How to fix the error: " AlphaSorter must implement the inherited abstract method java.lang.Comparable<AlphaSorter>.compareTo(AlphaSorter)?

Question

我一直在询问有关创建排序方法的问题，以对从文本文件中读取的联系人姓名链接列表进行排序，并从我之前的问题中取得进展：(What is a better method to sort strings alphabetically in a linked list that is reading in lines from a text file?)，但现在运行在使用方法 compareTo() 创建一个名为 class 的单独 class 后变成两个错误，该方法旨在覆盖我的链表 program/class 中名为 [=41] 的 sort() 方法=].

我收到两个错误：

AlphaSorter 必须实现继承的抽象方法java.lang.Comparable.compareTo(AlphaSorter)
AlphaSorter 类型的方法 compareTo(ContactNode, ContactNode) 必须覆盖或实现超类型方法

这是链表程序：ContactList.java

public class ContactList{

private ContactNode head;
private ContactNode last;
public ContactNode current;

public ContactList(){
head = null;
last = null;
current = null;}

public void addNode(ContactNode input){
if(this.head == null)
{this.head = input;
this.last = input;}
else
last.setNext(input);
input.setPrev(last);
this.last = input;}

public void traverse(){
System.out.println();
current = this.head;
while (current != null){
System.out.print(current.getName() + " ");
System.out.println("");
current = current.getNext();}
System.out.println();}

@Override
public String toString(){
ContactNode current = head;
while(current!=null){
System.out.print(current.getName() + "\n");
current = current.getNext();}
return null;}

public void insertNewFirstNode(String current){
ContactNode newNode = new ContactNode(current);
head = newNode;
if(last == null){
last = head;}}

public void sort(){
ContactList sorted = new ContactList();
ContactNode current = head
while (current != null){
if((current.getName() != null)){
current.getName().compareTo(current.getName());
sorted.insertNewFirstNode(current.getName());}
else if((current != null)){current = current.getNext();}
System.out.println(toString() + sorted);
System.out.println("");
System.out.println("");
break;}}}

这是节点 Class：ContactNode.java

public class ContactNode{
public String name;
public int index;
private ContactNode prev;
public ContactNode next;

ContactNode(String a){
this.name = a;
index = 0;
next = null;
prev = null;}

ContactNode(){}

public ContactNode getNext()
{return next;}
public ContactNode getPrev()
{return prev;}
public String getName()
{return name;}
public int getIndex(){
return index;}


public  void setNext(ContactNode newnext)
{next = newnext;}

public  void setPrev(ContactNode newprevious)
{prev = newprevious;}
public void setName(String a)
{name=a;}
public void setIndex(int b)
{index=b;}}

这是主要方法：ContactMain.java

import java.util.Scanner;
import java.io.FileReader;
import java.io.FileNotFoundException;

public class ContactMain{

public static void main(String[]args){
try{
FileReader filepath = new FileReader("data1.txt");
Scanner k = new Scanner(filepath);
ContactList myList = new ContactList();
while (k.hasNextLine()){
String i = k.nextLine();
myList.addNode(new ContactNode(i));}

myList.traverse();
System.out.println("");
myList.sort();

}catch (FileNotFoundException e){
System.out.println("File Not Found. ");}}}

最后是排序 class：AlphaSorter.java

import java.util.Comparator;
import java.io.Serializable;

class AlphaSorter implements Comparable<AlphaSorter>{
@Override
public int compareTo(ContactNode e1, ContactNode e2) {
return e1.getName().compareTo(e2.getName());}

public boolean equals(Object obj){
return this==obj;}}

我不确定 CompareTo() 方法如何与导入包一起工作。有人可以解释吗？谢谢！

Answer 1

您需要正确实施compareTo方法：

@Override
public int compareTo(ContactNode other) {
    return getName().compareTo(other.getName());
}

不要混淆 Comparable（它有一个单参数 compareTo 方法，它将当前对象与另一个对象进行比较）和 Comparator（它有一个双参数 compare 方法，并比较另外两个对象）。

Answer 2

Comparable 界面适用于那些可以将自己的 class 实例与 "natural order".

进行比较的 classes

但是，您正试图为此创建一个单独的 class。看起来您正在尝试实现 Comparator，因为您有一个 compareTo 方法来比较不同 class、ContactNode 的对象。

改为实施 Comparator<ContactNode>。

class AlphaSorter implements Comparator<ContactNode>{

此外，在 Comparator, the method is compare 中，而不是 compareTo。

@Override
public int compare(ContactNode e1, ContactNode e2) {

How to fix the error: " AlphaSorter must implement the inherited abstract method java.lang.Comparable<AlphaSorter>.compareTo(AlphaSorter)?

How to fix the error: " AlphaSorter must implement the inherited abstract method java.lang.Comparable<AlphaSorter>.compareTo(AlphaSorter)?

java

sorting

inheritance

linked-list

overriding