Appendix 2:

Some Notes on Java Programming Environments

EACH TIME I HAVE TAUGHT a course based on this textbook, I have used a different programming environment: CodeWarrior for Macintosh, Visual J++ for Windows, and the JDK for Linux. Of the three development environment environments, the JDK was by far the most successful. CodeWarrior and Visual J++ are examples of integrated development environments. That is, they include a text editor, an interactive debugger, a compiler, and tools for managing large programming projects. The problem with such environments in an introductory course is their complexity, which can be overwhelming for a beginner who is having trouble enough learning the basics of programming. The JDK (Java Development Kit) uses a command-line interface, in which the user types commands to compile and run Java programs. Although this interface is a bit alien to students who are used to working with a graphical user interface, I have not run into any students who had difficulty understanding or using it. Another advantage of the JDK is that it is free.

In this appendix, I'll give some information and opinion on Java programming environments for Windows, Macintosh, and Linux/UNIX. I'll concentrate on free software, including the JDK. There is a lot of redundancy among the sections on Windows, Macintosh, and Linux/UNIX. You probably only need to read one of these sections.

But first, let me describe the computing setup that I use in my courses, since that might be of interest to other professors.

My department has a small computing lab of its own, with a mixture of Linux, Windows, and Macintosh computers. The majority of the computers run Linux. The Linux computers use a graphical ("XDM") login screen and the KDE desktop, which means that they work much the same as Windows or Macintosh from the user's point of view. The lab is not large enough for introductory programming classes, but students can log on to the Linux machines in the lab from any Windows computer on campus. For this, we use X-Win32, from StarNet (www.starnet.com). Using X-Win32, students see the same login screen and desktop as they see when they work on the machines directly in the lab. (Although X-Win32 is fairly expensive for commercial use, StarNet has a very reasonable academic pricing policy.) Student home directories are on a deparmental server, and are accessible from anywhere on campus. The Linux distribution that we use, currently SuSE 6.1, provides many tools that we use in introductory programming and other courses, including the JDK, text editors, C++, Lisp, Prolog, and OpenGL (in the form of Mesa).

Sources of Software and Information

If you work in Windows, I suggest that you take a look at burks.brighton.ac.uk. You'll find a large collection of Windows software that is useful for students of computer science. The collection can be purchased on a set of cheap CD's, and it is available on-line at http://burks.brighton.ac.uk/burks/index.htm. (Version 4 of this collection includes the second edition of this textbook. It also has a copy of JDK 1.1.6, which is suitable for use with this textbook.)

The home site for Java, which was invented by Sun Microsystems, is java.sun.com. For version 1.1 of the Java Development Kit see http://java.sun.com/products/jdk/1.1/. Version 1.2 is at http://java.sun.com/products/jdk/1.2/. (This textbook requires JDK version 1.1 or higher. Version 1.2 is a much larger download.)

For information about programming in Java on Macintosh computers, see http://developer.apple.com/java/.

A good general source for Java programming information is www.gamelan.com.

Text Editors

Before you start writing programs, make sure that you have a good text editor. A programmer's text editor is a very different thing from a word processor. Most important, it saves your work in plain text files and it doesn't insert extra carriage returns beyond the ones you actually type. A good programmer's text editor will do a lot more than this. Here are some features to look for:

There are many free text editors that have some or all of these features.

For Linux and UNIX, I recommend nedit as a nice editor and one that will be comfortable for people who are used to GUI programs for Windows and Macintosh. It has all the above features, except a function menu. If you are using Linux, it is likely that nedit is included in your distribution, although it may not have been installed by default. It can be downloaded from http://www.nedit.org/ for many UNIX platforms. Features such as syntax coloring and autoindentation are not turned on by default. You can configure them in the Options menu. Use the "Save Options" command to make the configuration permanent.

For Macintosh, I recommend BBEdit Lite from Bare Bones Software. BBEdit Lite is a free version of the excellent text editor, BBEdit. It can be downloaded at http://www.barebones.com/free/bbedit_lite.html. You can also ftp to ftp://ftp.barebones.com/pub/freeware/ and download BBEdit_Lite_4.6.hqx. This version requires System 7 or higher. (You will need Stuffit Expander to extract the application from the hqx file. You probably already have Stuffit Expander, since it comes with most Web browsers. If not, you can download it from www.aladdinsys.com.) You might also want to download PopupFuncs_2.8.2.hqx from the same ftp directory. PopupFuncs can be used to add pop-up function menus to BBEdit Lite. Unfortunately, the free version of BBEdit does not do syntax coloring.

In Windows, I have used Editeur, but it is shareware rather than freeware. (However, I haven't used Windows enough to have a strong recommendation for an editor.)

Java users on any platform who are using Java 1.3 might want to take a look at JEdit (http://www.jedit.org), a free advanced programmers text editor written entirely in Java.

Java for Windows 95 or NT (or later)

If you use the JDK on Windows 95/98, you will be working in DOS command windows, with a command-line interface. A utility called "doskey", which is included in the standard Windows installation, will make your life easier. To install it, add the line

doskey

to your autoexec.bat file. The change will take effect when you restart your computer. Once doskey is installed, when you are working in a DOS command window, you can use the up arrow key to go back to previous commands that you have typed in that window. Once the command is retrieved, you can edit it, if you want. Then press return to issue the command again. Since you will often find yourself issuing the same commands over and over as you compile and run your programs, this can save you a lot of typing.

Note: To edit your autoexec.bat file, select the "Run" command from the "Start" menu. Enter the command sysedit in the dialog that pops up, and press return. This will open a window where you can edit system configuration files, including autoexec.bat. Make your change, such as adding the "doskey" command to this file, and save your changes.

You can download version 1.1 of the JDK for Windows at http://java.sun.com/products/jdk/1.1/. You might also want to pick up a copy of the documentation there. JDK 1.1.6 is also available on the Burks site (http://burks.brighton.ac.uk/burks/index.htm). You should be able to use a later version of the JDK with this textbook, but not an earlier one. Follow the installation instructions. This will include modifying your PATH to include the directory that contains the java compiler and interpreter. (On Windows 95/98, you will have to edit your autoexec.bat file and restart your computer to do this. See the above note about editing autoexec.bat. You have to add the path for the bin directory of the java installation to the end of the line that starts "SET PATH=". If there is no such line in the autoexec.bat file, add one. The path to the bin directory will be something like C:\jdk1.1.6\bin if you used the default JDK installation. The line in the autoexec.bat file will have the form: "SET PATH=%PATH%;maybe-other-paths;C:jdk.1.6\bin".)

Make a directory to hold your Java programs. (You might want to have a different subdirectory for each program that you write.) Create your program with a text editor, or copy the program you want to compile into your program directory. If the program needs any extra files, don't forget to get them as well. For example, most of the programs in the early chapters of this textbook require the file TextIO.java. You should copy this file into the same directory with the main program file that uses it. (Actually, you only need the compiled file, TextIO.class, to be in the same directory as your program. So, once you have compiled TextIO.java, you can just copy the class file to any directories where you need it.)

If you have downloaded a copy of this textbook, you can simply copy the files you need from the source directory that is part of the download. If you haven't downloaded the textbook, you can open the source file in a Web browser and the use the Web browser's "Save" command to save a copy of the file. Another way to get Java source code off a Web browser page is to hilite the code on the page, use the browser's "Copy" command to place the code on the Clipboard, and then "Paste" the code into your text editor. You can use this last method when you want to get a segment of code out of the middle of a Web browser page.

To use the JDK, you will have to work in a DOS window, using a command-line interface. Open a DOS Window and change to the directory that contains your Java source code files. (Tip: In Windows 95/98, open a directory window for the directory, then select the "Run" command from the "Start" menu, enter "command" in the dialog window that pops up, and press return. A DOS window will open that is all set for working in the directory shown in the directory window.)

The "javac" command is used for compiling Java source code files. For example, to compile the Java source code file named SourceFile.java, use the command

javac SourceFile.java

You must be working in the directory that contains the file. If the source code file does not contain any syntax errors, this command will produce one or more compiled class files. If the compiler finds any syntax errors, it will list them. Note that not every message from the javac compiler is an error. In some cases, it generates "warnings" that will not stop it from compiling the program. If the compiler finds errors in the program, you can edit the source code file and try to compile it again. Note that you can keep the source code file open in a text editor in one window while you compile the program in a DOS window. Then, it's easy to go back to the editor to edit the file. However, when you do this, don't forget to save the modifications that you make to the file before you try to compile it again! (Some text editors can be configured to issue the compiler command for you, so you don't even have to leave the text editor to run the compiler.)

If your program contains more than a few errors, most of them will scroll out of the window before you see them. In Windows NT only, but not Windows 95/98, yoiu can save the errors in a file which you can view later in a text editor. Use the command such as

javac SourceFile.java >& errors.txt

The ">& errors.txt" redirects the output from the compiler to the file, instead of to the DOS window. For Windows 95/98 I've written a little Java program that will let you do much the same thing. See the source code for that program, cef.java, for instructions.

It is possible to compile all the Java files in a directory at one time. Use the command "javac *.java".

(By the way, all these compilation commands only work if the classes you are compiling are in the "default package". This means that they will work for any example from this textbook.)

Once you have your compiled class files, you are ready to run your application or applet. If you are running a stand-alone application -- one that has a main() routine -- you can use the "java" command from the JDK to run the application. If the class file that contains the main() routine is named Main.class, then you can run the program with the command:

java Main

Note that this command uses the name of the class, "Main", not the full name of the class file, "Main.class". This command assumes that the file "Main.class" is in the current directory, and that any other class files used by the main program are also in that directory. You do not need the Java source code files to run the program, only the compiled class files. (Again, all this assumes that the classes you are working with are in the "default package".)

If your program is an applet, then you need an HTML file to run it. See Section 6.2 for information about how to write an HTML file that includes an applet. As an example, the following code could be used in an HTML file to run the applet "MyApplet.class": 

               <applet code="MyApplet.class" width=300 height=200>
               </applet>

The "appletviewer" command from the JDK can then be used to view the applet. If the file name is test.html, use the command

appletviewer test.html

This will only show the applet. It will ignore any text or images in the HTML file. In fact, all you really need in the HTML file is a single applet tag, like the example shown above. The applet will be run in a resizable window, but you should remember that many of the applet examples in this textbook assume that the applet will not be resized. Note also that your applet can use standard output, System.out, to write messages to the DOS window. This can be useful for debugging your applet.

Of course, it's also possible to open the HTML file in a Web browser, such as Netscape or Internet Explorer. One problem with this is that if you make changes to the applet, you have to actually quit the browser and restart it in order to get the changes to take effect. The browser's Reload command might not cause the modified applet to be reloaded.

Java for Macintosh

The Apple Computer company has a free Software Development Kit (SDK) for Java. This SDK includes Apple's versions of the compiler from the JDK. To use the SDK, you also need to have a copy of the MRJ (Macintosh Runtime for Java) installed on your computer. The MRJ includes a Java interpreter for running Java applications and applets. If you have a recent version of the MacOS, the MRJ might already be installed. If not, you can download it from Apple's Java Web site at http://www.apple.com/java/. The SDK can be downloaded from the FTP directory at

ftp://ftp.apple.com/developer/Development_Kits/

At the time I am writing, the latest version is MRJ_SDK_2.2_Install.sit.hqx. For more links and full information on developing Java programs on Macintosh, see http://developer.apple.com/java/.

You'll need access to three programs from the MRJ and SDK. I suggest that you make aliases to these programs and leave the aliases on your desktop. (To make an alias, click once on the program icon to hilite it. Choose the "Make Alias" command from the file menu. This will create an icon for the alias. Drag this icon onto your desktop.) The programs you need are:

Make a folder to hold your Java programs. (You might want to have a different folder for each program that you write.) Create your program with a text editor, or copy the program you want to compile into your program folder. If the program needs any extra files, don't forget to get them as well. For example, most of the programs in the early chapters of this textbook require the file TextIO.java. You should copy this file into the same folder with the main program file that uses it.

If you have downloaded a copy of this textbook, you can simply copy the files you need from the source folder that is part of the download. If you haven't downloaded the textbook, you can open the source file in a Web browser and the use the Web browser's "Save" command to save a copy of the file. Another way to get Java source code off a Web browser page is to hilite the code on the page, use the browser's "Copy" command to place the code on the Clipboard, and then "Paste" the code into your text editor. You can use this last method when you want to get a segment of code out of the middle of a Web browser page.

To compile a Java source code file drag the file onto the javac program icon (or an alias for this program). If the file you are compiling depends on other source code files, select them all and drag them all onto the javac icon. For example, if your program uses TextIO, you should drag both TextIO.java and the source file for the main program onto the javac icon. (To select multiple files, hold down the Shift key as you click on the second, third, ... files.) A dialog window will open. It should show the names of the source code files in a box on the upper left. Click the "Do Javac" button in this window. This will do the compilation. A message window will open with messages from the compiler. If your program contains any syntax errors, they will be listed in the message window. You can then edit the file and try to compile it again. Note that you can keep the text editor window and the javac window open at the same time. After making changes to the program with the text editor, save your work and hit the "Do Javac" button again.

Once you have the compiled class files, you can run your program. If the program is a stand-alone application, with a main() routine, you can run it with JBindary. Drag the compiled class file that contains the main() routine onto the JBindary icon (or an alias). Even if the main program depends on other classes, you only have to drag one file onto the icon. (However, the other class files must be in the same directory with the main class file.) A window should open that shows the name of your main class in a box at the upper left. This window also has two pop-up menus for "redirecting" Standard Input and Standard Output. For programs that use TextIO, make sure that both of these pop-up windows are set to the "Message Window". Click the "Run" button to run your program. A separate "Message Window" will open for doing standard input and output, if your program uses them.

If your program is an applet, then you need an HTML file to run it. See Section 6.2 for information about how to write an HTML file that includes an applet. As an example, the following code could be used in an HTML file to run the applet "MyApplet.class": 

               <applet code="MyApplet.class" width=300 height=200>
               </applet>

To run the applet, drag the HTML file onto the Apple Applet Runner icon (or an alias).

This will only show the applet. It will ignore any text or images in the HTML file. In fact, all you really need in the HTML file is a single applet tag, like the example shown above. The applet will be run in a resizable window, but you should remember that many of the applet examples in this textbook assume that the applet will not be resized. Note also that your applet can use standard output, System.out, to write messages. These will appear in a separate "Message Window". This can be very useful for debugging.

Java for Linux/UNIX

Hopefully, Java is already installed on your UNIX or Linux system -- or at least is available on your installation disks. For Solaris and some versions of Linux, you can download the JDK from http://java.sun.com/products/jdk/1.2/. Version 1.1 of the JDK for Solaris, but not Linux, is available at http://java.sun.com/products/jdk/1.1/. You can also check the Blackdown organization at www.blackdown.org. They produced a port of Java to Linux.

Make a directory to hold your Java programs. (You might want to have a different subdirectory for each program that you write.) Create your program with a text editor such as nedit, or copy the program you want to compile into your program directory. If the program needs any extra files, don't forget to get them as well. For example, most of the programs in the early chapters of this textbook require the file TextIO.java. You should copy this file into the same directory with the main program file that uses it. (Actually, you only need the compiled file, TextIO.class, to be in the same directory as your program. So, once you have compiled TextIO.java, you can just copy the class file to any directories where you need it.)

If you have downloaded a copy of this textbook, you can simply copy the files you need from the source directory that is part of the download. If you haven't downloaded the textbook, you can open the source file in a Web browser and the use the Web browser's "Save" command to save a copy of the file. Another way to get Java source code off a Web browser page is to hilite the code on the page, use the browser's "Copy" command to place the code on the Clipboard, and then "Paste" the code into your text editor. You can use this last method when you want to get a segment of code out of the middle of a Web browser page.

You will need a command-line interface to work with the JDK commands. If you are working with a graphical user interface, open an xterm (or other command-line window). Of course, you need the GUI to run Java applets. Change to the directory that contains your Java source code files.

The "javac" command is used for compiling Java source code files. For example, to compile the Java source code file named SourceFile.java, use the command

javac SourceFile.java

You must be working in the directory that contains the file. If the source code file does not contain any syntax errors, this command will produce one or more compiled class files. If the compiler finds any syntax errors, it will list them. You should have some way of scrolling back to see the first errors in the list. Note that not every message from the javac compiler is an error. In some cases, it generates "warnings" that will not stop it from compiling the program. If the compiler finds errors in the program, you can edit the source code file and try to compile it again. Note that you can keep the source code file open in a text editor in one window while you compile it in another. Then, it's easy to go back to the editor to edit the file. However, when you do this, don't forget to save the modifications that you make to the file before you try to compile it again!

It is possible to compile all the Java files in a directory at one time. Use the command "javac *.java".

(By the way, all these compilation commands only work if the classes you are compiling are in the "default package". This means that they will work for any example from this textbook.)

Once you have your compiled class files, you are ready to run your application or applet. If you are running a stand-alone application -- one that has a main() routine -- you can use the "java" command from the JDK to run the application. If the class file that contains the main() routine is named Main.class, then you can run the program with the command:

java Main

Note that this command uses the name of the class, "Main", not the full name of the class file, "Main.class". This command assumes that the file "Main.class" is in the current directory, and that any other class files used by the main program are also in that directory. You do not need the Java source code files to run the program, only the compiled class files. (Again, all this assumes that the classes you are working with are in the "default package".)

If your program is an applet, then you need an HTML file to run it. See Section 6.2 for information about how to write an HTML file that includes an applet. As an example, the following code could be used in an HTML file to run the applet "MyApplet.class": 

               <applet code="MyApplet.class" width=300 height=200>
               </applet>

The "appletviewer" command from the JDK can be used to view an applet from an HTML file. If the file name is test.html, use the command

appletviewer test.html

This will only show the applet. It will ignore any text or images in the HTML file. In fact, all you really need in the HTML file is a single applet tag, like the example shown above. The applet will be run in a resizable window, but you should remember that many of the applet examples in this textbook assume that the applet will not be resized. Note also that your applet can use standard output, System.out, to write messages to the command-line window. This can be useful for debugging your applet.

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