Getting started with Java

Here are some steps to get started using Java on the instructional systems. Java deals with multiple files and directories a bit more intelligently than C, which is good, but it means there's some extra organization you have to do to get set up.

The first thing you need to do is be logged in to the right system. For this course, the official Java machines are the alphas - orcas and sanjuan. Java is in fact available on a wide variety of machines throughout the department, but in varying configurations. I won't be responsible for getting you up and running if you're not planning to use the alphas for this course.
Now, you should edit your configuration, that is the .mycshrc file in your home directory. You need to tell Java where some important files are. In particular, you need to add the following three lines:
setenv JAVA_HOME /uns/usr/jdk setenv CLASSPATH $JAVA_HOME/classes:/homes/iws/csk/Java setenv LD_LIBRARY_PATH $JAVA_HOME/lib/alpha_osf32c
Of course, you should replace /homes/iws/csk/Java with the location of the directory hierarchy in which you intend to put your Java code.
Next, you should actually cause those lines to be executed. You can do this with the command source ~/.mycshrc, or you can log out and in again.

Java should now work for you. To test it out, try writing the following program. Put the files in the directory specified in your CLASSPATH.

In the file PrintMessage.java, put the following:

             public class PrintMessage
             {
                 private String message;

                 public PrintMessage( String message ) 
                 {
                     this.message = message;
                 }

                 public void print()
                 {
                     System.out.println( message );
                 }
             }

Then, in the file HelloWorld.java, put the following:

            public class HelloWorld
            {
                public static final void main( String[] args ) 
                {
                    PrintMessage msg = new PrintMessage( "Hello, World!" );
                    msg.print();
                }
            }

Note that the names of the classes correspond to the names of the files they're in. This is important!

Next, you should try compiling and running this example program. In the same directory, compile the program using the command javac HelloWorld.java. This should create two new files, HellowWorld.class and PrintMessage.class, which are like object files in C.
Finally, try running the program. To run a Java program, you use the executable java and pass it as a first argument the particular class you want to start with. So, in this case, you'd execute java HelloWorld.
That's all there is to it! If this doesn't work, send email.