如何做注释，将所有该类型的类添加到列表中

Question

Ok, so i have a kind of command manager for one of my programs. Theres a abstract baceclass called Command which is, really simple

public abstract class Command {

    protected String commandheader;
    protected int requiredlevel;
    protected Random rand;
    public Command(RANK rank,String command)
    {
        commandheader = command;
        requiredlevel = rank.level;
    }
}

Then in each of the classes that inherit this, i just so some oop magic.

public class MyCommand extends Command {

    public MyCommand()
    {
        super(RANK.PLAYER,"blablabla");
    }
}

Then i also have a command helper class, which keeps each of these commands in a list so i can easily find if the command, is valid when i pass it in, aswell as get a lsit of all commands that are avalable.

public class CommandHelper {
    public enum RANK{
        PLAYER(0);
        public int level;

        private RANK(int i)
        {
            level = i;
        }
    }
    static List<Command> commandlist;

    private static void initTheCommands()
    {
        //Add the commands to the list here.
        commandlist.add(new MyCommand());
    }

    //Called by my main class
    public static void Init()
    {
        if(commandlist == null)
        {
            //Were safe to initalise the stuff brah.
            commandlist = new ArrayList<Command>();
            initTheCommands();
            for(Command cmd : commandlist)
            {
                System.out.println("Loaded command: " + cmd.commandheader);
            }
            System.out.println("[INFO] Initalised the command helper");
        }
        else
        {
            System.out.println("[INFO] Command list is already populated.");
        }
    }
}

As of right now, this system works completely fine. But it has a flaw, for each command i or the other editors add, we have to manually add it to the list, and that seems tedious and can lead to problems as we sync files. So i was wondering, is there any way i can add each command to the list without having to manually put it there? Perhaps annotate my method, or something to just add it to the list? I seen something about reflection, but i don't think that's what i want exactly although im not sure about it. Iv never used nor made annotations before so im not sure weather or not this is plausible.

Answer 1

If thats what you really want to do you can do something like this...

Declare your annotation

@Target (ElementType.TYPE)
@Retention (RetentionPolicy.RUNTIME)
public @interface CommandAnnotation {
}

Annotate your commands

@CommandAnnotation
public class MyCommand {

Then check for them something like this

...
import org.reflections.Reflections;
...
public void loadCommands() {

    Reflections reflections = new Reflections("com.my.package");
    Set<Class<?>> allClasses = reflections.getSubTypesOf(Command.class);

    for (Class<?> outerClazz : allClasses) {
        CommandAnnotation annotation = outerClazz.getAnnotation(CommandAnnotation.class);
        if (annotation == null)
            continue;