ChengJade1Part2.java

/**
 * This is a class implements a Java application that:
 *
 *   Executes 4 methods, 2 iterative and 2 recursive.
 *
 *   Accepts an integer Q on the command line. This integer is the input for
 *   all 4 methods.
 *
 *   If the command line has anything other than a single integer, the
 *   program prints an error message and exit.
 *
 *   If the integer Q is negative or zero, the program exits without printing
 *   anything.
 *
 *   Otherwise, executes each of the following four methods:
 *     Method 1: use a loop to print a row of Q asterisks.
 *     Method 2: use recursion to print a row of Q asterisks.
 *     Method 3: use a loop to print the numbers Q, Q - 1, ... 3, 2, 1.
 *     Method 4: use recursion to print the numbers Q, Q - 1, ... 3, 2, 1.
 *
 * @author     Jade Cheng
 * @assignment TA 2 part 2
 * @date       Jan 14, 2010
 * @bugs       None
 */
public class ChengJade1Part2 {
    /**
     * The entry point of the application.
     *
     * @param args The command line arguments.
     */
    public static void main(final String[] args) {

        // If the command line has anything other than a single integer, the
        // program prints an error message and exits.
        if (args.length != 1) {
            System.err.println("Wrong number of arguments.");
            System.exit(1);
        }
        int q = 0;
        try {
            q = Integer.parseInt(args[0]);
        } catch (final NumberFormatException e) {
            System.err.println("Argument is not an integer.");
            System.exit(1);
        }

        // If the integer Q is negative or zero, the program exits without
        // printing anything.
        if (q <= 0)
            System.exit(1);

        // Call the methods.
        ChengJade1Part2.printAsterisksWithLoop(q);
        System.out.println();
        ChengJade1Part2.printAsterisksRecursively(q);
        System.out.println();
        ChengJade1Part2.printNumbersWithLoop(q);
        System.out.println();
        ChengJade1Part2.printNumbersRecursively(q);

        // Exit cleanly while debugging from Eclipse.
        System.exit(0);
    }


    /**
     * Use recursion to print a row of Q asterisks.
     *
     * @param n The number of asterisks to print.
     */
    private static void printAsterisksRecursively(final int n) {
        assert n >= 0;
        if(n == 0)
            return;
        System.out.print("* ");
        printAsterisksRecursively(n-1);
    }


    /**
     * Use a loop to print a row of Q asterisks.
     *
     * @param n The number of asterisks to print.
     */
    private static void printAsterisksWithLoop(final int n) {
        assert n > 0;
        for (int i = 0; i < n - 1; i++)
            System.out.print("* ");
        System.out.print("*");
    }


    /**
     * Use recursion to print the numbers Q, Q - 1, ... 3, 2, 1.
     *
     * @param n The number of numbers to print.
     */
    private static void printNumbersRecursively(final int n) {
        assert n >= 0;
        if (n == 0)
            return;
        System.out.print(n + " ");
        ChengJade1Part2.printNumbersRecursively(n - 1);
    }


    /**
     * Use a loop to print the numbers Q, Q - 1, ... 3, 2, 1.
     *
     * @param n The number of numbers to print.
     */
    private static void printNumbersWithLoop(final int n) {
        assert n > 0;
        for (int i = n; i > 1; i--)
            System.out.print(i + " ");
        System.out.print(1);
    }
}