CS 245 Lecture 5 – Inheritance
Agenda
- what ?s
- program this
- the kinds of inheritance
- a ToasterPlus
- RandomPlus
- a raffle
TODO
- Read chapter 5 through section 5.2, Object: The Cosmic Superclass.
- 1/4 sheet with two questions and two observations.
Program This
Assume you have a Planet class:
public class Planet {
private String name;
private double ausFromTheSun;
private double relativeMass;
public Planet(String name,
double ausFromTheSun,
double relativeMass) {
this.name = name;
this.ausFromTheSun = ausFromTheSun;
this.relativeMass = relativeMass;
}
public String toString() {
return String.format("%15s %6.2f %6.2f", name, ausFromTheSun, relativeMass);
}
}
What changes do you need to make in order for Planet to be Comparable? In particular, a planet should be considered greater than another if it has a larger relative mass.
public interface Comparable<T> {
// Returns
// negative if this < other,
// 0 if this equals other, and
// positive if this > other.
public int compareTo(T other);
}
Once Planet is Comparable, some high-level conductor code in Arrays.sort can automatically sort an array for us.
Inheritance
With interfaces, we get interface inheritance, in which:
- subtypes look like their supertypes, allowing old call to call new code
Through extension, we get implementation inheritance, in which
- subtypes look like their supertypes, allowing old call to call new code
- subtypes inherit supertype methods, allow new code to reuse old code
Code
Planet.java
package lecture05;
public class Planet implements Comparable<Planet> {
private String name;
private double ausFromTheSun;
private double relativeMass;
public Planet(String name,
double ausFromTheSun,
double relativeMass) {
this.name = name;
this.ausFromTheSun = ausFromTheSun;
this.relativeMass = relativeMass;
}
public String toString() {
return String.format("%15s %6.2f %6.2f", name, ausFromTheSun, relativeMass);
}
public int compareTo(Planet other) {
if (Math.abs(relativeMass - other.relativeMass) < 0.001) {
return 0;
} else if (relativeMass < other.relativeMass) {
return -1;
} else {
return 1;
}
}
}
PlanetSorter.java
package lecture05;
import java.util.Arrays;
public class PlanetSorter {
public static void main(String[] args) {
Comparable[] planets = {
new Planet("Saturn", 9.5, 95.0),
new Planet("Earth", 1.0, 1.0),
new Planet("Venus", 0.7, 0.815),
new Planet("Jupiter", 5.2, 318.0),
new Planet("Uranus", 19.6, 14.0),
new Planet("Neptune", 30.0, 17.0),
new Planet("Mars", 1.5, 0.107),
new Planet("Mercury", 0.4, 0.055),
// "obtuse"
};
Arrays.sort(planets);
for (Comparable p : planets) {
System.out.println(p);
}
}
}
Bread.java
package lecture05;
public class Bread {
}
Toast.java
package lecture05;
public class Toast {
public int getCalories() {
return 100 * 2;
}
}
Toaster.java
package lecture05;
public class Toaster {
public Toast toast(Bread bread) {
return new Toast();
}
}
Dad.java
package lecture05;
public class Dad {
private int hitPoints;
public Dad() {
hitPoints = 100;
}
public void eatBreakfast(Toaster toaster) {
Toast toast = toaster.toast(new Bread());
hitPoints += toast.getCalories();
ToasterPlus toasterPlus = (ToasterPlus) toaster;
System.out.println(toasterPlus.getTime());
}
public int getHitPoints() {
return hitPoints;
}
}
ToasterPlus.java
package lecture05;
import java.awt.Toolkit;
import java.util.Date;
public class ToasterPlus extends Toaster {
public Date getTime() {
return new Date();
}
// We don't need this here, because we are extending Toaster.
public Toast toast(Bread bread) {
Toast toast = super.toast(bread);
for (int i = 0; i < 100; ++i) {
Toolkit.getDefaultToolkit().beep();
try {
Thread.sleep(100);
} catch (InterruptedException e) {
}
}
return toast;
}
}
Story.java
package lecture05;
public class Story {
public static void main(String[] args) {
Dad lowell = new Dad();
Toaster toaster = new ToasterPlus();
System.out.println(lowell.getHitPoints());
lowell.eatBreakfast(toaster);
System.out.println(lowell.getHitPoints());
}
}
RandomPlus.java
package lecture05;
import java.util.Random;
public class RandomPlus extends Random {
public int nextIntInRange(int lo, int hi) {
return lo + nextInt(hi - lo);
}
public static void main(String[] args) {
RandomPlus g = new RandomPlus();
for (int i = 0; i < 1000; ++i) {
System.out.println(g.nextIntInRange(1, 4));
}
}
}
Raffle.java
package lecture05;
import java.util.ArrayList;
import java.util.Random;
public class Raffle extends ArrayList<String> {
@Override
public boolean add(String name) {
if (name.equals("Jill")) {
// whoops
} else {
super.add(name);
}
return true;
}
public String drawName() {
Random g = new Random();
int i = g.nextInt(size());
return this.remove(i);
}
public static void main(String[] args) {
Raffle raffle = new Raffle();
raffle.add("Jill");
raffle.add("Alex G");
raffle.add("Nick L");
raffle.add("Jeff J");
raffle.add("Andrew P");
raffle.add("Nick D");
raffle.add("Jeremy R");
raffle.add("Trent S");
raffle.add("Robert F");
System.out.println(raffle.drawName());
System.out.println(raffle.drawName());
System.out.println(raffle.drawName());
System.out.println(raffle.drawName());
System.out.println(raffle.drawName());
}
}
MyFrame.java
package lecture05;
import javax.swing.JButton;
import javax.swing.JFrame;
public class MyFrame extends JFrame {
public MyFrame() {
super("my title");
// super();
JButton button = new JButton("Exit");
add(button);
// button.addActionListener();
setSize(1024, 512);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
}
public static void main(String[] args) {
MyFrame myFrame = new MyFrame();
}
}
Haiku
Dad: Where’s my Camry?
Jill: Out back. I “serviced” it.
Dad: The space shuttle!?
Jill: Out back. I “serviced” it.
Dad: The space shuttle!?