Notes for Fri July 17, 2009. 

Experiment 1: 

class Person {
  void talk() {
    System.out.println("Howdy.");
  } 
}

class One {
  public static void main(String[] args) {
    Person a = new Person(); 
    a.talk(); 
  } 
}

I am defining a model for a person. A person can talk, saying: Howdy. 

Experiment 2:

class Person {
  void talk() {
    System.out.println("Howdy.");
  } 
}

class One {
  public static void main(String[] args) {
    Person a = new Person(); 
    a.talk(); 
    Student b = new Student(); 
    b.talk(); 
  } 
}

class Student extends Person {
  
}

A student is everything a person is (and I can add to that, but I am not here). 

Experiment 3: 

class Person {
  void talk() {
    System.out.println("Howdy.");
  } 
}

class One {
  public static void main(String[] args) {
    Person a = new Person(); 
    a.talk(); 
    Student b = new Student(); 
    b.talk(); 
    System.out.println( b.add(3, 5) - 2 ); 
  } 
}

class Student extends Person {
  int add(int n, int m) {
    return n + m; 
  } 
}

The new feature is add. 

Experiment 4:

class Person {
  void talk() {
    System.out.println("Howdy.");
  } 
}

class Student extends Person {
  int add(int n, int m) {
    return n + m; 
  } 
}

class ExchangeStudent extends Student {
  void talk() {
    System.out.println("Bonjour"); 
  } 
}

class One {
  public static void main(String[] args) {
    Person a = new Person(); 
    a.talk(); 
    Student b = new Student(); 
    b.talk(); 
    System.out.println( b.add(3, 5) - 2 ); 
    ExchangeStudent c = new ExchangeStudent(); 
    c.talk(); 
  } 
}

We can have more than two stages. 

Experiment 5:

class Person {
  void talk() {
    System.out.println("Howdy.");
  } 
}

class Student extends Person {
  int add(int n, int m) {
    return n + m; 
  } 
  void talk() {
    System.out.println("Bonjour"); 
  } 
}

class One {
  public static void main(String[] args) {
    Person a = new Person(); 
    a.talk(); // this prints Howdy 
    Student b = new Student(); 
    b.talk(); // this prints Bonjour but why?...

    Person c = new Student(); // polymorphism 
    c.talk(); // prints Bonjour 
    // dynamic method lookup 
    // System.out.println(c.add(3, 1)); 

    // Student d = new Person(); // not allowed 
  } 
}

Experiment 6:

/* <applet code=One.class width=400 height=300>
   </applet>
 */

import java.applet.*;
import java.awt.*; 

public class One extends Applet {
  int i; 
  public void paint(Graphics g) {
    i += 1; 
    System.out.println("I am painting..." + i); 
  } 
} 

Experiment 7:

class Person {
  void talk() {
    System.out.println("Howdy.");
  } 
}

class Student extends Person {
  int add(int n, int m) {
    return n + m; 
  } 
  void talk() {
    super.talk(); 
    System.out.println("Bonjour"); 
  } 
}

class One {
  public static void main(String[] args) {
    Person c = new Student(); 
    c.talk();
  } 
}

Experiment 8: 

/* <applet code=One.class width=400 height=300>
   </applet>
 */

import java.applet.*;
import java.awt.*; 
import java.awt.event.*; 

public class One extends Applet {
  public void init() {
    Two referee = new Two(); 
    this.addMouseMotionListener(referee); 
  } 
  public void paint(Graphics g) {

  } 
}

class Two implements MouseMotionListener {
   public void mouseMoved(MouseEvent e) {
     System.out.println("Mouse moved at (" + e.getX() + ", " + e.getY() + ")"); 
   }
   public void mouseDragged(MouseEvent e) {
     System.out.println("Mouse dragged..."); 
   } 
}  

This further emphasized that in Java typically we override/provide only pieces of an otherwise much bigger mechanism. 

Experiment 9 (just with Nathan): 

/* <applet code=One.class width=400 height=300>
   </applet>
 */

import java.applet.*;
import java.awt.*; 

public class One extends Applet {
  public void paint(Graphics g) {
    g.drawString("I am here", 50, 50); 
  } 
}

Experiment 10 (also with Nathan): 

/* <applet code=One.class width=400 height=300>
   </applet>
 */

import java.applet.*;
import java.awt.*; 
import java.awt.event.*; 

public class One extends Applet {
  public void init() {
    Two referee = new Two(this); 
    this.addMouseMotionListener(referee); 
  } 
  public void paint(Graphics g) {

  } 
}

class Two implements MouseMotionListener {
   One applet; 
   int px, py; 
   Two(One applet) {
     this.applet = applet;
     px = -1;
     py = -1; 
   } 
   public void mouseMoved(MouseEvent e) {
     System.out.println("Mouse moved at (" + e.getX() + ", " + e.getY() + ")"); 
     this.px = -1;
     this.py = -1;
   }
   public void mouseDragged(MouseEvent e) {
     System.out.println("Mouse dragged..."); 
     Graphics g = this.applet.getGraphics(); 
     int x = e.getX(); 
     int y = e.getY(); 
     if (this.px < 0) { 
       
     } else { 
       g.drawLine(px, py, x, y); 
     } 
     this.px = x;
     this.py = y; 
   } 
}  

Over the weekend I am going to work on your assignments and will write to you individually.