Recitation 7 Godfrey Tan March 21, 2002

Administrivia PS6 due Tuesday right after break Final Project descriptions will be handed out Monday after break Each group must agree on the common project If you are not satisfied with your group assignment, you should complain to me by the end of recitation.

Final Project Choice of two projects: Gizmoball, Anti-chess Equal difficulty/amount of work Each TA will provide help on one of two projects A “spec amendment” will be introduced halfway through your project

Gizmoball Ball bounced around by gizmos (demo) Physics package will be provided can be extended (e.g. magnetic field, relativity) Open-ended goal pin-ball, visual effect, physics simulation, etc. GUI/graphics intensive Competition?

Antichess Like Chess but the winning objective is to lose all your pieces Involves: chess board design, AI player, referee Algorithmically intensive Anti-chess tournament

Choosing Your Project Preliminary descriptions will be posted on April 1 People without a group should indicate their preference by this afternoon to help us assign groups will be sent to the class soon

True Subtyping Substitution priniciple Subtypes must be substitutable for supertypes The rep invariants and specification constraints of the supertypes must not be violated by the subtypes Subtypes may have more methods and properties so long as they abide by the substitution principle.

Subclassing in Java Pure implementation inheritance Does not worry about the behavioral constraints

Problems with subclassing Break encapsulation May lead to abuse: sub-classing things that are not subtypes (e.g. Stack extends Vector) Should only be used when a true sub- type relationship exists

Example class IHashSet extends HashSet { private int addCount; … public void add(Object o) { addCount++; super.add(o); } public void addAll(Collection c) { addCount += c.size(); super.addAll(c); }

Example class IHashSet extends HashSet { private int addCount; … addCount … public void add(Object o) { addCount++; super.add(o); }

Composition and Forwarding Composition: A class that contains another class (a wrapper) Forwarding: A class that calls methods of the other class that it contains No longer a subtype; rather, it is a different implementation of the same interface IHashSet extends Set vs IHashSet implements Set Gives programmer more control with method dispatching (vs Java’s default) Drawback: more code; less efficient (added level of indirection)

Example class IHashSet implements Set { private HashSet s; private int addCount; … public void add(Object o) { addCount++; s.add(o); } public void addAll(Collection c) { addCount += c.size(); s.addAll(c); }

pset 6 Design, implement GUI and then integrate it with your backend Testing GUI Use state machine to model GUI events Decouple GUI testing from backend testing Insert println statements before and after you call backend API method or, create a dumb backend “stub”

State Machine Directed graph: nodes represent a state and arcs represent a transition (action) caused by an input (event) Initial Portfolio Name Input Add Portfolio Button Pressed

Testing Excite all transitions with all boundary inputs (e.g., adding a Portfolio with new name, with an existing name, etc.) GUI should handle exceptional inputs (e.g. entering alphabets instead of numbers for number of stocks to purchase)

Integration Testing Repeat your GUI test (using the same input values from your backend tests if possible), and check if your program still works! Hopefully, you will have repChk() in your backend to catch your bugs.