README.md

Lesson 2: Installing Java, Compiling and Running Programs

In this lesson, we learn how to compile and run a simple Java program which just prints "Hello World!" to the console. (Lesson 01 is the introduction lesson with no examples, so we start here at 02 :-)

1. Installing Java

1.1. Under Ubuntu Linux

• open console
• type sudo apt-get update and press enter
• type in your passoword if asked to
• type sudo apt-get install openjdk-8-jdk and press enter
• type in your passoword if asked to

1.2. Under Microsoft Windows

• open browser
• go to http://www.oracle.com/technetwork/java/javase/downloads/index.html
• download the latest JDK (not the JRE!)
• after download, install

2. Verifying Installation

• open console

• type java -version

• the output should be something like:

  $ java -version openjdk version "1.8.0_121" OpenJDK Runtime Environment (build 1.8.0_121-8u121-b13-0ubuntu1.16.04.2-b13) OpenJDK 64-Bit Server VM (build 25.121-b13, mixed mode)

3. Compile and Run Programs

We use a very simple example program here, a typical Hello World! program.

Compile:

javac HelloWorld.java

you get a file HelloWorld.class which can be executed in the Java VM.

Execute (after compiling):

java HelloWorld