davidackroyd99/hello-world

Hello World . Learning Java and Maven - try this exercise.

hello-world

This GitHub repository contains the source code for a "Hello World" example program written in the Java programming language and project files to automate the building of the program.

For this first exercise there is no need to write any Java program text, the focus is on downloading and building your first Java application using the example source code.

Preparation

Install the necessary software.

For Windows user, Visual Studio Code and AdoptOpenJDK are recommended. See here for more information https://code.visualstudio.com/docs/languages/java or click on this link https://aka.ms/vscode-java-installer-win

If you are using a different operating system or wish to use a different IDE then you must install the following.

1. JDK (Java Development Kit)
2. Maven
3. A programmer's editor or IDE (Integrated Development Environment)
4. Git (this is optional)

See the wiki athttps://github.com/ExeterBScDTS/hello-world/wiki for information on downloading and installing these software packages.

The exercise

This first exercise does not require any programming, so no knowledge of Java is required. The purpose of the exercise is to ensure all the software required to develop Java applications is correctly installed and then guide you through the typical workflow for compiling and testing a Java program.

1. Download this repository

   As you are not going to be writing a program for this exercise it will be necessary to download an existing program and compile it from source code.

   Either download a Zip archive of this example here https://github.com/ExeterBScDTS/hello-world/archive/master.zip or make a local copy of this repository using the git program.

   Note that git can download using either the https or ssh protocol. You should use the https protocol unless you are already familiar with ssh and have the ssh software installed on your computer. If you have enabled 2-factor authentication on your GitHub account you must create a personal access token. See https://help.github.com/articles/creating-a-personal-access-token-for-the-command-line/

   You should enter these commands at the Windows command prompt (or in a shell terminal if you are using Mac or Linux)

   The REPOSITORY_URL is the text from the Clone or download button in the GitHub repository web page. If you are viewing this document on GitHub you should see this green button near the top right. Be sure to select the https version of the URL.

   mkdir java_exercises
   cd java_exercises
   git clone REPOSITORY_URL

2. Check that the Java compiler and Maven are installed

   Open VS Code and from the Terminal menu select New Terminal. You can now check if the Java compiler is correctly installed. If the commands javac and mvn are available then you have most likely got a useable build environment.

   javac -version

   Should return a message like this

   javac 1.8.0_172

   and

   mvn -version

   Should return a message like

   Apache Maven 3.5.0
   Maven home: /usr/share/maven
   Java version: 1.8.0_172, vendor: Oracle Corporation
   Java home: /usr/lib/jvm/jdk1.8.0_172-amd64/jre
   Default locale: en_GB, platform encoding: UTF-8
   OS name: "linux", version: "4.13.0-45-generic", arch: "amd64", family: "unix"

3. Compile the hello-world application

   In VS Code you can compile a project by right clicking on the Maven Project "hello-world" in the Explorer view.

   Or you can use the mvn command. First you must change directory so you are in the project directory.

   cd hello-world
   mvn compile

   If all is well this should give many lines of output most beginning [INFO] and perhaps a few beginning [WARNING].

4. Run the compiled program

   java -cp ./target/classes HelloWorld

5. Create the jar package

   mvn package

   Now you can run the program from the jarfile package, like this

   java -jar target/hello-world-0.1.0.jar

6. Now try modifying the program

   Instructions on creating a simple program from scratch

   https://code.visualstudio.com/docs/java/java-tutorial#_create-the-program