您应该做这样的事情。

public static String listToString(List<?> list) {
    String result = "+";
    for (int i = 0; i < list.size(); i++) {
        result += " " + list.get(i);
    }
    return result;
}

和传递名单 listToString的参数（）。您的可以的技术上延长的ArrayList （无论是与一个匿名类或具体的）和实施的toString 自己，但似乎没有必要在这里。

and pass the list in as an argument of listToString(). You can technically extend ArrayList (either with an anonymous class or a concrete one) and implement toString yourself, but that seems unnecessary here.