PopulationTable.java

import javax.swing.*;

/**
 * A table of historical population data.
 *
 * @author Jim Glenn
 * @version 0.1 11/20/2003
 */

public class PopulationTable
{
    private int[][] pop;

    private int numPlaces;

    /**
     * Creates a population table with all entries initialized to zero.
     * 
     * @param maxPlaces the maximum number of places that the new table can
     * hold information for
     * @param years the number of years' worth of data to keep for each place
     */

    public PopulationTable(int maxPlaces, int years)
    {
	pop = new int[maxPlaces][years];
	numPlaces = 0;

	/*
	 
	1) envision what it would look like w/o loops

	pop[0][0] = 0;
	pop[1][0] = 0;
        ...
	pop[maxPlaces - 1][0] = 0;
	pop[0][1] = 0;
	pop[1][1] = 0;
        ...
	pop[maxPlaces - 1][1] = 0;
	...
	pop[0][years - 1] = 0;
        ...
	pop[maxPlaces - 1][years - 1] = 0;


	2) find statements that can be replaced with loops

	for (int pl = 0; pl < maxPlaces; pl++)
	    pop[pl][0] = 0;

	for (int pl = 0; pl < maxPlaces; pl++)
	    pop[pl][1] = 0;

	...

	for (int pl = 0; pl < maxPlaces; pl++)
	    pop[pl][years - 1] = 0;

	3) combine loops

	for (int pl = 0; pl < maxPlaces; pl++)
	    {
		pop[pl][0] = 0;
		pop[p1][1] = 0;
                ...
		pop[pl][years - 1] = 0;
	    }

	4) look again for statements that can be replaced with loops
	*/

	for (int pl = 0; pl < maxPlaces; pl++)
	    for (int yr = 0; yr < years; yr++)
		pop[pl][yr] = 0;
    }

    /**
     * Adds one place to this table.
     *
     * @param p an array holding population counts for the new place;
     * the size of the array must match the number of years specified when
     * this table was created
     */

    public void addPlace(int[] p)
    {
	for (int yr = 0; yr < p.length; yr++)
	    pop[numPlaces][yr] = p[yr];
	
	numPlaces++;
    }

    /**
     * Returns the maximum value in this table.
     *
     * @return the maximum value in this table
     */

    public int findMax()
    {
	int max = Integer.MIN_VALUE;

	for (int pl = 0; pl < numPlaces; pl++)
	    for (int yr = 0; yr < pop[pl].length; yr++)
		max = Math.max(max, pop[pl][yr]);

	return max;
    }

    /**
     * Returns an array containing the percent changes for the specified place.
     *
     * @param pl the index of a place in this table
     * @return an array containing the percent changes for that place
     */

    public double[] getPercentChanges(int pl)
    {
	double[] pct = new double[pop[pl].length - 1];

	for (int yr = 0; yr < pct.length; yr++)
	    pct[yr] = 100 * (double)(pop[pl][yr] - pop[pl][yr + 1]) / pop[pl][yr + 1];
	return pct;
    }

    /**
     * Returns a string representation of this table.
     *
     * @return a string representation of this table
     */

    public String toString()
    {
	String s = "";

	for (int pl = 0; pl < numPlaces; pl++)
	    {
		for (int yr = 0; yr < pop[0].length; yr++)
		    s = s + pop[pl][yr] + '\t';
		s = s + '\n';
	    }

	return s;
    }

    /**
     * Calculates the total population for a given year.
     *
     * @param yr the year to calculate the total for
     * @return the population for that year
     */

    public int calcTotal(int yr)
    {
	int tot = 0;

	for (int pl = 0; pl < numPlaces; pl++)
	    tot += pop[pl][yr];

	return tot;
    }

    /**
     * Test driver for population table.
     *
     * @param args ignored
     */

    public static void main(String[] args)
    {
        // Data from US Census Bureau
	// there is a link to it here:
        // Index of Interesting Tables

	int[] alleganyPop = {74946, 80548, 84044, 84169};
	int[] aaPop = {427239, 370775, 297539, 206634};
	int[] countyPop = {692134, 655615, 621077, 492428};
	int[] calvertPop = {51372, 34638, 20863, 15826};
	int[] howardPop = {187328, 118572, 61911, 36152};
	int[] cityPop = {736014, 786775, 905759, 939024};

	PopulationTable mdTable = new PopulationTable(6, 4);

	mdTable.addPlace(alleganyPop);
	mdTable.addPlace(aaPop);
	mdTable.addPlace(countyPop);
	mdTable.addPlace(calvertPop);
	mdTable.addPlace(howardPop);
	mdTable.addPlace(cityPop);

	System.out.println(mdTable);
	
	System.out.println(mdTable.calcTotal(0));
	System.out.println(mdTable.findMax());

	double[] changes = mdTable.getPercentChanges(5);
	for (int i = 0; i < changes.length; i++)
	    System.out.print(changes[i] + "\t");
	System.out.println();
    }
}

This code can also be downloaded from the file PopulationTable.java.