ChengJade01Part2.java

import java.util.InputMismatchException;

/**
 * This is a class implements a Java application that:
 * <ul>
 * <li>executes 4 methods, 2 iterative and 2 recursive.</li>
 * <li>accepts an integer Q on the command line. This integer is the input for
 * all 4 methods.</li>
 * <li>if the command line has anything other than a single integer, the
 * program prints an error message and exit.</li>
 * <li>if the integer Q is negative or zero, the program exits without printing
 * anything.</li>
 * <li>otherwise, executes each of the following four methods:
 * <ol>
 * <li>Method 1: use a loop to print a row of Q asterisks.</li>
 * <li>Method 2: use recursion to print a row of Q asterisks.</li>
 * <li>Method 3: use a loop to print the numbers Q, Q - 1, ... 3, 2, 1.</li>
 * <li>Method 4: use recursion to print the numbers Q, Q - 1, ... 3, 2, 1.</li>
 * </ol>
 * </li>
 * </ul>
 * 
 * @author     Cheng Yu
 * @assignment TA 2 part 2
 * @date       Aug 29, 2008
 * @bugs       None
 */
public class ChengJade01Part2 {
  /**
   * 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.");
      return;
    }
    int q = 0;
    try {
      q = Integer.parseInt(args[0]);
    } catch (final NumberFormatException e) {
      System.err.print("Argument is not an integer.");
      return;
    }

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

    // Call the methods.
    ChengJade01Part2.printAsterisksWithLoop(q);
    System.out.println();
    ChengJade01Part2.printAsterisksRecursively(q);
    System.out.println();
    ChengJade01Part2.printNumbersWithLoop(q);
    System.out.println();
    ChengJade01Part2.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 == 1) {
      System.out.print("*");
      return;
    }
    System.out.print("* ");
    ChengJade01Part2.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 == 1) {
      System.out.print(1);
      return;
    }
    System.out.print(n + " ");
    ChengJade01Part2.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);
  }
}