Using Java from the Terminal in Mac OS X

This document instructs you on how to use Java from the Terminal in Mac OS X. The Terminal is necessary for redirecting standard input, redirecting standard output, and piping—you will use these features in Section 1.5.

These instructions apply to Mac OS X 10.4.11 and higher.

Install the Programming Environment

You will use the Java compiler javac to compile a Java program and the Java interpreter java to execute it.

Follow these instructions for installing a programming environment on Mac OS X if you have not already done so.

Command-Line Interface

You will type commands in an application called the Terminal.

The installer creates a shortcut on the desktop to the Terminal. Double-click it to launch the Terminal. You should see something like:
machine:~ username$
The ~ is shorthand for your home directory /Users/username.
To confirm that the Java compiler is installed, type the command in boldface below and check that the results match:
machine:~ username$ javac -version javac 1.6.0_26
It's important that you see the number 1.6 or 1.5 for the Java version number, but the rest is not critical.
To confirm that you the Java interpreter is installed, type the command in boldface below and check that the results match:
machine:~ username$ java -version java version "1.6.0_26" Java(TM) SE Runtime Environment (build 1.6.0_26-b03-383-11A511) Java HotSpot(TM) 64-Bit Server VM (build 20.1-b02-383, mixed mode)
Again, it's important that you see the number 1.6 or 1.5 for the Java version number, but the rest is not critical.

Compile the Program

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

From the Command Prompt, navigate to the directory containing HelloWorld.java, say /Users/username/intros/hello, by typing the cd (change directory) commands below:
machine:~ username$ cd introcs machine:~/introcs username$ cd hello machine:~/introcs/hello username$
Compile it by typing the javac command below:
machine:~/introcs/hello username$ javac HelloWorld.java machine:~/introcs/hello username$
Assuming the file HelloWorld.java is in the current working directory, you should see no error messages.

Execute the Program

You will use the java command to execute your program.

From the Command Prompt, type the java command below.
machine:~/introcs/hello username$ java HelloWorld Hello, World
You should see the output of the program — Hello, World.

Troubleshooting

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.

I deleted the desktop shortcut to Terminal. Where can I find it?

I successfully compiled HelloWorld.java with javac, but, when I execute, I get the error message "Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld". What am I doing wrong? First, verify that the file HelloWorld.class is in the current directory. Be sure to type java HelloWorld without a trailing .class or .java.

When I compile or execute a program from the Terminal that uses StdIn, I get the error .... How can I fix this? First, verify that the installer installed the standard libraries to /Users/username/introcs/stdlib.jar. If so, it is likely an issue with the CLASSPATH environment variable. From the Terminal, type the following command to display it:

machine:~/introcs username$ echo $CLASSPATH

The CLASSPATH environment variable should include /Users/username/introcs/stdlib.jar.

How do I break out of an infinite loop in the Terminal? Type Ctrl-c.

When using standard input, how do I signify that there is no more data? If you are entering input from the keyboard, type Ctrl-d for EOF (end of file).

Can I use csh or tcsh instead of bash? Yes.