Code-Bin #1236 - CS2504 Lab 4

CS2504 Lab 4
Posted by: Sean Kelleher | April 23, 2011 @ 9:45am

Revision 1 - Original post on April 23, 2011 @ 9:43am

Java Code

/**
 * Captures the idea of the ballot paper completed by one voter.
 */
public class BallotPaper {

/**
     * Holds the preferences of this voter.
     */
    private Map<Integer, Candidate> preferences;

/**
     * Keeps track of the highest preference
     */
    private int highestPreference;

/**
     * The default constructor, initialises the ballot paper.
     */
    public BallotPaper() {
        preferences = new ArrayBasedMap<Integer, Candidate>();
        highestPreference = 0;
    }

/**
     * Set the {@code preference}-th preference for candidate
     * {@code candidate}.
     */
    public void setPreference( int preference, Candidate candidate ) {
        if ( preference > 0 ) {
            highestPreference =
                Math.max( preference, highestPreference );
            preferences.put( preference, candidate );
        } else {
            System.out.println( "Illegal preference: You must give a"
                                + " preference of at least 1." );
        }
    }

/**
     * Gets the candidate corresponding to a particular voter's
     * preference.
     */
    public Candidate getPreference( int preference ) {
        return preferences.get( preference );
    }

/**
     * Determines whether this ballot paper is valid.
     *
     * <p>A {@code BallotPaper} is valid if the highest preference is
     * equal to the number of candidates that have been voted for, and
     * the number of candidates that have been voted for are equal to
     * the number of candidates that are running.</p>
     */
    public boolean isValidBallot( int numCandidates ) {
        return (preferences.size() - 1) == highestPreference
            && (preferences.size() - 1) == numCandidates;
    }
}

/**
 * Records the details of an individual candidate (name and party).
 */
public class Candidate {

/**
     * The candidate's name.
     */
    private String name;

/**
     * The candidate's party.
     */
    private String party;

/**
     * The default constructor.
     */
    public Candidate() {
        name  = "";
        party = "";
    }

/**
     * Sets the value of {@code name}.
     *
     * @param name the new value of {@code name}.
     */
    public void setName( String name ) {
        this.name = name;
    }

/**
     * Returns the value of {@code name}.
     *
     * @return the value of {@code name}.
     */
    public String getName() {
        return name;
    }

/**
     * Sets the value of {@code party}.
     *
     * @param party the new value of {@code party}.
     */
    public void setParty( String party ) {
        this.party = party;
    }

/**
     * Returns the value of {@code party}.
     *
     * @return the value of {@code party}.
     */
    public String getParty() {
        return party;
    }
}

public class VoteCounter {

private Map<Candidate, List<BallotPaper>> votes;

private final int numCandidates;

public VoteCounter( List<Candidate> candidates ) {
        votes = ArrayBasedMap<Candidate, List<BallotPaper>>();

// Associate a list of ballot papers with each candidate
        for ( Candidate candidate : candidates ) {
            votes.put( candidate, new ArrayBasedList<BallotPaper>() );
        }

numCandidates = votes.size();
    }

/**
     * Determine the outcome of the election based on the votes in
     * {@code votesCast}.
     *
     * <p>Return the winning candidate.</p>
     *
     * @param votesCast the completed ballot papers.
     * @return the winning candidate.
     */
    public Candidate determineResult( List<BallotPaper> votesCast ) {
        int candidatesLeft = numCandidates;
        int lowestVotes;
        Candidate lowestScorer;

while ( candidatesLeft > 1 ) {
            for ( BallotPaper vote : votesCast ) {
                // Return candidate with currently highest preference
                final Candidate c = vote.get( candidatesLeft - 1 );
                final List<BallotPaper> vs  = votes.get( c );
                vs.add( vote );
            }
        }
    }
}

/**
 * A unit testing suite for the {@code VoteCounter} class.
 */
public class VoteCounterTest {

public static void main( String[] args ) {
        List<Candidate> candidates = new ArrayBasedList<Candidate>();

candidates.add( new Candidate() );
        candidates.get( 0 ).setName( "John" );
        candidates.get( 0 ).setParty( "FF" );

List<BallotPaper> votes = new ArrayBasedList<BallotPaper>();

votes.add( new BallotPaper() );
        votes.get( 0 ).setPreference( 1, candidates.get( 0 ) );

votes.add( new BallotPaper() );
        votes.get( 1 ).setPreference( 1, candidates.get( 0 ) );

VoteCounter counter = new VoteCounter( candidates );
        Candidate winner    = counter.determineResult( votes );
        System.out.println( winner.getName() );
    }
}

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