teaching machines

CS 145 Lecture 22 – Designing objects

December 2, 2011 by Chris Johnson. Filed under cs145, fall 2011, lectures.

Agenda

• writing a Stopwatch
• objects hide information
• managing a “dungeon” with objects
• writing a flashlight

Code

Stopwatch.java

package lecture;

public class Stopwatch {
  /** Time at which stopwatch is started */
  private long startTime;

  /** Time at which stopwatch is stopped */
  private long stopTime;

  /**
   * Starts stopwatch.
   */
  public void start() {
    startTime = System.currentTimeMillis();
  }

  /**
   * Stops stopwatch.
   */
  public void stop() {
    stopTime = System.currentTimeMillis();
  }

  /**
   * Gets the number of seconds elapsed between start and stop.
   * 
   * @return Number of elapsed seconds.
   */
  public double getElapsedSeconds() {
    double difference = (stopTime - startTime) / 1000.0;
    return difference;
  }
}

AlphabetBackward.java

package lecture;

import java.util.Scanner;

public class AlphabetBackward {
  public static void main(String[] args) {
    
    
    Scanner in = new Scanner(System.in);
    
    System.out.println("Hit enter when ready.");
    in.nextLine();
    
    System.out.println("Enter alphabet backward: ");
    
    Stopwatch timer = new Stopwatch();
    
    // start timing here
    timer.start();
    String line = in.nextLine();
    timer.stop();
    // stop timing here

    if (line.equals("zyxwvutsrqponmlkjihgfedcba")) {
      System.out.println("Woo! You took " + timer.getElapsedSeconds() + " seconds.");
    } else {
      System.out.println("You are more forward-thinking.");
    }
  }
}

TODO

• Work on HW3. HW4 will be released early next week.

Haiku