Java 泛型问题：类“不在类型变量的范围内”错误。

我正在开发一个涉及泛型的类项目。

public interface Keyable <T> {public String getKey();}

public interface DataElement extends Comparable<Keyable<DataElement>>, Keyable<DataElement>, Serializable {...}
public class Course implements DataElement {...}


public interface SearchTree<K extends Comparable<Keyable<K>> & Keyable<K>> extends Serializable {...}
public class MySearchTree implements SearchTree<Course> {
...
    private class Node {
        public Course data;
        public Node left;
        public Node right;
        ...
    }
}

当尝试在 MySearchTree 声明中使用 Course 类时，我收到一个类型参数错误，指出“课程不在类型变量 K 的范围内”。我花了很多时间试图找出 Course 可能缺少哪些属性而使其不符合要求，但一无所获。

有任何想法吗？

In MySearchTree the K基本类型是Course. So K必须“延长”Comparable<Keyable<Course>> & Keyable<Course>。但事实并非如此，它延伸了Comparable<Keyable<DataElement>> & Keyable<DataElement>.

I guess DataElement应该以类似的方式泛化Comparable or Enum.

public interface Keyable <T> {public String getKey();}

public interface DataElement<THIS extends DataElement<THIS>> extends Comparable<Keyable<THIS>>, Keyable<THIS>, Serializable {...}
public class Course implements DataElement<Course> {...}


public interface SearchTree<K extends Comparable<Keyable<K>> & Keyable<K>> extends Serializable {...}
public class MySearchTree implements SearchTree<Course> {