Draw a diagram showing the name of your class

Chandler-Gilbert Community College Spring 2005

Draw a diagram showing the name of your class. Think of what it should know and what it should be able to do.

Class Name

Know:

Do:

Examples:

Paycheck

Know:

	Hours worked
	Pay rate
	Payee
	Date

Do:

	Calculate gross pay
	Print itself*

Monster

Know:

	x, y coordinates
	size
	eye color
	body color

Do:

	run
	jump
	growl
	become angry
	display itself*

*Objects are responsible for displaying or printing themselves.

Use Textpad to create your class
import java.awt.* // awt needed because monster must display self
Public Class Monster { //Monster is the Class name, taken from the
} //top of your diagram.

Save ClassName.java

Create instance variables to hold what objects instantiated from your Class will know. Think carefully about the data type for each variable. These variables form Class' attributes. Attributes must be protected from other programmers. Set the security to private. Do not set the value of your attributes when you declare them. Example:
private int xCoord;
private int yCoord;
private int size; //in pixels
private Color eyeColor; //data type of color variable is the Color class.
private Color bodyColor;

Create blank methods for what your Class will know. Think carefully about whether the method should be void or will return a value.
public void run() {
}
public void jump() {
}
public void growl() {
}
public void becomeAngry() {
}
public void display() {
}

Create a special Constructor method that is used to set the initial values of the attributes. Constructor methods don't specify the security or the datatype and must have the same name as the class. Think carefully about what values you will allow users of your class to specify. You'll need to include these values as parameters. Example:
Monster(int desired XCoord, int desired YCoord, int desiredSize) {
    xCoord = desiredXCoord;
    yCoord = desiredYCoord;
    size = desiredSize;
    eyeColor = Color.red; // I decided not to allow the user to set the colors
    bodyColor = Color.black;
}

Implement you class' methods by writing the code for them. Where necessary, specify any parameters the user will need to pass to your method for it to work. Wherever possible, use your class' attributes. Example of implementing the display method:
public void display(Graphics g) {
    // BODY
    g.setColor(bodyColor);
    int monsterWidth = size;
    int monsterHeight = size * 2 / 3;
    g.fillOval(x, y, monsterWidth, monsterHeight);

    // EYES
    g.setColor(eyeColor);
    int eyeWidth = monsterWidth / 10;
    int eyeHeight = eyeWidth * 2 / 3;
    int eye1X = x + monsterWidth / 6;
    int eye1Y = y + monsterHeight / 3;
    g.fillOval( eye1X, eye1Y, eyeWidth, eyeHeight );
    int eye2X = eye1X + monsterWidth / 2;
    int eye2Y = eye1Y;
    g.fillOval( eye2X, eye2Y, eyeWidth, eyeHeight );
}

Compile your Class. You CAN'T USE YOUR CLASS IN ANOTHER PROGRAM UNLESS YOU COMPILE IT FIRST. If you make changes to your class, you will need to compile it again.

Save your class and open a second copy of textpad. Create an Applet program to instantiate an object from your class and make it do things. Example:
import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;
public Class MonsterController extends Applet{
   Monster fred; //declare variable to hold the object you will instantiate
       public void init() {
        /* new instantiates (creates) the object from your class pattern.
            At the time your object is instantiated, java runs it's       constructor
            method, passing it the parameters in parentheses. */

        fred = new Monster(50, 50, 75);
        //fred now exists and you can execute his methods, making him do tricks
}
    public void paint(Graphics g) {
        fred.display(g); // displays fred
        fred.growl(); // makes fred growl

    }
}

Save your Applet in the same folder as your Class. Compile your Applet. Run your Applet (NOT your class) and admire it. If it doesn't work, you may need to make changes to either your Class or your Applet or both.

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