java - 重写 "Java Effective"示例中泛型方法的绑定(bind)不匹配

Question

class Main {
public static void main(String[] args) {
    List<Sub> list = new ArrayList<Sub>();

    Sub r = max(list);

    System.out.println(r);
}

static <T extends Comparable<? super T>> T max(List<? extends T> list) {
    return null;
}

private static class Super {
}

private static class Sub implements Comparable<Super> {
    public int compareTo(Super o) {
        return 0;
    }
}
}

谁能告诉我为什么在“Sub r = max(list)”行出现编译器错误？

我正在阅读 Java Effective 一书，正如他们所说，我读到了那本书中最复杂的方法声明。其实就是那个max方法。

错误是:

Bound mismatch: "The generic method max(List< ? extends T>) of type Main is not applicable for the arguments (List< Main.Sub>). The inferred type Main.Sub is not a valid substitute for the bounded parameter < T extends Comparable< ? super T>>"

Answer 1

您的 Sub 类必须扩展 Super:

private static class Sub extends Super implements Comparable<Super> {