Hello, World in Java on Windows

This document instructs you on how to setup a Java programming environment for your Windows XP computer and provides a step-by-step guide for creating, compiling, and executing a Java program. Windows NT and Windows 2000 are similar, but you might need to make some minor adjustments. All of the software is freely available on the Web.

Java

You will use the Java compiler javac to compile your Java programs and the Java interpreter java to run them.

• Download the Java 2 standard edition J2SE SDK v 1.4.2_07 to the Desktop and double-click to install. (i.e., Click on Download in the SDK row and accept the License Agreement. Then, use the Windows Offline Installation. Be sure to choose the SDK, not the JRE. You don't need the NetBeans IDE cobundle.) We recommend all of the default options. Note the installation directory for later - probably something like C:\j2sdk1.4.2_07. While it's installing, you might enjoy reading Neal Stephenson's light-hearted essay In the Beginning was the Command Line.

• To make sure that Windows can find the Java compiler and interpreter,

  • Select Start -> Control Panel -> System -> Advanced -> Environment Variables -> System Variables -> Path.

  • Prepend C:\j2sdk1.4.2_07\bin; to the beginning of the Path variable.

  • Cllick OK three times.

  In Windows XP, you might need to switch to classic view instead of category view to discover all of the options. In Windows NT and 2000, select Start -> Settings -> Control Panel to get to the Control Panel.

Command Line Interface

You will type commands in an application called the Command Prompt.

• Launch the command prompt via Start -> Run and type cmd in the box. You should see the command prompt which looks something like:

  Microsoft Windows XP [Version 5.1.2600]
  (C) Copyright 1985-2001 Microsoft Corp.
  

• To check that you have the right version of Java installed, type the text in boldface below. You should see something similar to the information printed below. (Version numbers should agree with the version you downloaded.)

  
  C:\Documents and Settings\wayne>java -version
  java version "1.4.2_07"
  Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_07-b01)
  Java HotSpot(TM) Client VM (build 1.4.2_07-b01, mixed mode)
  
  C:\Documents and Settings\wayne>
  

• Now, create a directory to store your Java programs. In the window containing the Command Prompt, type the bold commands below:

  C:\Documents and Settings\wayne>cd c:\
  C:\>mkdir introcs
  C:\>cd introcs
  C:\introcs>mkdir hello
  C:\introcs>cd hello
  C:\introcs\hello>
  

  The mkdir command creates a new directory; the cd command changes the current working directory. After executing these commands, your working directory is the newly created C:\introcs\hello. All of your files for Assignment 0 will go here. Don't be scared by the Command Prompt - you will only need to use a few basic commands. Keep this window open since you will need it later in the assignment.

• Since you will be using the Command Prompt frequently, we recommend customizing the default settings. Right-click the title bar of an open Command Prompt window, select Properties and then:

  • Set Layout -> Screen Buffer Size to 80 x 500.

  • Select Options -> Edit Options -> QuickEdit Mode.

  • Select Options -> Edit Options -> Insert Mode.

  Click OK and check Save properties for future windows with same title to make the changes permanent.

Text Editor

You will type and edit your programs in a text editor called JEdit. JEdit is similar to conventional word processors like MS Word and Notepad, but it features many specialized programming tools including syntax highlighting, bracket matching, auto indenting, indent shifting, line numbering, and commenting out code. It's even written in Java.

• Download the latest stable version of JEdit using the Windows installer, and install it using the default options.

• We strongly recommend the following JEdit customizations.

  • Change the default indentation to 4 spaces via Utilities -> Global Options -> Editing -> Indent Width and Utilities -> Global Options -> Editing -> Tab Width.

  • Change the default tab width when printing to four spaces via Utilities -> Global Options -> Printing -> Tab width when printing

  • Add line numbers by checking Utilities -> Global Options -> Gutter -> Line Numbering

  • Allow at most 80 characters per line by Utilities -> Global Options -> Editing -> Word wrap -> hard and Utilities -> Global Options -> Editing -> Wrap margin -> 80.

  • Change the default line separator to Unix via Utilities -> Global Options -> General -> Default Line Separator

  • Remove the annoying . that marks the end of a line by unchecking Utilities -> Global Options -> Text Area -> End of Line Markers

Now you are ready to write your first Java program.

• Launch JEdit Start -> jEdit.

• In the JEdit window, type the Java program exactly as it appears below. If you omit even a semicolon, the program won't work.

  public class HelloWorld { 
     public static void main(String[] args) { 
          System.out.println("Hello, World");
     }
  }
  

• When you're done, save the program using File -> Save As, choose the directory C:\introcs\hello and type in the file name HelloWorld.java. The file name is case sensitive and must exactly match the name of the class in the Java program.

• To associate .java files with JEdit so that when you double-click a .java file, it opens it in JEdit:

  • Right click a .java file (or left-click, then shift-right click it if using Windows NT).

  • Choose Open With...

  • Select JEdit from the list of programs or locate JEdit by selecting Other if necessary.

  • Check the Always use this program to open this file type box

Compile the Program

It is now time to convert your Java program into a form more amenable for execution on a computer.

• From the Command Prompt, type

  C:\introcs\hello\>javac HelloWorld.java

  If javac complains in some way, you mistyped something, and you should check your program carefully. Ask for help if you can't see the mistake.

• If everything went well, you should see the following in the Command Prompt:

  C:\introcs\hello\>javac HelloWorld.java
  C:\introcs\hello\>
  

  Silence is golden in computer science.

Execute the Program

Now it is time to run your program. This is the fun part.

• At the Command Prompt, type

  C:\introcs\hello\>java HelloWorld

• If all goes well, you should see

  C:\introcs\hello\>java HelloWorld
  Hello, World

• You may need to repeat this edit-compile-execute cycle a few times before it all goes smoothly. Use the up and down arrow keys to repeat previous commands and avoid extra typing.

Troubleshooting

Here are a few suggestions that might help correct any installation woes you are experiencing. If none of these options work (or you don't understand how to follow them), email a staff member.

I can't install JEdit. When I double-click the .jar file, it's not associated with any programs. What can I do? First, make sure that Java 1.4.2 is installed. Then, when it prompts you for an application to associate to .jar files, select "Java". Alternatively, from the command prompt, cd to the directory containing .jar file and execute the program as follows:

cd C:\Downloads
java -jar jedit42install.jar

When I type, "java -version" I get an error. Check that you edited your Path environment variable as indicated. Close and re-open a command prompt. Type path at the command prompt and look for an entry that includes C:\j2sdk1.4.2_07\bin;. Check that the version number 1.4.2_07 matches the one you installed since Sun updates Java periodically and you might have a more recent version. If this doesn't fix the problem, check if you have any old versions of Java on your system. If so, un-install them and re-install Java.

The command "java -version" works, but not javac. Any thoughts? It's probably a path issue. Try the suggestions from the previous question.

I can compile with javac, but I get the error message "Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld" when I try to execute it with java. First, be sure that HelloWorld.java is in the current directory. The, check your environment variables (system or user) for an entry labeled Classpath. Delete it, close your command prompt, re-open it, and try to execute your program.

I followed the instructions above for associating .java files with JEdit, but it doesn't work on my system. How can I fix it? Do the following steps.

• Open an Explorer window and click Tools -> Folder Options
• Go to the File Types tab and select the JAVA extension.
• Click Advanced.
• Select open from the Actions selection box, then click edit.
• In the box labeled Application used to perform action type the following, adapted for your appropriate path names:

  "C:\j2sdk1.4.2_07\bin\javaw.exe" -jar "C:\Program Files\jEdit\jedit.jar" %1
  

If you get a Restore button instead of Advanced, click it and it becomes Advanced.

Can I use Windows 98 or ME? Yes, but we strongly discourage you from doing so since they're rather unstable operating systems. You need to modify a few of the instructions. To get a command prompt, type command instead of cmd. To modify your path, edit the file C:\AUTOEXEC.BAT, perhaps under the supervision of a lab TA. You will need to reboot before the changes take effect.