Date: 2012aug26 Updated: 2024nov28 Level: beginner Language: mixed Q. Java: the basic Java commands / tutorial A. Install On Red Hat/Fedora/CentOS install with this command:

dnf install java java-devel

That will install

java-NN-openjdk java-NN-openjdk-devel

Where NN is the latest. Simple Program Lets make a simple program in file Hello.java:

public class Hello { public static void main(String []args) { System.out.println("Hello world"); } }

The convention is to begin classes with Uppercase and to make the filename match the class name. Compile and Run Now we can compile and run it with one commmand:

java Hello.java

Displays:

Hello world

Class Files But usually we want to make .class files:

javac Hello.java - compile source .java into .class file

You can run the .class file with:

java Hello - run .class file (omit ".class")

Displays:

Hello world

Jar Files .jar files are archives that hold multiple .class files To put our Hello.class into a jar:

jar --create --main-class=Hello --file hello.jar Hello.class

Run it with:

java -jar hello.jar

Displays:

Hello world

Now, you're well on your way!