本文介绍了无法强制转换为java.lang.compable的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
虽然已经问过此问题,但我对具体实现有疑问。
我正在尝试打印二叉树的顶视图,以下是它的完整代码:
import java.util.*;
class Node{
int data;
Node right;
Node left;
Node(int data){
this.data = data;
}
}
class Pair<F,S>{
private F first;
private S second;
public Pair(F first, S second){
this.first = first;
this.second = second;
}
public F getFirst(){return first;}
public S getSecond(){return second;}
}
class BinaryTreeTopView{
public static void printTopView(Node root){
if(root == null)
return;
Queue <Pair<Node,Integer>> q = new Queue<>();
Map <Integer,Node> map = new HashMap<>();
Pair<Node,Integer> p = new Pair<>(root, 0);
q.add(p);
/*
I am storing nodes and the corresponding horizontal distances
in the form of a pair which then are being stored in the queue
to ensure level order traversal
*/
while(!q.isEmpty()){
Pair<Node,Integer> temp = q.peek();
q.remove();
if(map.containsKey(temp.getSecond())==true){
map.put(temp.getSecond(),temp.getFirst());
} else {
System.out.println(temp.getFirst().data);
map.put(temp.getSecond(),temp.getFirst());
}
if(temp.getFirst().left!=null){
Pair<Node,Integer> left = new Pair<>(temp.getFirst().left, temp.getSecond()-1);
q.add(left);
}
if(temp.getFirst().right!=null){
Pair<Node,Integer> right = new Pair<> (temp.getFirst().right, temp.getSecond()+1);
q.add(right);
}
}
}
public static void main(String[] args) {
Node root = new Node(1);
root.left = new Node(2);
root.right = new Node(3);
root.left.right = new Node(5);
root.left.left = new Node(4);
root.right.left = new Node(6);
root.right.right = new Node(7);
root.right.left.right = new Node(8);
root.right.right.left = new Node(10);
root.right.right.right = new Node(9);
root.right.right.left.right = new Node(11);
root.right.right.left.right.right = new Node(12);
printTopView(root);
}
}
它编译得很好,但是在运行时引发了异常。现在我一直收到以下异常,但我找不出问题是什么:
Exception in thread "main" java.lang.ClassCastException:
Pair cannot be cast to java.lang.Comparable at java.util.PriorityQueue.siftUpComparable(PriorityQueue.java:652)
at java.util.PriorityQueue.siftUp(PriorityQueue.java:647)
at java.util.PriorityQueue.offer(PriorityQueue.java:344)
at java.util.PriorityQueue.add(PriorityQueue.java:321)
推荐答案
这是因为Pair没有实现可比较。或者实现它:
public class Pair implements Comparable<Pair> {
public int compareTo(Pair o) {
// ...
}
}
或在优先级队列中使用比较器
使用比较器;
PriorityQueue<DummyObject> pq = new
PriorityQueue<DummyObject>(5, new DummyObjectComparator());
定义您的比较器:
class DummyObjectComparator implements Comparator<DummyObject>{
// Overriding compare()method of Comparator
public int compare(DummyObject s1, DummyObject s2) {
//some code
}
}
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