当通过反射调用它时，返回Collection的方法将返回一个数组？

Question

There is a method in the Bukkit API: getOnlinePlayers() :

public static Collection<? extends Player> getOnlinePlayers()
{
  return server.getOnlinePlayers();
}

In older versions of Bukkit it returns an array of Player[] ; while in newer versions it returns a Collection<Player> .

I wanted to make it possible to have compatibility in both new and old versions, so I use reflection to invoke it:

public static Collection<Player> getOnlinePlayers(){
    Method m;
    Object obj = null;
    try
    {
        m = Bukkit.class.getMethod("getOnlinePlayers");
        obj = m.invoke(null, (Object[])null);
    }catch (...){ // omitted
        throw new RuntimeException(...); // omitted
    }

    if (obj instanceof Player[]){
        System.out.println("array"); // Used for testing
        return Arrays.asList((Player[])obj);
    }else if (obj instanceof Collection){
        System.out.println("collection"); // Used for testing
        return (Collection<Player>)obj;
    }else{
        throw new RuntimeException(...); // omitted
    }
}

Then here's the problem: When I tried this code in both new and old versions of Bukkit, it always prints "array". I am wondering why this would happen?

Answer 1

I've found out why. The reason is that I'm testing against Spigot, which is an API based on Bukkit, but has kept the method getOnlinePlayers() returning an array even after Bukkit has changed that. When I test against Bukkit, it prints out "collection".