CSCI A201/A597 and I210
Lab Notes Twelve

Second semester 2000-2001

Sorting, inheritance, applets.

These lab notes contain the code we may be writing Thursday in class.

First the Selection Sort that we developed on Tuesday.

class One {
    static void sort(int[] a) {
	for (int i = 0; i < a.length - 1; i++) {
	    for (int j = i; j < a.length; j++) {
		if (a[i] > a[j]) { // sorting in ascending order
		    int temp = a[i]; 
		    a[i] = a[j]; 
		    a[j] = temp; 
		}
	    } 
	} 
    } 
    public static void main(String[] args) {
	int[] numbers = new int[args.length]; 
	for (int i = 0; i < numbers.length; i++) {
	    numbers[i] = Integer.parseInt(args[i]); 
	} 
	System.out.println("Here's the initial array: "); 
	One.show(numbers); 
	System.out.println("Let me sort it in ascending order..."); 
	One.sort(numbers);
	System.out.println("... Done\nHere it is sorted: "); 
	One.show(numbers); 

    } 
    static void show(int[] a) {
	for (int i = 0; i < a.length; i++) {
	    System.out.print(a[i] + " "); 
	} 
	System.out.println(); 
    } 
}

Here's how it runs:

frilled.cs.indiana.edu%javac One.java
frilled.cs.indiana.edu%java One 3 4 1 2 6 7
Here's the initial array: 
3 4 1 2 6 7 
Let me sort it in ascending order...
... Done
Here it is sorted: 
1 2 3 4 6 7 
frilled.cs.indiana.edu%

To clarify the idea of scope of a variable let's look at this example:

class Two {
    public static void main(String[] args) {
	int a = 1; 

	{ 
	    int b = 2;

	    System.out.println("a: " + a);
	    a = 4; // change will be seen by the other block
	    System.out.println("b: " + b);

	} 

	// System.out.println("b: " + b); 

	{ 
	    int b = 3;

	    System.out.println("a: " + a);
	    System.out.println("b: " + b);

	} 

    } 
}

I'll let you experiment with it.

Here's a second method of sorting: Bubble Sort.

class Three {
    static void sort(int[] a) {
	boolean done; 
	do { 
            done = true;
	    for (int i = 0; i < a.length - 1; i++) {
		if (a[i] > a[i + 1]) { // sort in ascending order 

		    int temp = a[i];
		    a[i] = a[i + 1];
		    a[i + 1] = temp;
		    done = false; 

		}
	    }
	} while (! done); 
    } 
    static void main(String[] args) {
	int[] numbers = new int[args.length]; 
	for (int i = 0; i < numbers.length; i++) {
	    numbers[i] = Integer.parseInt(args[i]); 
	} 
	System.out.println("Here's the initial array: "); 
	Three.show(numbers); 
	System.out.println("Let me sort it in ascending order..."); 
	Three.sort(numbers);
	System.out.println("... Done\nHere it is sorted: "); 
	Three.show(numbers); 

    } 
    static void show(int[] a) {
	for (int i = 0; i < a.length; i++) {
	    System.out.print(a[i] + " "); 
	} 
	System.out.println(); 
    } 
}

It runs just like the other one, but the mechanism is different.

The outer do-while loop is normally added at the end.

For this reason I find the following method much more intuitive.

class Four { 

    static void sort(int[] a) {
	boolean done = true; 
	for (int i = 0; i < a.length - 1; i++) {
	    if (a[i] > a[i + 1]) { // sort in ascending order 
		int temp = a[i];
		a[i] = a[i + 1];
		a[i + 1] = temp;
		done = false;
	    }
	}
	if (! done) 
	    sort(a);
    } 

    static void main(String[] args) {
	int[] numbers = new int[args.length]; 
	for (int i = 0; i < numbers.length; i++) {
	    numbers[i] = Integer.parseInt(args[i]); 
	} 
	System.out.println("Here's the initial array: "); 
	One.show(numbers); 
	System.out.println("Let me sort it in ascending order..."); 
	One.sort(numbers);
	System.out.println("... Done\nHere it is sorted: "); 
	One.show(numbers); 

    } 
    static void show(int[] a) {
	for (int i = 0; i < a.length; i++) {
	    System.out.print(a[i] + " "); 
	} 
	System.out.println(); 
    } 
}

Yes, recursion, in some cases, amounts to just a loop.

Can you draw a picture of this, like we did in class of Tuesday?

One could improve on the Bubble Sort technique above.

Here's an applet that illustrates the differences between three sorting methods:

quick sort (not selection sort)
regular bubble sort
improved bubble sorting

The applet, I believe, is very exciting.

It shows how the methods work, and illustrates topics from chapter 15.

Let's move on.

We will talk about inheritance.

The basic part we need to know is this example:

class Horse {
    void fun() {
	System.out.println("I am a Horse."); 
    } 
} 

class Unicorn extends Horse {
    void fun() {
	System.out.println("I am a Unicorn. Like a horse, but with a horn."); 
    }
}

class Experiment {
    public static void main(String[] args) {
	Horse      a = new Horse();
	Horse      b = new Unicorn(); 
	Unicorn    c = new Unicorn(); 
	// Unicorn d = new Horse(); 
	System.out.print("First test:  "); 
	a.fun(); // a horse, of course 
	System.out.print("Second test: "); 
	c.fun(); // a unicorn, of course
	System.out.print("Third test:  "); 
	b.fun(); // what will this be? 

    } 
}

Here's a picture to get the idea:

That's what you need to know to understand applets.

Now we have the following examples, for you to practice with them:

1. A Simple Applet

Create a file One.html with the following contents.

<HTML>
<HEAD>
<TITLE>Applet One</TITLE>
</HEAD>
<BODY>
<P>Here is my <U>first applet</U>.</P> 

<APPLET CODE="One.class" WIDTH=300 HEIGHT=300>

</APPLET> 

<P> Its title is <I>"Picasso in disbelief"</I>.</P> 


</BODY>
</HTML>

Create a file One.java with the following contents.

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

public class One extends Applet {
    public void paint (Graphics g) {
	Graphics2D g2 = (Graphics2D)g; 
	Rectangle a = new Rectangle(5, 10, 20, 30); 
	g2.draw(a); 
	a.translate(15, 25); 
	g2.draw(a); 
    }
}

Compile One.java and look at One.html with either Netscape or an appletviewer.

2. Graphical Shapes

Create a file Two.html with the following contents.

<HTML>
<HEAD>
<TITLE>Applet Two</TITLE>
</HEAD>
<BODY>
<P>Here is my <U>second applet</U>.</P> 

<APPLET CODE="Two.class" WIDTH=300 HEIGHT=300>

</APPLET> 

<P> Its title is <I>"Graphical Shapes"</I>.</P> 


</BODY>
</HTML>

Create a file Two.java with the following contents.

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

public class Two extends Applet {
    public void paint (Graphics g) {
	Graphics2D g2 = (Graphics2D)g; 

	Ellipse2D.Double m = new Ellipse2D.Double(5, 10, 150, 80); 
	g2.draw(m); // an ellipse 

        int x = 90; 
	int y = 90;
	int diam = 70; 
	Ellipse2D.Double q = new Ellipse2D.Double(x, y, diam, diam); 
	g2.draw(q); // a circle 

        Line2D.Double segment = new Line2D.Double(15, 150, 55, 90); 
	g2.draw(segment); // a line

        Point2D.Double start = new Point2D.Double(20, 155); 
        Point2D.Double stop = new Point2D.Double(60, 95); 
        segment = new Line2D.Double(start, stop); 
        g2.draw(segment); // another line

    }
}

Compile Two.java and look at Two.html with either Netscape or an appletviewer.

3. Color and Shapes

Create a file Three.html with the following contents.

<HTML>
<HEAD>
<TITLE>Applet Three</TITLE>
</HEAD>
<BODY>
<P>Here is my <U>third applet</U>.</P> 

<APPLET CODE="Three.class" WIDTH=300 HEIGHT=300>

</APPLET> 

<P> Its title is <I>"Colored Graphical Shapes"</I>.</P> 


</BODY>
</HTML>

Create a file Three.java with the following contents.

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

public class Three extends Applet {
    public void paint (Graphics g) {
	Graphics2D g2 = (Graphics2D)g; 

	Color magenta = new Color(1.0F, 0.0F, 1.0F); 
	g2.setColor(magenta); 
	Ellipse2D.Double m = new Ellipse2D.Double(5, 10, 150, 80); 
	g2.draw(m); // an ellipse 
	g2.fill(m); // fill it with the current color
	// magenta is still current color here 
        int x = 90; 
	int y = 90;
	int diam = 70; 
	g2.setColor(Color.red); // predefined color 
	Ellipse2D.Double q = new Ellipse2D.Double(x, y, diam, diam); 
	g2.draw(q); // a circle 
	g2.fill(q); // fill it with the current color
	g2.setColor(Color.blue); // another predefined color 
        Line2D.Double segment = new Line2D.Double(15, 150, 55, 90); 
	g2.draw(segment); // a line

        Point2D.Double start = new Point2D.Double(20, 155); 
        Point2D.Double stop = new Point2D.Double(60, 95); 
        segment = new Line2D.Double(start, stop); 
        g2.draw(segment); // another line
        // current color is blue here 
    }
}

Compile Three.java and look at Three.html with either Netscape or an appletviewer.

4. Text in Applets

Create a file Four.html with the following contents.

<HTML>
<HEAD>
<TITLE>Applet Four</TITLE>
</HEAD>
<BODY>
<P>Here is my <U>fourth applet</U>.</P> 

<APPLET CODE="Four.class" WIDTH=300 HEIGHT=300>

</APPLET> 

<P> Its title is <I>"Applet Applet"</I>.</P> 


</BODY>
</HTML>

Create a file Four.java with the following contents.

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

public class Four extends Applet {
    public void paint (Graphics g) {
	Graphics2D g2 = (Graphics2D)g; 

	g2.drawString("Applet", 50, 160); 

	final int HUGE_SIZE = 36; // fotn point size 
	String message = "Applet"; // actual text 
        // create Font object then call setFont on it 
	Font hugeFont = new Font("Serif",    // font face name 
				 Font.BOLD,  // style 
				 HUGE_SIZE); // point size   
        g2.setFont(hugeFont); // now g2 will write that way 
	g2.setColor(Color.green); // set color to predefined green 
	g2.drawString(message, 50, 100); // then write string 
    }
}

Compile Four.java and look at Four.html with either Netscape or an appletviewer.

5. Simple Drawing

Create a file Five.html with the following contents.

<HTML>
<HEAD>
<TITLE>Applet Five</TITLE>
</HEAD>
<BODY>
<P>Here is my <U>fourth applet</U>.</P> 

<APPLET CODE="Five.class" WIDTH=300 HEIGHT=300>

</APPLET> 

<P> Its title is <I>"Happy Hour"</I>.</P> 

</BODY>
</HTML>

Create a file Five.java with the following contents.

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

public class Five extends Applet {
    public void paint (Graphics g) {
	Graphics2D g2 = (Graphics2D)g; 

	Ellipse2D.Double e1 = new Ellipse2D.Double( 75, 40, 30, 70); 
	Ellipse2D.Double e2 = new Ellipse2D.Double(115, 40, 30, 70); 
	Ellipse2D.Double c1 = new Ellipse2D.Double( 85, 85, 15, 15); 
	Ellipse2D.Double c2 = new Ellipse2D.Double(125, 85, 15, 15); 
	Ellipse2D.Double n = new Ellipse2D.Double(55, 120, 110, 25); 

	Arc2D.Double m = 
           new Arc2D.Double(-40, -120, 300, 300, 230, 80, Arc2D.OPEN); 

	g2.draw(e1); 
	g2.draw(e2); 
	g2.fill(c1);
 	g2.fill(c2); 

	g2.draw(n); 

	g2.draw(m); 

    }
}

Compile Five.java and look at Five.html with either Netscape or an appletviewer.

Lab assignment: Take a look at the pictures below. Choose one that you like. Write an applet that draws that picture. Then turn the code in on Tuesday with the minute paper, in class.

Last updated: Apr 5, 2001 by Adrian German for A201

CSCI A201/A597 and I210 Lab Notes Twelve

CSCI A201/A597 and I210
Lab Notes Twelve