» CS 245 Lecture 6 – Inheritance

CS 245 Lecture 6 – Inheritance

September 19, 2013 by Chris Johnson. Filed under cs245, fall 2013, lectures.

Agenda

reusing more than signatures
ToasterPlus
a Raffle
Drawer

TODO

Read chapter 5 in Core Java, through section 5.1. 1/4 sheet.

Inheritance

Interface inheritance: reuse method signatures so that generalized code can operate on our classes. This lets old code call new code.

Implementation inheritance: reuse method signatures and bodies so that we can extend existing classes. This lets new code build on old code. We also get interface inheritance.

Program This

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Code

Story.java

package lecture0919;

public class Story {
  public static void main(String[] args) {
    Dad dad = new Dad();
    dad.eatBreakfast(new ToasterPlus());
  }
}

Dad.java

package lecture0919;

public class Dad {
  private int hitPoints;

  public void eatBreakfast(Toaster toaster) {
    Toast toast = toaster.toast();
    hitPoints += toast.getCalorieCount();

    // toaster.getTime(); ILL EAGLE
  }
}

Toast.java

package lecture0919;

public class Toast {
  public int getCalorieCount() {
    return 155;
  }
}

Toaster.java

package lecture0919;

public class Toaster {

  public Toast toast() {
    try {
      Thread.sleep(3000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    
    return new Toast();
  }

}

ToasterPlus.java

package lecture0919;

import java.awt.Toolkit;
import java.io.IOException;
import java.util.Date;

public class ToasterPlus extends Toaster {

  public Toast toast() {

    // toast like normal
    Toast toast = super.toast();

    for (int i = 0; i < 10; ++i) {
      Toolkit.getDefaultToolkit().beep();
      System.out.println("\007");
      try {
        Process p = Runtime.getRuntime().exec("mplayer file:///usr/share/aisleriot/sounds/splat.ogg");
        p.waitFor();
      } catch (IOException e) {
      } catch (InterruptedException e) {
      }
    }
    
    System.out.println("Your toast was done at " + getTime());
    
    return toast;
  }

  public Date getTime() {
    return new Date();
  }
}

RandomWithRange.java

package lecture0919;

import java.util.Arrays;
import java.util.Random;

public class RandomWithRange extends Random {

  public int nextInt(int lower, int upper) {
    return nextInt(upper - lower + 1) + lower;
  }
  
  public static void main(String[] args) {
    RandomWithRange generator = new RandomWithRange();
    int[] counts = new int[3];
    
    for (int i = 0; i < 1000000000; ++i) {
      int r = generator.nextInt(-1, 1);
      ++counts[r + 1];
    }
    
    System.out.println(Arrays.toString(counts));
  }
}

WinnerWinnerChickenDinner.java

package lecture0919;

public class WinnerWinnerChickenDinner {
  public static void main(String[] args) {
    Raffle raffle = new Raffle();
    
    raffle.add("Jamison");
    raffle.add("Justin");
    raffle.add("Noah");
    raffle.add("Ben");
    raffle.add("Alan");
    raffle.add("Brad");
    raffle.add("Me");
    
    String winner = raffle.drawRandom();
    System.out.println(winner);
  }
}

Raffle.java

package lecture0919;

import java.util.ArrayList;
import java.util.Random;

public class Raffle extends ArrayList<String> {

  @Override
  public boolean add(String name) {
    if (!name.startsWith("Jill")) {
      super.add(name);
    }
    
    return true;
  }
  
  public String drawRandom() {
    
    Random generator = new Random();
    int randomIndex = generator.nextInt(size());
    
    String name = get(randomIndex);
    
    remove(randomIndex);
    
    return name;
  }
}

Haiku

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