Creating Java Applets using Kawa

Creating Java Applets using JCreator

Applets are designed to be included in html pages and run either by a web browser such as Netscape or Internet Explorer, or by Applet Viewer, a program that Sun supplies with Java. In either case, you have to create an html document. Since applets use graphics and are run in windows, they use java.awt. The letters awt stand for the abstract windowing toolkit. Two files in the awt must be imported into your program. These are java.awt and java.applet.Applet. They are in the Java library and the compiler will find them and include them in your program.

Create a new file as you did for an application, but this time type an applet. Notice that it extends Applet and that it does not have a main method. The paint method is used in this case to paint a picture on the screen. The methods setColor and fillRect are used to set the pen color and then to draw an oval in that color. The first two parameters in fillRect give the coordinates of the upper left hand corner of the rectangle. And the last two give the width and height of the rectangle. Type it in and save it on your disk as Rectangle.java.

// An applet with a class that draws a rectangle.

import java.awt.*;

import java.applet.Applet;

public class Rectangle extends Applet

{

public void paint (Graphics g)

{

g.setColor (Color.red); // This sets the pen color to red.

g.fillRec (100, 100, 60, 40); // This draws a rectangle with location (100, 100) and diameter 50

} // method paint

} // class Rectangle

Compile your applet and correct any errors that the compiler finds. The resulting class file can be linked into an html document using the <applet> tag. Create a new file with the following html code. Then save it as Rectangle.html.

<html>

<head>

<title>Rectangle Example</title>

</head>

<body>

<h3>Rectangle Example</h3>

</body>

</html>

Since applets are part of html pages, the html file is the one to be executed, not the java file. So when you click on the run file icon, you will bring up Applet Viewer and not the console window. The results should look like that below.

Now try changing the size and location of the rectangle and see what you get. Remember to save and compile the applet class and run the html file. You can also change the color of the rectangle. There are a number of colors recognized by the awt including Color.green, Color.orange, Color.blue, Color.cyan and Color.magenta. You can try some of these. You can also draw several rectangles by including several fillRect statements. Make sure they are located in different places or they will overlap.

Drawing circles is very similar. The command here is fillOval. The oval is defined to be the largest oval that will fit inside of the rectangle with the given location and dimensions. For example,

g.fillOval (100, 100, 50, 50);

fill draw a circle that fits inside the rectangle whose upper left hand corner is at (100, 100) and with diameter 50.

If you decide to draw a circle, save it as Circle.java and create an html file with the line

When you run this, you should see a circle at the same location as the rectangle you drew first.