Java and the Windows Command Prompt

This page is obsolete.

This document instructs you on how to use the Windows Command Prompt with Java. These instructions are specialized to Windows 7, but are similar for Windows XP and Windows Vista.


You will use the Java compiler javac to compile your Java programs and the Java interpreter java to run them. You should skip the first step if Java is already installed on your machine.

Command-line interface

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

Compile the Program

You will use the javac command to convert your Java program into a form more amenable for execution on a computer.

Execute the Program

You will use the java command to execute your program.

Input and Output

If your program gets stuck in an infinite loop, type Ctrl-c to break out.

If you are entering input from the keyboard, you can signify to your program that there is no more data by typing Ctrl-z for EOF (end of file). On some DOS systems the first line of output sent to the screen after you enter EOF will be rendered invisible by DOS. This is not a problem with your code, but rather a problem with DOS. To help you debug your program, we recommend including an extra System.out.println(); statement before what you really want to print out. If anyone knows of a better fix, please let us know!


Here are a few suggestions that might help correct any installation woes you are experiencing. If you need assistance, don't hesitate to contact a staff member.

When I type, "java -version" I get an error. Check that you edited your PATH environment variable as indicated. A missing ; or an added % is enough to screw things up. Close and re-open a command prompt. Type path at the command prompt and look for an entry that includes C:\Program Files\Java\jdk1.6.0_27\bin;. Check that the version number 1.6.0_27 matches the one you installed—Oracle 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 -version". Any thoughts? It's likely a path issue. Try the suggestions from the previous question. Also check that you installed the JDK properly by checking that the folder C:\Program Files\Java\jdk1.6.0_27\bin exists.

How can I check the values of my PATH variable? Type the following at the command prompt.

C:\introcs\hello\> echo %PATH%
The PATH variable should begin with C:\Program Files\Java\jdk1.6.0_27\bin; Be sure to open the command prompt after you have edited the PATH environment variable. You may also need to reboot for the environment variable change to take effect.

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.class is now in the current directory. Be sure to type java HelloWorld without a trailing .class or .java. Check that the command "java -version" works. Now try to execute with "java -cp . HelloWorld". If this works, you need to edit your classpath. (iTunes has a proclivity for changing the classpath, so if you recently upgraded iTunes, this is likely the source of the problem.)

Where can I learn more about the Windows command line? Here is a short tutorial on the Windows command prompt. Microsoft maintains a complete command line reference.

How do I change my directory to the H: drive from the Windows Command Prompt? Type H: at the command prompt. Then cd to the appropriate directory.