Using Java

I am going to assume that you have used Java already in earlier courses and within a Unix environment. For the moment, therefore, I limit myself to the following comments:

To use the system on our local cluster, you have to load the module java. If you are new to the UMN setup and don't know about modules and how to load them, you can find some information about this in the system help pages; with specific regard to modules, you may look here.

As you probably know already, Java programs run on a virtual machine. Thus, to execute these programs, you first compile them, producing a byte code file that you then execute using a virtual machine emulator or a byte code interpreter.

To clarify the latter point, suppose you have stored the following Java program in a file called HelloWorld.java:

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

You would then compile this using the command

% javac HelloWorld.java %

Read % as the prompt symbol here. As indicated, the compilation would end without errors in this case and will produce a bytecode file in HelloWorld.class. To execute this code, you would invoke the following command with the accompanying results:

% java HelloWorld Hello World %

In general, your code will build on class definitions available from other locations. To permit the use of such definitions, you have to set the CLASSPATH variable to include all the relevant paths. I assume that you are familiar with these details. If not, ask a question about it on the class discussion forum and someone will help you out.

CSci 5106: Programming Languages