Getting Started

First Steps

Install the Java Development Environment

You can get OpenJDK from https://jdk.java.net/11/. Nowaways there are only tiny difference between OpenJDK and Oracle JDK so which one you install should not matter for the most part.

Make sure that you install a relatively recent Java version (9 or newer) since some features we discuss are not available in older Java versions.

Learn how to use Java’s toolchain

The Java Development Toolkit (JDK) contains several binaries that are used to run compiled Java bytecode, to compile code, to create jar archives, a shell for interpreted execution, and several others. The first step when using Java will be to familiarize yourself with the use of these binaries. The most important ones for are now are javac the compiler that generates .class files storing java byte code and java that starts a Java Virtual Machine to execute code. Below is a very basic example:

javac takes a list of sources files (.java) and compiles them into a list of class files (.class) that contain java bytecode. Run javac -help to see a list of available options. javac is used like this:

javac [-cp <class_path>] [-d <binary_dir>] <source_files>

Here <source_files> is a list of .java files you want to compile, <class_path> is a list (elements are separated by :) of directories and jar files that contain user-defined classes that are used by the sources files you want to compile, and <binary_dir> is the directory where the generated class files will be stored.

If searching for a class, Java will search within subdirectories corresponding to the package of the class within each directory listed in the class path and within all jar files listed in the classpath. For example, if you the classpath is mylib:myotherlib/subdir and we are searching for a class mypackage.MyClass then Java will check for this class in mylib/mypackage/ and myotherlib/subdir/mypackage.

Note that jar files have to be listed individually. It is not possible to include all jar files in a directory by adding this directory to the classpath!

The java command is used to start a JVM and execute code. It is called like this:

java [-cp <class_path>] <class_name>

Here <class_path> is a class path as above and <class_name> is the fully qualified (including the package) name of the class which contains the main method you want to run.

If the class we want to execute is stored in a jar file, then you can either add the jar file to the class path or use the -jar option. Any parameters passed after <class_name> will be passed as a String[] to the main method.

Since Java versions 9, Java also comes with an interactive shell called jshell. To start jshell:

jshell

Learn how to use an IDE and/or Programmers Texteditor

Using the right tools will greatly enhance your programming experience. You want to setup a and learn how to use a good Java IDE and/or programmers text editor. Also see here. Following is a (highly biased) selection of IDEs and Editors you may want to check out:

IDEs

• Eclipse: One of the best Java IDEs (also support for many other languages can be added): https://www.eclipse.org/downloads/
• NetBeans: Has been open sourced, but not all functionality available for newer Java versions yet. Otherwise, a great IDE: https://netbeans.org/
• Or if you prefer cloud IDEs CodeEnvy: https://codenvy.io/

Editors

• Emacs: slow learning curve, but extremly powerful and extensible if you do not mind the odd keyboard shortcuts: https://www.gnu.org/software/emacs/
• Vi: very fast, low resource consumption, extremly powerful and extensible: https://www.vim.org/
• Atom: https://atom.io/
• Visual Studio code: https://code.visualstudio.com/

Learn how to use git

git is a version control system which allows you to store multiple versions of your code in a repository on your local disc. Such repositories can be syncronized with hosted copies of a repository. We will make use of two hosting services: BitBucket for labs and GitHub for all other course content. The screencast below shows how to clone the CS116 repository.

You can use git either from the commandline, through IDE or editor plugins, or using a standalone GUI.

• Installing git: https://git-scm.com/
• Git Tutorials and Implementation: official git documentation, gitmagic, Pro Git
• IDE/Editor Support: for example, Eclispe supports git as a version management system, for Emacs you can use magit
• Standalong GUIs: Sourcetree is a good one. The official git webpage has a quite extensive list: https://git-scm.com/downloads/guis

Use the excellent Java documentation

Java provides quite a lot of functionality out of the box. It is easy to get overwhelmed. Finding out what classes exist and what interface they provide is easy using Java’s online javadoc documentation: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/module-summary.html. The main documentation is here: https://docs.oracle.com/en/java/javase/11/.

Next Steps

Learn about debugging

Learn about testing

Learn how to use the shell

Outlook

Learn about build tools

• Ant
• Maven
• Gradle

Learn about Virtualization

Learn about DevOps