Constructor dependency injection

DependencyInjection.java

public final class CustomCommandPlugin extends JavaPlugin {

    @Override
    public final void onEnable() {
        getCommand("command").setExecutor(new CommandClass(getConfig().getString("Hello-Message")));
        // creating a new instance of the command class, passing in the hello message parameter as the String from the command class' constructor.
        // getCommand being an inherited method from JavaPlugin.
        // setExecutor being a method which every PluginCommand has, defining where it will run to.
        // new CommandClass being the constructor of the class below.
        // getConfig().getString("Hello-Message"); being a String located in the config, if this string is not there:
        // IF THE STRING IS NOT THERE YOU WILL GET A NULL POINTER EXCEPTION
    }

}

public final class CommandClass implements CommandExecutor {

    private final String helloMessage;
    // declaring a field of the string hello messsage, local to this class.

    // The constructor of the "CommandClass" class, this will be called when you use "new CommandClass", and you
    // will have to provide it with parameters, in this case a string, if you have added them into the constructor.
    // String helloMessage could be changed to anything, for example you could change this to a Runnable, which you
    // could execute using Runnable#run etc.
    public CommandClass(String helloMessage) {
        this.helloMessage = helloMessage;
        // setting the helloMessage object, passed from the constructor to the local one in the class
        // this, refering to the current class, not a static, or global, variable.
        // this.helloMessage, refering to the current class' variable, named helloMessage
        // helloMessage, refering to the string passed in from the constructor.
    }

    // The method for the command, called when a player runs the command which links back to here.
    @Override//                                                 *Exerosis quirk*
    public boolean onCommand(CommandSender sender, Command command, String $, String[] args) {
        // Sending the sender a message, usign the passed in string from the constructor.
        sender.sendMessage(helloMessage);
        return true;
    }

}

System.out.println("Excellent example of Dependency Injection A+");