Question

所以我有一个程序可以测量用户的降雨量，并在一个只有基本的set / get mutators和accessors的Class RainFall的帮助下将它存储到一个数组中。我的问题是由于某种原因，程序在Arrays.sort（）行崩溃。是否需要为该行创建一个新方法？如果是这样的话会是什么样子？

import java.util.Arrays;
import java.util.Scanner;
public class Lab7rain {

  public static void main(String[] args) {
    double amount=0;//VARIABLE DECLARATIONS
    RainFall r = new RainFall(amount);//CREATE OBJECT
    Scanner kb = new Scanner(System.in);//ALLOCATE SPACE
    RainFall[] month = new RainFall[12];

    for(int i=0; i<12; i++){
     System.out.println("What was the amount of rain in "+r.date()+"?");//rain per month
     amount = kb.nextDouble();//gets input
     month[i]= new RainFall(amount); //stores amount into array slot
     System.out.println();
     r.setTotal(amount);//sends amount to method that adds them together to create a total
    } 

    kb.close();

    r.setAvg();//initiates method that divides total by 12 to get average rain fall per month

    System.out.println(r.getTotal());//print total rain fall
    System.out.println(r.getAvg());//print average rain fall
    System.out.println();//skip line

    Arrays.sort(month);//i want this to sort the array so i can
    //then print out the highest and lowest months
    System.out.println(month[0]+" "+month[11]);
  }
}

线程中的异常＆＃34; main＆＃34; java.lang.ClassCastException：lab7rain.RainFall无法强制转换为java.lang.Comparable at java.util.ComparableTimSort.countRunAndMakeAscending（ComparableTimSort.java:290）在java.util.ComparableTimSort.sort（ComparableTimSort.java:157）在java.util.ComparableTimSort.sort（ComparableTimSort.java:146）在java.util.Arrays.sort（Arrays.java:472）在lab7rain.Lab7rain.main（Lab7rain.java:46） Java结果：1

Answer 1

根据您在评论部分中的错误，您需要先在Comparable课程上实施RainFall界面，然后才能使用Arrays.sort()方法或使用Comparator正如 @ElliotFrisch 向您展示了答案。

public class RainFall implements Comparable<RainFall> {

    double amount;
    // your code

    public int compareTo(RainFall r) {
        return Double.compare(this.amount, r.amount); 
    }

}

Answer 2

您的班级RainFall需要实施Comparable<RainFall>，或者您可以撰写Comparator<RainFall>并使用static class RainFallComparator implements Comparator<RainFall> { public int compare(RainFall a, RainFall b) { if (a.getAmount() < b.getAmount()) return -1; else if (a.getAmount() > b.getAmount()) return 1; return 0; } }来获取该Arrays.sort(month, new RainFallComparator());。例如，

{{1}}

然后

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主要的Arrays.sort（）错误

2 个答案: