Java Tech - Chapter 1 : Simple Applet

The procedure to create and run an applet goes as follows for an applet that simply displays "Hello World!" in its graphical window and also prints it to the Java console:

Step 1: Use an editor to enter the following code for HelloWorld applet:

HelloWorld Applet

public class HelloWorld extends java.applet.Applet
{
   public void paint(java.awt.Graphics g)
   {
        g.drawString("Hello World!",50,25);
        System.out.println("Hello World!");
    }
}

Save this code into a file called HelloWorld.java . (Note that the name of the file, including the case of each letter, must match exactly with the class name HelloWorld.)

Step 2: Then compile the application with*

> javac HelloWorld.java

This creates the class file

HelloWorld.class

Step 3: Next you must create a web page file to hold the applet. (If you are unfamiliar with hypertext and web pages, see the Creating Web Pages for Applets in the Chapter 1: Supplements section for a brief introduction.)

Put the following code into a hypertext file such as the following file we could call HelloWorld.html:

HelloWorld.html

<HTML>
<Head>
<Title> A Simple Program </Title>
<Body>

</Body>
</HTML>

and then put this file into the SAME directory as the HelloWorld.class file. (We will discuss later how to organize applet files into different directories.)

Step 4: We have included the applet in this web page. So opening the file HelloWorld.html in your browser will display the same as the window here.

HelloWorld.java

You can also see the "Hello World!" line in the Java Console of the browser.

An alternative way to run the applet is with appletviewer:

> appletviewer HelloWorld.html

We will discuss in later chapters the structure of Java programs, the class keyword, etc.

Tips: Finding the Java Console in the Browser

Most browsers send error messages and print outputs for applets to a Java Console window. Different browsers have different ways of opening this window.

With the new Java plug-in, the console can be activiated via the "coffee cup" icon that will appear in the right side of the Windows start toolbar after the plug-in begins to run. Just right click on it and a menu will appear from which you can pick the "Open Console" item. (You can also go to the "Advanced" tab in the Java control dialog and select the "Show console" item so that the console always appears whenever the plug-in runs.)
In the older Mozilla browser, choose Tools-> Web Developoment -> Java Console
In Netscape, choose the "tools" in the top menu, "Web Development", and then "Java Console".
In Internet Explorer you must first enable the console by choosing "Tools" menu, then "Internet Options" and then in the "Advanced" page, check "Java console enabled". Under the "View" menu you can then open the "Java console". Also, the output is sent to the c:\Windows\Java\javalog.txt file.

* On the Java Tools page, see the note on the javac -target option.

Latest update: Feb. 12, 2005