* ButtonsPanel JFrame 1..* JPanel Draw links to enable the construct/add/draw actions. Revise your answers to the “who-should” questions as needed, as you design. Here are my decisions, as I made them. BallWorldFrame 1..* WorldPanel BallWorld 1..* BallButton: construct the new Ball. No links needed. (Why?) World BallButton: tell the World to add the Ball. What does that imply is needed in the diagram? Ball Dud Bouncer Bloater Exploder . . .

  18. is-a JButton Relationships has-a BallButton 1..* ButtonsPanel JFrame 1..* JPanel • BallButton: tell the World to add the Ball. Hence: • BallButton must have the World • World must be able to add a Ball • What has-a relationships does that imply need to be added, for the BallButton to have the World? BallWorldFrame 1..* WorldPanel BallWorld 1..* World BallButton: construct the new Ball. No links needed. How does the BallButton obtain the World? Ball Answer: BallWorldFrame creates the World, then sends it to the ButtonsPanel, who sends it to each BallButton. Do you see why it was a good decision for BallWorldFrame to create the 3 big things? Dud Bouncer Bloater Exploder . . .

  19. is-a JButton Relationships has-a BallButton 1..* ButtonsPanel JFrame 1..* JPanel The World is intended to hold all of the balls. What has-a does that imply? Draw it. BallWorldFrame 1..* WorldPanel BallWorld 1..* World Who creates a new Ball, e.g., a new Exploder? How? Answer: the human user, by pressing a BallButton. 1..* Ball Dud Bouncer Bloater Exploder . . .

  20. is-a JButton Relationships has-a BallButton 1..* ButtonsPanel JFrame 1..* JPanel Drawable interface BallWorldFrame 1..* WorldPanel BallWorld WorldManagement interface 1..* Animatable interface World 1..* Ball What about interfaces? – This is a chance to give the design strategic consistency by defining up front how the interacting entities should talk! Dud Bouncer Bloater Exploder . . .

  21. More questions • Attributes: • What does a Ball have? • When the human user clicks a BallButton, should the World become aware of the constructed Ball? If so, how? • How is drawing done? • WorldPanel gives info to Ball, or Ball gives info to WorldPanel? • How do Balls “act”? What else should the human user be able to do to Balls? How is that accomplished? • Who should act independently (i.e., what threads should exist)? • What interfaces would be useful in the above? In particular, what should the following be able to do: • Ball HotSpot ManagerOfBalls ManagerOfHotSpots

  22. Design BallWorld, by drawing a UML class diagram for it We just did our first iteration of Step 1 & 2 Review the specification, then: • Identify kinds of objects – these become classes • Identify relationships between classes • is-a (extends), is-a (implements), has-a • Identify interfaces that specify what is needed for the classes to relate • For each class, determine its attributes and operations • For each class, for each attribute/operation, determine its type Now we’ll continue with our first iteration of Step 3 & 4 We frequently retrace our steps and fine tune our design.

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