CS1322 - Spring 2004 - Getting Started

Introduction

Using separate components

Integrated Development Environments

Classpath Problems

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Getting Started with Java in CS 1322

Introduction
Using separate components
Integrated Development Environments
Classpath Problems

Introduction

Before you can start writing programs you need two things, a text editor and a java compiler. There are two ways to fufill these requirements, using separate components or using an integrated development environment (IDE). A text editor allows us to enter the program in human-readable form using the syntax of the Java programming language. A compiler takes the human-readable Java program and translates it into a form that can be executed by the Java Virtual Machine (JVM).

The first lecture and the first recitation will make these relationships more clear. We will also demonstate both command-line and IDE development at the first recitation.

A good place to learn about java is the Java tutorial at http://java.sun.com/docs/books/tutorial/index.html.

References to the Java classes are available on-line at http://java.sun.com/j2se/1.4.2/docs/api/

Using separate components

Using a separate compiler and editor allows you to minimize the disk space required and allows you to use your favorite text editor to do your programming (like emacs or notepad). A big disadvantage is that this limits your debugging options. Also from a future job perspective, no commercial developers generally develop this way. Almost all software development companies use IDE's to develop non-trivial applications. Developing with a separate compiler and editor is often called command-line development.

The first thing you will need to do is to download and install the java development kit, standard edition (J2SE JDK). You can get the JDK from two places:
1. The CD in the back of the book. The book provides you with J2SE version 1.4.0. This should be adequate for CS1322. The latest version is 1.4.2. If you desire to use the latest version of the JDK, would need to use option 2.
IMPORTANT: The CD contains only a windows version of the JDK. If you use a Mac, or U**x environment, you will need to use option 2.

Control Panel

System

Advanced

Environment Variables

java -version

javac my-program-name.java

java my-program-name

2. Downloading the latest version direct from sun.

java.sun.com

J2SE 1.4.2 SDK

Integrated Development Environments (IDE)

IDE's are a powerful and easy way to develop software applications. IDE's will integrate the editor, compiler and runtime functionality all into one program. The editors tend to have many helpful features like color-coded syntax highlighting, and sophisticated error checking. There are many IDE's available for Java, and the ultimate selection is often a matter of personal preference. We will cover four of the more common IDE's here.

JGRASP

JGrasp is available on the cdrom accompaning your textbook. A more up to date version is available from the JGrasp home page. The most recent version is 1.6.4. Clicking on the download link will allow you to download the latest version of the program and the available documentation. There is a pdf manual available that will give you detailed instructions on this application.

JGrasp is a fairly simple IDE. It provides basic debug and editor functionality. This is probably the best IDE to use if you are not a CS major and do not intend to ever develop larger-scale programs than those in CS1322. If you are a CS major, or you intend to develop software commercially, then one of the other more powerful IDE's would be well worth your effort to learn.

NetBeans

NetBeans is the IDE provided by Sun (The makers of java). NetBeans is a much more sophisticated IDE than JGrasp. NetBeans has a graphical GUI builder, which can help during more advanced programming assignments. You can download the latest version of NetBeans by going to the Java SDK download page and selecting the Download NetBeans IDE v 3.5.1 with J2SE v 1.4.2 COBUNDLE (info) option.

Eclipse

Eclipse is a major open-source effort to develop an extensible workspace for many different kinds of applications. Developers extend eclipse by building plug-ins. The basic download of the Eclipse IDE includes the Java development tools necessary to build java applications. Eclipse does not currently have a graphical GUI builder, but it is very competitive with its commercial counterparts. Eclipse can be downloaded from here. This is one of the best IDE's for students with Mac's. Download the latest stable version 2.1.2.

JBuilder

This is one of our instructor's (Bob) personal favorites, but it is only available for Windows, Linux or Solaris. The current version is Version 9. It has many syntax correcting help functions, plus powerful project management capabilities. JBuilder also integrates with many 3d party Java tools that will be useful in your future software development career. It has a little bit of a learning curve because it is so powerful, so if you are a casual developer, you might steer clear of this package. If however, you plan to develop professional applications, then this IDE will do it all. You want to download the free Personal version. JBuilder is available here. You do have to register with Borland to download this product, so if you have an aversion to this, you may want to consider Eclipse.

Classpath problems

One of the more frustrating things that you have to deal with in the development of Java programs is the concept of a classpath. When we create .class files from our .java text files, the java environment needs to know how to find them. That is the purpose of the classpath. It may seem stupid if we are only creating a java program that uses all the class files in a single directory to have to fool with a classpath variable. Think about building real applications though. We might need to reuse classes and libraries that other people have already developed. We need to be able to tell the compiler and the execution environment where to find those classes.

There are two different ways to set the classpath. If you use 3d party libraries in most of your projects, you can set the classpath globally through the use of environment variables. For windows we would use:
set CLASSPATH=c:\myclasses\myclasses.jar
For unix we would put the following in the .bashrc config file:
CLASSPATH=/usr/j2ee/j2ee.jar:.;export CLASSPATH

If we need to set different paths for different projects that we create, then we can pass the classpath to the compiler and the execution environment.
For the compiler we would use:
WINDOWS
javac -classpath "c:\myclasses\myclasses.jar;." my-java-prog.java
UNIX
javac -classpath "./myclasses/myclasses.jar:." my-java-prog.java

Two important things to note:
1. The primary difference between Windows and Unix in the classpath is the delimeter between locations. For windows it is a semicolon ";" and for unix it is a colon ":".
2. Note the period "." as the last entry in the classpath list. That tells Java to search the current directory for class files.

The main symptoms of a classpath problem are error messages that state
Java cannot find the startup code of your application: Exception in thread "main" java.lang.NoClassDefFoundError: foo

You reference a class in one file from another and you know that class is defined, but you still get a error like:
Demo.java:4: cannot resolve symbol symbol : class MyClass location: class Demo MyClass mc = new MyClass();

Questions? - Comments? - Suggestions?