错误信息:Collections 类型中的 sort(List<T>) 方法不适用于参数 (ArrayList<Date>) [英] Error Message: The method sort(List&lt;T&gt;) in the type Collections is not applicable for the arguments (ArrayList&lt;Date&gt;)

问题描述

不断收到错误消息，但不知道为什么.无法获取使用 Collections.sort() 对列表进行排序的代码

Keep getting error message, but don't know why. Can't get code to sort the list using Collections.sort()

这是我所拥有的.3个java文件.

Here is what I have. 3 java files.

接口文件.

public interface Comparable<T> {
   public int compareTo(T other);
}

类文件.

public class Date implements Comparable<Date>{

private int year;
private int month;
private int day;

public Date(int month, int day, int year){   
   this.month = month;
   this.day = day;
   this.year = year;
}

public int getYear(){
   return this.year;
}

public int getMonth(){
   return this.month;
}

public int getDay(){
   return this.day;
}
public String toString(){
   return month + "/" + day + "/" + year;
}


public int compareTo(Date other){
    if (this.year!=other.year){
        return this.year-other.year;
    } else if (this.month != other.month){
        return this.month-other.month;
    } else {
        return this.day-other.day;
    }
}

}

客户端类

import java.util.*;

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

  ArrayList<Date> dates = new ArrayList<Date>();
  dates.add(new Date(4, 13, 1743)); //Jefferson
  dates.add(new Date(2, 22, 1732)); //Washington
  dates.add(new Date(3, 16, 1751)); //Madison
  dates.add(new Date(10, 30, 1735)); //Adams
  dates.add(new Date(4, 28, 1758)); //Monroe     


  System.out.println(dates);
  Collections.sort(dates);
  System.out.println("birthdays = "+dates);

}




}

我得到的错误消息是类型集合中的方法 sort(List) 不适用于参数 (ArrayList)"

The error message I get is "The method sort(List) in the type Collections is not applicable for the arguments (ArrayList)"

推荐答案

因为 Collections.sort 需要 java.lang.Comparable 而不是你的 Comparable 接口，改变你的 Date 类来实现java.lang.Comparable.

Because Collections.sort expects java.lang.Comparable and not your Comparable interface, change your Date class to implement the java.lang.Comparable.

public class Date implements java.lang.Comparable<Date>{
 ..
}

如果由于某些原因你仍然想定义你自己的 Comparable 并且你仍然想使用 Collections.sort 那么你的 Comparable 必须是 java.util.Comparable

If you still want to define your own Comparable for some reasons and you still want to use Collections.sort then the your Comparable has to be java.util.Comparable

interface Comparable<T> extends java.lang.Comparable<T> {

}

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