Java Notes

1. Install a Java JDK

1.1. Ubuntu Install

  1. Install

    sudo apt install openjdk-11-jdk-headless

  2. Confirm

    Run
    java -version
    Sample Result
    openjdk version "11.0.16" 2022-07-19
OpenJDK Runtime Environment (build 11.0.16+8-post-Ubuntu-0ubuntu122.04)
OpenJDK 64-Bit Server VM (build 11.0.16+8-post-Ubuntu-0ubuntu122.04, mixed mode, sharing)

2. Create HelloWorld

  1. Create a package dir

    mkdir -p com/xs/app/console

  2. Create a Java source code file with the following contents:

    vi com/xs/app/console/HelloWorld.java
    package com.xs.app.console;

public class HelloWorld
{
	public static void main(String[] args) {
		System.out.print("HelloWorld Don\n");
	}
}

  3. Compile the Java source code into a class file

    javac com/xs/app/console/HelloWorld.java
    Result
    com/xs/app/console/HelloWorld.class

  4. Run the Java class file.

    java com.xs.app.console.HelloWorld
    Result
    HellowWorld Don