I am not a Java programmer nor do I aspire to become one. However, sometimes I am compelled to help short people with Minecraft problems and other annoyances.

This is a very good article outlining the main ideas of Java as a concept.

What Kind Of Java Do I Have?

This command will tell you a lot.

java -XshowSettings:properties -version

I still found it tricky to know if I had Java 7 or 8 or whatever.

Installing on Ubuntu

And maybe Debian?

Let’s say you need "Java 8" because someone told you that’s what you need. This worked for me.

sudo apt install openjdk-8-jdk

Apparently just doing apt install java gets you Java 10 these days (2018-10-02).

Installing On CentOS/Red Hat

This web page seems to cover the topic well. It seems to have worked for me installing Oracle Java 8 JRE on CentOS 6 in 2016.

Hello World

When I tried Java in the 1990s it was horrific and getting even the simplest thing to happen, especially on Linux, was an ordeal. But today it seems pretty well behaved.

:-> [host][/tmp]$ cat HW.java
class HW {
    public static void main(String[] args)
    { System.out.println("Hello, world!"); }
:-> [host][/tmp]$ javac HW.java
:-> [host][/tmp]$ time java HW
Hello, world!
real    0m0.298s


Sometimes you want to make jar files like you mean it. The Debian package fastjar gets you /usr/bin/jar. Remember, jar files are just zip files with a different name and some conventions about what files are contained therein.

Very often someone just wants you to "run" a Java program. You get a jar file and then what? Something like this.

java -jar minecraft.jar