Espresso: A Concentrated Introduction to Java

Java in the MathLAN

Summary: We describe how to compile and use Java in the Grinnell College Mathematics Local Area Network (MathLAN).

Prerequisites: Unix basics. Java basics. Java packages.

Disclaimer: Although I use the term Unix throughout this document, the ideas apply equally well to Linux, the variant of Unix we use in MathLAN.

Contents:

• Files
• Compilation
• Running Your Program

Files

For the purposes of these exercises, you will find it most convenient to have one class per file. (As we will soon see, if you make changes to one class, this limits the amount of extra work the computer must do to incorporate changes.) The name of the file must match the name of the class. It must also end with the suffix .java. For example, if I created a class named First, it would go in the file First.java.

Compilation

Java requires a two-step process for you to run your programs. First, you must convert all of your .java files to .class files. (The term for this conversion is compilation.) Next, you must tell Java which class is your main class. (It turns out that it is sometimes convenient to have more than one main class.)

Compilation is fairly straightforward. Make sure your present working directory is the one that contains your .java files. Then, for each file, execute the command

/opt/jdk1.5.0/bin/javac File.java

Given that the command is overly long, you may want to add an alias to your .bashrc file.

alias jc='/opt/jdk1.5.0/bin/javac'

Running Your Program

You tell Java to run the program by using the java command.

/opt/jdk1.5.0/bin/java MainClass

You must use the fully qualified name for the class. For example, if First is in package rebelsky.sample, we would refer to it as rebelsky.sample.First.

Note that you do not use the .class suffix for this command.

Again, you will find it convenient to create an alias for this command.

History

Sunday, 30 January 2005 [Samuel A. Rebelsky]

• Created.

Tuesday, 30 August 2005 [Samuel A. Rebelsky]

• Minor edits.