20 QuestionsAssignment Intro

James WeiProfessor PeckMarch 19, 2014

Slides by James Wei

Outline• A look at the game of 20Q• Classes of 20Q/Model-View design• Implementation• Reading a file• Building a tree• Playing the game• Adding to the tree• Saving a file

A look at 20Q• We want to create a simplified version of 20Q• Here are the features we implement:• Can play 20Q• Can create game trees from files• Can improve tree when computer loses• Can save improved game trees to files

• Sample playthrough

Classes of 20Q• The classes of 20Q:• GameMain – runs 20Q• IAnimalModel – defines the methods and

behaviors available to the model• AnimalGameModel – implements IAnimalModel• AnimalGameViewer – handles display logic• AnimalNode – represents a node on the tree• WebGameInfo – don’t worry about this one

Model-View Design• Code is split between model and view• You write the model• Know how to interact with the view• Nothing new here…

Model-View Design

Implementation -- Overview

• A few parts to this assignment:• Reading a file: initialize()• Building a tree: initialize()• Playing the game: newGame(), processYesNo()• Adding to the tree: addNewQuestion(),

addNewKnowledge()• Saving a file: write()

• Also consider while you’re coding—what instance variables do we need in the model?

Implementation -- Overview

• View methods you will need to use:• void update(String) – displays text in main pane• void showMessage(String) – displays text in

message pane• void showDialog(String) – displays a popup with

the given text• void getNewInfoLeaf() – tells view to ask for a

new tree leaf• void getDifferentiator() – tells view to ask for a

new question node

Implementation -- Overview

Implementation – File I/O• Reading a file• Need to start by building the 20Q tree from a file• Implement this method:

void initialize(Scanner)• initialize must do the following:

• Use the scanner to read the file line by line• Use each line to build one node of the tree (in preorder)• Strip the “#Q:” from each question before creating its

internal node• Call myView.setEnabled(true)• Call newGame() at the very end to start a game

Implementation – File I/O

Implementation – File I/O• Your life will be much easier if you write a recursive

helper method• Some pseudo-code to get you started:

private AnimalNode readHelper(Scanner s){String line = s.nextLine();if (line is leaf) {// create new leaf}// recursively create left (yes) subtree// recursively create right (no) subtree// create internal node from subtrees}

Implementation – File I/O• Writing a file• Need to be able to save trees to file• Implement this method:

void write(FileWriter)• write must do the following:• Write one line in the file for each node using the

FileWriter write() method• Write a preorder traversal• Prepend “#Q:” for each question (internal node)• Append “\n” to the end of each line to signify new line

Implementation -- Overview

• A few parts to this assignment:• Reading a file: initialize()• Building a tree: initialize()• Playing the game: newGame(), processYesNo()• Adding to the tree: processYesNo(),

addNewQuestion(), addNewKnowledge()• Saving a file: write()

Implementation – Playing 20Q• Playing the game• Begins when the player clicks “New Game”, or

when the player loads a file, both of which call the model method newGame()

• First implement this method:void newGame()

• newGame must do the following:• Set all instance variables to their initial state• Ask the first question

Implementation – Playing 20Q• Playing the game• As you ask questions, the user responds with YES or

NO by clicking a button in the view—those buttons call processYesNo(boolean)

• Next implement this method:void processYesNo(boolean)

• processYesNo must do the following:• Update the current position on the game tree according to the

user’s response• Ask the next question – remember this varies depending on if

we are at an internal or a leaf!• Display a WIN or LOSE message if game has ended• Few more things which we’ll discuss in the next part…

Implementation -- Overview

• A few parts to this assignment:• Reading a file: initialize()• Building a tree: initialize()• Playing the game: newGame(), processYesNo()• Adding to the tree: processYesNo(),

addNewQuestion(), addNewKnowledge()• Saving a file: write()

Implementation – Improving• Improving the tree• If the computer loses, it’s time to add to our tree!• Go back and add to this method:

void processYesNo(boolean)• processYesNo must also do the following:• Ask for the answer (what were you thinking of?)• Call getNewInfoLeaf() – this will tell the view to

popup a dialog box where the user can type a response

Implementation – Improving• Improving the tree• getNewInfoLeaf will call another model method• Implement this method:

void addNewQuestion(String)• addNewQuestion must do the following:• Display a list of all of the user’s answers up to that

point, e.g. “You answered YES to <QUESTION>, You answered NO to <QUESTION>, etc.”

• Create a new leaf node for the correct answer• Ask for a differentiator question• Call getDifferentiator()

Implementation – Improving• Improving the tree• addNewQuestion will call the final method• Implement this method:

void addNewKnowledge(String)• addNewKnowledge must do the following:• Create a new internal node for the differentiator• Set the differentiator’s YES answer to the existing,

incorrect answer that the computer guessed, and the differentiator’s NO answer to the new, correct answer

• Add the internal node to the game tree• Start a new game

Implementation – Improving• Example – here’s the tree before playing:

For reference ->

Implementation – Improving• Example – here’s the tree after playing:

For reference ->

Wrapping Up• So you slept through this whole thing and now you

just want to know what to do, eh?• My recommended course of action:• Implement file I/O, aka initialize() and write()• Test by opening a file and saving it • Implement newGame() and processYesNo(), leaving

out improving the tree for now• Play the game – try winning and losing• Implement addNewQuestion() and

addNewKnowledge()• Test it – open a file, play several times (win/lose),

improve the tree, play with new tree, save file

Good luck!

I didn’t have time to find a witty tree or 20Q related cartoon…