使用Comparator和Java中的对象列表

Question

我想通过键(String类型)对Type AVLNode的对象进行排序.我实例化了一个Comparator,并希望compareTo在String属性上应用Method.但是,我的IDE显示错误Cannot resolve method compareTo.我不明白为什么我不能compareTo在字符串上使用这个方法.

import java.util.*;

public class AVLTreeTest {
    public static void main(String[] args){

        Comparator<AVLNode>myComp2 = new Comparator<AVLNode>() {
            @Override public int compare(AVLNode n1, AVLNode n2) {
                return n1.getKey().compareTo(n2.getKey());
            }
        };

        AVLNode<String, AVLNode> a1 = new AVLNode( "test3", new Cuboid (2,3,4,5,6,7) );
        AVLNode<String, AVLNode> a2 = new AVLNode( "test2", new Cuboid (2,3,4,5,6,7) );
        AVLNode<String, AVLNode> a3 = new AVLNode( "test8", new Cuboid (2,3,4,5,6,7) );
        AVLNode<String, AVLNode> a4 = new AVLNode( "test1", new Cuboid (2,3,4,5,6,7) );

        List<AVLNode> listOfNodes = new ArrayList<AVLNode>();
        listOfNodes.add(a1);
        listOfNodes.add(a2);
        listOfNodes.add(a3);
        listOfNodes.add(a4);
        Collections.sort(listOfNodes, myComp2);

        for (AVLNode node : listOfNodes){
            System.out.println(node);
        }
    }
}

这是我的AVLNode类

public class AVLNode<K, V>  {

    private AVLNode<K, V> left, right, parent;
    private int height = 1;
    private K key;
    private V value;

    public AVLNode() {}
    public AVLNode(K key, V value) {
        this.key = key;
        this.value = value;
    }


    public V getValue() {
        return value;
    }

    public K getKey() {
        return key;
    }
}

我究竟做错了什么？

Answer 1

AVLNode是通用的,用K和参数化V.在你的Comparator<AVLNode>,AVLNode是生的.那是,K而且V不为人知.这意味着编译器居然不知道,如果K是Comparable.

尝试制作它Comparator<AVLNode<String, ?>>.

不相关,但也使用new AVLNode<>(...).