A201/A597/I210 Introduction to Programming I (4/3 cr.)

Second Summer 2002

Lab Notes One: Getting Started.

Goals for the first lab:

Become familiar with your computer:
1. Login
2. Explore and understand files and folders
3. Locate Java compiler
4. Edit, compile and run your first Java program
5. Running Java from the DOS command prompt
Recognize syntax and logic errors
Work with classes and objects

Here are the steps for this lab:

Check that you appear in Postem (in A201-4285 even if you are taking I210 or A597.)
If something is wrong please e-mail dgerman@indiana.edu immediately.
Start Notepad (it should be under Utilities) and create a file.

The text of the file should be:

public class One {
  public static void main(String[] args) {
    System.out.println("Hello, world!"); 
  } 
}

Save this file as One.java on the desktop.
Open an MS-DOS command window.
Find the file that you have just created (use dir One.java or something similar). Note that you need to make sure you're accessing the folder that corresponds to the desktop.
Compile the file (use javac One.java)
Find the resulting class (dir One.class)
Run the program: (use java One)
Remember that these are the steps of program development:
1. Create (edit) a program in a file (extension .java)
2. Compile that .java file with javac (a .class gets created)
3. Run the program (the .class file) with java
Use your textbook. Sections 1.7, 1.8 are going to help you.

Now change the contents of One.java as follows:

public class One {
  public static void main(String[] args) {
    System.out.println("Hi, there!"); 
  } 
}

Note that the part that changed is in blue.

Save the file, compile and run One once again. What's the outcome?

Now change the file as follows:

public class One { public static void main(String[] 
args) { System.out.println("Hi,       there!"); } }

Notice we only change the amount of existing blank space, nothing else.

Save and compile the file, then run the program. What's the outcome?

Now change the file to:

public 
class 
One 
{
public 
static 
void 
main
(
String
[
] 
args
) 
{
System.out.println("Hi, there!"); 
} 
}

Save and compile the file, run the program. What's the outcome?
Does the book have anything to say about it (pp. 21-22, 23)?

Now change the program as follows:

public class One {
  public static void main(String[] args) {
    System.out.println("Hello, world!"); 
    System.out.println("Hello, again!"); 
  } 
}

Compile and run the program. What's the outcome?

Make a new change, and try this program:

public class One {
  public static void main(String[] args) {
    System.out.println("       again!"); 
    System.out.println("Hello,       "); 
  } 
}

Then try this one:

public class One {
  public static void main(String[] args) {
    System.out.println("    are     "); 
    System.out.println("How         "); 
    System.out.println("        you?"); 
  } 
}

Can you write a program that produces this output?
```
     4
    4
   4
  4   4
 44444444
      4
      4
```
It's a big "4" made out of little "4"'s. (See also exercise P1.2 in the book).

Try the following program and explain its output:

public class One {
  public static void main(String[] args) {
    System.out.println(1 + 2 + 3); 
  } 
}

Try the following program and explain its output:

public class One {
  public static void main(String[] args) {
    System.out.println(1 + 2 * 3); 
  } 
}

Is the next program different?

public class One {
  public static void main(String[] args) {
    System.out.println((1 + 2) * 3); 
  } 
}

Solve problem P1.3 (page 45) now.

Try this program:

public class One {
  public static void main(String[] args) {
    System.out.println("Hello, D'Artagnan!"); 
  } 
}

We can print single quotes quite easily.

Now put "D'Artagnan" in double quotes:

public class One {
  public static void main(String[] args) {
    System.out.println("Hello, "D'Artagnan"!"); 
  } 
}

Compile and run this program. What happens?

Try this:

public class One {
  public static void main(String[] args) {
    System.out.println("Hello, \"D'Artagnan\"!"); 
  } 
}

Explain the outcome.

Now try this program:

public class One {
  public static void main(String[] args) {
    System.out.println("Hello, \nworld!"); 
  } 
}

Explain what it does.

Recall the program that outputs this:
```
     4
    4
   4
  4   4
 44444444
      4
      4
```
Can you write that program with just one System.out.println?
Can you write a program that outputs a "4" made out of double quotes (")?
```
     "
    "
   "
  "   "
 """"""""
      "
      "
```

Try this program and explain the outcome:

public class One {
  public static void main(String[] args) {
    System.out.print("Hello, "); 
    System.out.print("world!"); 
  } 
}

What's the output of this program?

public class One {
  public static void main(String[] args) {
    System.out.print("A"); 
    System.out.print("B\n"); 
    System.out.print("C"); 
    System.out.print("D"); 
    System.out.print("E\n"); 
  } 
}

Read section 1.9 (pp. 27-29) now, carefully.

One final challenge. Can you write a program that produces this:

          .8.           8 888888888o          ,o888888o.
         .888.          8 8888    `88.       8888     `88.
        :88888.         8 8888     `88    ,8 8888       `8.
       . `88888.        8 8888     ,88    88 8888
      .8. `88888.       8 8888.   ,88'    88 8888
     .8`8. `88888.      8 8888888888      88 8888
    .8' `8. `88888.     8 8888    `88.    88 8888
   .8'   `8. `88888.    8 8888      88    `8 8888       .8'
  .888888888. `88888.   8 8888    ,88'       8888     ,88'
 .8'       `8. `88888.  8 888888888P          `8888888P'

You don't need to write this program, just think whether you can write it or not.

Also compile and run this program, as shown in lecture:

import java.awt.Color;
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingConstants;
import javax.swing.event.ChangeListener;
import javax.swing.event.ChangeEvent;

public class SliderTest
{
  public static void main(String[] args)
  {
    SliderFrame frame = new SliderFrame();
    frame.setTitle("SliderTest");
    frame.show();
  }
}

class SliderFrame extends JFrame
{
  public SliderFrame()
  {
    final int DEFAULT_FRAME_WIDTH = 300;
    final int DEFAULT_FRAME_HEIGHT = 300;
    setSize(DEFAULT_FRAME_WIDTH, DEFAULT_FRAME_HEIGHT);
    addWindowListener(new WindowCloser());
    colorPanel = new JPanel();
    ColorListener listener = new ColorListener();

    redSlider = new JSlider(0, 100, 100);
    redSlider.addChangeListener(listener);

    greenSlider = new JSlider(0, 100, 70);
    greenSlider.addChangeListener(listener);


    blueSlider = new JSlider(0, 100, 100);
    blueSlider.addChangeListener(listener);

    JPanel southPanel = new JPanel();
    southPanel.setLayout(new GridLayout(3, 2));
    southPanel.add(new JLabel("Red", SwingConstants.RIGHT));
    southPanel.add(redSlider);
    southPanel.add(new JLabel("Green", SwingConstants.RIGHT));
    southPanel.add(greenSlider);
    southPanel.add(new JLabel("Blue", SwingConstants.RIGHT));
    southPanel.add(blueSlider);

    Container contentPane = getContentPane();
    contentPane.add(colorPanel, "Center");
    contentPane.add(southPanel, "South");

    setSampleColor();
  }

  public void setSampleColor()
  {
    float red = 0.01F * redSlider.getValue();
    float green = 0.01F * greenSlider.getValue();
    float blue = 0.01F * blueSlider.getValue();

    colorPanel.setBackground(new Color(red, green, blue));
    colorPanel.repaint();
  }
  
  private JPanel colorPanel;
  private JSlider redSlider;
  private JSlider greenSlider;
  private JSlider blueSlider;
   
  private class ColorListener implements ChangeListener
  {
    public void stateChanged(ChangeEvent event)
    {
      setSampleColor();
    }
  }

  private class WindowCloser extends WindowAdapter
  {
    public void windowClosing(WindowEvent event) 
    {
        System.exit(0);
    }
  }
}

You don't need to understand this program, but you should have no problem creating, compiling, and running it. And when you see it running you should feel happy about it!

The goal for this semester's work is to understand thoroughly a program such as this.
(See http://www.cs.indiana.edu/classes/a201-dger/spr2001/labs/nine/alienU.html)

A second large program will be discussed, you can work with it here.
(See http://www.cs.indiana.edu/classes/a348/t540/lectures/iceblox/iceblox.html)

What comes next is:

A201/A597 LAB ASSIGNMENT ONE

There are two parts to this first lab assignment:

First, write a program that prints a staircase:

         +--+
         |  |
      +--+--+
      |  |  |
   +--+--+--+
   |  |  |  |
+--+--+--+--+
|  |  |  |  |
+--+--+--+--+

Show it to your AI next lab (Thursday).

Second, write a program as described below.

In your program:

Create a square room composed of 100 tiles (10 x 10, that is).
Create a Penguin, and add it to the room in the 8^th line and 3^rd column.
That means tile (7, 2) given our the numbering convention.
So, please take some time to review the numbering convention now.
Now ask the penguin to turn around and move to tile (2, 2).
Then ask the penguin to turn right, then move to tile (2, 7).
Then make the penguin turn right, and have it move to tile (7, 7).
Now ask the penguin to move to tile (2, 7).
And finally have it return to (7, 2), passing through (2, 2).

Show this program to your instructor in lab.

What you will need (essentially) two things:

The class Penguin.java (which you can find below):

import java.awt.*; 

class Penguin { 
    Rink location; 
    int speed = 100; 
    void placeIn(Rink placement, int x, int y) {
	this.location = placement; 
	frames = this.location.small; 
        this.x = x * 30; this.y = y * 30; 
	this.report(); 
    }
    int x, y, dx = 6, dy = 6, look = 2; 
    Image[] frames; 
    int animP[] = {    7,  8,  9,  8, //  left ( west)
		      10, 11, 12, 11, // right ( east) 
		       4,  5,  6,  5, //    up (north)
		       1,  2,  3,  2  //  down (south)
    }; 
    Penguin() {
	this.speed = 100; 
    }
    String direction = "south"; 
    void pause() { 
	try { 
	    Thread.sleep(speed * 10); 
	} catch (InterruptedException e) { } 
    }
    void think() { 
	try { 
	    Thread.sleep(100); 
	} catch (InterruptedException e) { } 
    }
    void report() { location.repaint(); } 
    void turnLeft() { 
	think(); 
	if (direction.equals("south")) { 
	    direction = "east"; 
	    look = 12; 
	} else if (direction.equals("east")) { 
	    direction = "north"; 
	    look = 5; 
	} else if (direction.equals("north")) { 
	    direction = "west"; 
	    look = 7; 
	} else { 
	    direction = "south"; 
	    look = 2; 
	}
	report(); 
    }
    void wave() {
	for (int i = 0; i <  4; i++) { 
	    think(); look =  0; report(); 
	    think(); look = 39; report(); 
	}
	think(); look =  0; report(); 
    }
    void happy() {
	think(); 
	if (direction.equals("south")) { 
	    wave(); think(); look = 2; report(); 
	} else if (direction.equals("east")) { 
	    look = 2; wave(); think(); look = 12; report();
	} else if (direction.equals("north")) { 
	    look =  7; report(); think(); 
	    look =  2; report(); wave(); think(); 
	    look =  7; report(); think(); 
	    look =  5; report(); think(); 
	} else { // west 
	    look = 2; report(); wave(); 
	    look = 7; report(); think(); 
	}
    }
    void turnRight() { 
	think(); 
	if (direction.equals("south")) { 
	    direction = "west"; 
	    look = 7; 
	} else if (direction.equals("east")) { 
	    direction = "south"; 
	    look = 2; 
	} else if (direction.equals("north")) { 
	    direction = "east"; 
	    look = 12; 
	} else { 
	    direction = "north"; 
	    look = 5; 
	}
	report(); 
    }
    void moveForward() {   
	for (int i = 0; i < 5; i++) { 
	    think(); 
	    if (direction.equals("south")) { 
		y += dy; 
		look = animP[12 + (i + 1) % 4]; 
	    } else if (direction.equals("east")) { 
		x += dx; 
		look = animP[ 4 + (i + 2) % 4]; 
	    } else if (direction.equals("north")) { 
		y -= dy; 
		look = animP[ 8 + (i + 1) % 4]; 
	    } else { // west 
		x -= dx; 
		look = animP[ 0 + i % 4]; 
	    }
	    report(); 
	}
    }
    void draw(Graphics g) {
	g.drawImage(frames[look], x, y, location); 
    }    
} // Penguin

Rink.java (which represents the theater where all this happens)

import java.net.*; 
import java.awt.*;
import javax.swing.*; 
import java.awt.event.*; 
import java.awt.image.*; 

class Rink extends JFrame {
    int cellWidth  = 30, 
	cellHeight = 30;  
    Penguin skater; 
    static Image small[]; 
    Rink(int columns, int rows) { 
	String pictureURL = "http://www.cs.indiana.edu/classes" + 
	    "/a348/CTED/moduleFour/lectures/iceblox/iceblox.gif"; 
	MediaTracker tracker = new MediaTracker(this); 
	Image collection; 
	try { 
	    collection = 
		Toolkit.getDefaultToolkit().getImage(new URL(pictureURL));
	} catch (Exception e) { 
	    collection = 
		Toolkit.getDefaultToolkit().getImage("iceblox.gif");
	}
	tracker.addImage(collection, 0); 
	try { tracker.waitForID(0); } catch (InterruptedException e) { } 
	ImageProducer collectionProducer = collection.getSource(); 
	int smalls = 48; 
	small = new Image[smalls]; 
	int k = 0, i = 0, j = 0; 
	ImageFilter filter; 
	while (k < smalls) {
	    filter = new CropImageFilter(j*30, i*30, 30, 30);   
	    small[k] = 
		createImage(new FilteredImageSource(collectionProducer, 
						    filter)); 
	    tracker.addImage(small[k], 1); 
	    k++; j++; if (j == 8) { j = 0; i++; } 
	}
	try { tracker.waitForID(1); } catch (InterruptedException e) { } 
	this.setSize(columns * cellWidth + cellWidth / 2, 
		     (1 + rows) * cellHeight + cellHeight / 2); 
	addWindowListener(new WindowCloser()); 
	getContentPane().add(new Surface(columns, rows), "Center"); 
	setTitle("Exercise for Lab One: The Wrong Trousers"); 
	this.show(); 
    }
    void add(Penguin p, int x, int y) { 
	this.skater = p; 	
        p.placeIn(this, x, y); 
    }
    private class WindowCloser extends WindowAdapter {
	public void windowClosing(WindowEvent event) {
	    System.exit(0); 
	}
    }
    private class Surface extends JPanel {
	int columns, rows; 
	Surface(int columns, int rows) { 
	    this.columns = columns; 
	    this.rows = rows; 
	}
	int fontSize = 10; // in pixels 
	Font digitsFont = 
	    new Font("Serif", Font.PLAIN, fontSize); 
	public void paintComponent(Graphics g) {
	    super.paintComponent(g); 
	    ((Graphics2D)g).setFont(digitsFont); 
	    g.setColor(Color.black); 
	    g.fillRect(0, 0, columns * cellWidth, rows * cellHeight); 
	    g.setColor(Color.gray); 
	    for (int i = 0; i <= rows; i++) {
		g.drawLine(0, 
                           i * cellHeight, 
                           columns * cellWidth, 
                           i * cellHeight); 
	    }
	    for (int i = 0; i < columns; i++) {
		g.drawLine(i * cellWidth, 
                           0, 
                           i * cellWidth, 
                           rows * cellHeight); 
	    } 
	    g.drawRect(0, 0, cellWidth * columns, cellHeight * rows); 
	    g.setColor(Color.gray); 
	    for (int j = 0; j < columns; j = j + 1) 
		for (int i = 0; i < rows; i++)  
		    g.drawString(i + ", " + j, 
				 j * cellWidth + 2, 
				 i * cellHeight + fontSize); 	   
	    if (skater != null) { 
		int x = skater.x, y = skater.y;
		g.setColor(Color.black); 
		g.fillRect(x, y, 31, 31); 
		skater.draw(g); 
	    }
	}
    }
} // Rink

Once you have these classes you need to create a third one (call it LabOne.java) and make its main method perform what the lab assignment is asking for (which is described above). Here are two examples, to make sure we have enough to start from.

EXAMPLE ONE: What happy() Really Means (One.java)

class One {
    public static void main(String[] args) {

	Rink ballroom = new Rink(10,  // number of columns 
				 10); // number of rows 

	/* Note the Rink created is called 'ballroom'. We'll
	   have to use this name to refer to it thereafter.*/ 

	Penguin p = new Penguin(); // create a Penguin, call it
	                           // ... 'p' (what's in a name?) 

	ballroom.add(p, 1, 7); // add the Penguin to our Rink, in 
	// column 1 and line 7 (and remember our numbering scheme)

	p.pause(); p.turnLeft(); // control the Penguin 
	/* Remember 'The Wrong Trousers' (the video)? */ 

	p.moveForward(); 
	p.moveForward(); 
	p.moveForward(); 
	p.happy(); 
	p.moveForward(); 
	p.moveForward(); 
	p.moveForward(); 
	p.pause(); 
	p.turnLeft(); 
	p.pause();        // commands are issued in sequence 

	p.moveForward(); p.moveForward(); p.moveForward(); p.happy(); 
	p.moveForward(); p.moveForward(); p.moveForward(); p.pause(); 
        
        p.turnLeft(); p.pause(); 

	p.moveForward(); p.moveForward(); p.moveForward(); p.happy(); 
	p.moveForward(); p.moveForward(); p.moveForward(); p.pause(); 

	p.turnLeft(); p.pause(); 

	p.moveForward(); p.moveForward(); p.moveForward(); p.happy(); 
p.moveForward(); p.moveForward(); p.moveForward(); p.pause(); p.turnLeft(); 
p.pause(); p.moveForward(); p.turnRight(); p.moveForward(); p.turnLeft(); p.
moveForward(); p.moveForward(); p.turnLeft(); p.turnLeft(); p.moveForward(); 
p.moveForward(); p.turnLeft(); p.turnLeft(); p.moveForward(); p.moveForward();
 p.turnLeft(); p.turnLeft(); p.moveForward(); p.moveForward(); p.turnLeft(); 
p.turnLeft(); p.moveForward(); p.moveForward(); p.turnLeft(); p.turnLeft(); 
	
        /* can you still say you know where the Penguin is right now? 

	   Remember that not only the computer reads your programs! 

	   Write your programs as if they were essays. 

	   Make your code crystal clear. 

	 */ 

        p.moveForward(); 
	p.moveForward(); 
	
	p.turnLeft(); 

	p.happy(); 

    }
}

(This really clarifies what the Penguin does when you're asking it to show that it's happy.)

EXAMPLE TWO: Staircase Improvisation (Dance.java)

class Dance {
    public static void main(String[] args) {

	Rink ballroom = new Rink(6, 6); 

	Penguin p = new Penguin();

	ballroom.add(p, 1, 4); 

	p.pause(); 

	p.turnLeft();    

        p.turnLeft();    p.moveForward(); // go left
	p.turnRight();   p.moveForward(); // go right 
	p.turnLeft();    p.moveForward(); // go left 
        p.turnRight();   p.moveForward(); // go right
	p.turnLeft();    p.moveForward(); // go left 
	p.turnRight();   p.moveForward(); // go right 
	// now stop, rotate once, stay some more 
	p.pause();       p.turnRight();   p.pause();       
	// come south three tiles 
	p.moveForward(); p.moveForward(); p.moveForward(); 
	// stop and catch your breath
	p.pause();       
	// pirouette 
	p.turnLeft();    p.turnLeft();    p.turnLeft();    p.turnLeft(); 
	// stop, for applause 
	p.pause(); 	
	// another pirouette, followed by immediate movement west 
	p.turnRight();   p.turnRight();   p.turnRight();   p.turnRight(); 
	p.turnRight();   p.moveForward(); p.moveForward(); p.moveForward(); 
	// stop 
	p.pause(); 	 
	// turn left, then stop 
	p.turnLeft(); 

	p.pause(); 
	// one final pirouette, after which just thank the audience 
	p.turnLeft(); p.turnLeft(); p.turnLeft(); p.turnLeft(); 

	p.happy(); 
	// Don't worry(), be happy(). 
    }
}

(This was a smaller program).

As a reminder, please note.

A Penguin:

can be created (and it will be facing south by default)
can be added to a Rink at a certain location (you have to ask the rink for that, though)
can be asked to turn left, or right (regardless of the direction it's facing)
can be asked to move one cell forward (regardless of the direction it's facing)

A Rink:

can be created (with the size (columns, rows) of your choice)
can hold one penguin at a time, added with add
adding a penguin to a rink is done by specifying
1. the column (vertical slices), and the
2. line (lines are horizontal rows in the rink)
in that order, in the method add.

Note though that when the Rink shows, it labels the cells by first printing the line, then the column, for each of the tile. The reason this numbering is also important is because it is the numbering used in 2 dimensional arrays in Java (of the kind we will encounter a bit later).

Note that x and y still keep the meaning that they originally had:

x is the number of columns to the left, and
y is the number of lines above (to the top)

When we create the Rink, and when we add a Penguin to it, we mention x first, and y next, almost as we do in analytical geometry. However when we refer to the table of cells that the Rink is, we can also denote the cells in the array by printing (y, x), that is, by specifying the line first, and the column next. The point being that both notations are well-established, and we need to be aware of them both. (These notes have been updated briefly on Tuesday night).

You should now write the program with no problems.

And here's a picture of Wallace and Gromit (the Aardman Penguin is pictured in disguise at the beginning of the assignment) from The Wrong Trousers to remind you of it, and for motivation.

Here also is a picture taken during Dance.java to know what to expect of it:

Last updated: Jun 13, 2001 by Adrian German for A201