Lab Warm-up: Running and Compiling an Applet

This is a warm-up so you can experiment with java.  This exercise also shows you how to construct java applets, and embed them in a webpage.

Blinking Text

alt="Your browser understands the <APPLET> tag but isn't running the applet, for some reason." Your browser is completely ignoring the <APPLET> tag!
The source.

Most of the programs that we will write for this class will be stand-alone programs. However, Java also enables a way to write Applets which are programs that run through a browser. For this lab warm-up you can learn how to create java applets and incorporate them into a webpage. The applet you will compile and use is the blinking text applet above. This will also get you familiar with whatever java programming environment you choose to use so you can just start on the first programming assignment next week with all these details worked out.

For this lab you should turn in the java applet you designed and a link to a webpage with this applet running. To turn in it, log in to the UCI Electronic Educational Environment, and upload (1) your applet and (2) a link to your webpage.

Getting Accounts

In order to do this lab, you will need two different accounts: your Windows account and and a UNIX account. The Windows account is the one you will primarily be using for this class. The UNIX account will be important for having your web page and will provide some disk space for you to save files. Instructions for getting your accounts can be found at .

Accessing Files

The icon labeled youruserid on `octavian'(H:) is your file system on the Suns. All your files on your Sun account can be accessed through your Windows account by clicking on this icon. For the machines in the lab, you can not write to any files on the hard drive (labelled C: ) except for the folder C:\temp . I recommend storing all the files you are working on in your Sun account. However, while you are working on them, move them over to C:\temp .

Save and Compile the Applet Source Code

Save the source code for the blinking applet using the source code above. Compile the the source code using whatever programming environment you choose to use. Detailed instructions on how to do this using BlueJ are given below. Atfer you have compiled the code, you will have a class called Blink.class .

Making a web page

In order to have a web page that is publicly viewable, it needs to reside in a special directory on your Unix account. You also need to take care to have the protection on the directory and files set so that they can be accessed. For a quick tutorial on some Unix basics, visit , but the following list of commands should be enough for this lab:
  1. Telnet/logon to your Unix account
  2. Make a directory called public_html under the root directory
  3. Change the mode of the public_html directory to be world-readable and world-executable.
  4. Create a web page. Call it index.html and store it in your public_html directory. Instructions on how to create a web page can be found at . You can use the make_my_web program or get more creative on your own.
  5. Copy your Blink.class file to your public_html directory. You can do this using Windows Explorer. Your Unix files are all stored under the H: drive.
  6. Change the mode of the index.html and Blink.class files to be world-readable.
  7. Edit your index.html file and add lines in html to point to and execute the Blink.class file. Note that you can save the web page you are reading and view it using Notepad to see how this is done. You need the lines inbetween the <hr> commands.
  8. Test your Applet by going to the URL
  9. Change the java applet we give you in some creative way.  After all, this is your UCI webpage now, so you dont want it to be lame...

Creating a Project through BlueJ

Java Applets are programs that can be run through a web browser. This section will guide you through two different ways of running an Applet: through a web browser or through BlueJ. In order to run any program or Applet through BlueJ, you have to first create a project and put the appropriate files in the project. This is something that is required by BlueJ, and is its way of organizing files for a particular application.

Start out by opening up BlueJ through the Start menu. ( All the machines in the lab already have BlueJ installed. If you would like to install BlueJ on your own computer visit . ) Since we are creating a new project, pull down the Projects menu in BlueJ and choose New Project. Select the location where you want your project to reside and give your project a name. This will create a folder with that name and two additional files in the folder.

To run a Java Applet through a web browser, you will need at least two different files: an html file and at least one file containing the Java bytecode for the applet. The name of the html file will always have the extension .html and the names of the files containing the Java bytecode will always have the extension .class . The .class file is created by compiling Java source code which will be stored in files ending in .java . Copy the file into your project folder.

If we want to run the Applet through BlueJ, we need to add the new Java source file to the project. From the Edit menu in BlueJ, select Add Class From File. Select and click Add . A box with the name of the applet (Blink) will appear in your window. Click on the Compile button to compile the project. This will produce a file called Blink.class in the project folder which is the Java bytecode for the applet.

To run the applet, right click on the box with Blink applet and select Run Applet . You can run the applet through the applet viewer or the web browser. Experiment with both. For now, select one and click OK . When you run the Applet, BlueJ automatically produces an html file that points to the bytecode file for that applet.

If you right click on the Blink applet and select Open Editor you can edit the java source code. You will need to do this when you develop your own Java programs. Go in and edit the text that is blinking in the applet.

Go back to the folder containing the files for your project. If you double-click on the Blink.html file, your browser will open and display your new applet. If you open the html file with a text editor, you can see and edit the html file. Note the line that points to the Blink.class file. This tells the browser to execute this bytecode.