1- Create a Helloworld.java file and edit it:
   $ nano Helloworld.java
   (you may use any other text editor)

2- Enter this code:

   public class Helloworld {
        public static void main(String[] arg) {
                System.out.println("Hello World!");
        }
   }

3- Write the file and quit nano.

4- Compile it:
   $ javac Helloworld.java

5- Run it:
   $ java -cp . Helloworld
   Expected Output:
       Hello World!