java - 使用可比排序

Question

简介

我使用 Comparable 进行自定义排序的代码无法按照我想要的方式工作。我基本上采用目录数组并对它们进行排序:

1. 第一个目录数，越少的在先。
2. 如果按字母顺序是平局。

问题

您的输入示例:

["/", "/usr/", "/usr/local/", "/usr/local/bin/", "/games/", "/games/snake/", "/homework/", "/temp/downloads/" ]

应该返回这个:

["/", "/games/", "/homework/", "/usr/", "/games/snake/", "/temp/downloads/", "/usr/local/", "/usr/local/bin/" ]

但由于某种原因，我的代码返回以下内容:

["/", "/usr/", "/games/", "/homework/", "/usr/local/", "/games/snake/", "/usr/local/bin/", "/temp/downloads/" ]

我的代码 [已编辑评论]

import java.util.*;

public class Dirsort { public String[] sort(String[] dirs) {
    //Creates Array list containing Sort object
    ArrayList<Sort> mySort = new ArrayList<Sort>();
    //Loop that gets the 3 needed values for sorting
        for (String d: dirs){
            String [] l = d.split("/");//String array for alphabetical comparison
            int di = d.length();//Length of array for sorting by number of directories
            mySort.add(new Sort(di,l,d));//adds Sort object to arraylist (note d (the entire directory) is needed for the toString)
        }
        Collections.sort(mySort);//sorts according to compareTo
        String [] ans = new String [mySort.size()];//Creates a new string array that will be returned
        int count = 0;//to keep track of where we are in the loop for appending
        for (Sort s: mySort){
            ans[count] = s.toString();
            count++;
        }
        return ans;
    }
    class Sort implements Comparable<Sort>{
        private int d;//number of directories
        private String [] arr;//array of strings of names of directories
        private String dir;//full directory as string for toString

        //Constructor
        public Sort(int myD, String [] myArr, String myDir){
            d = myD;
            arr = myArr;
            dir = myDir;
        }

        //toString
        public String toString(){
            return dir;
        }

        @Override
        public int compareTo(Sort arg0) {
            // TODO Auto-generated method stub
            //If they are the same return 0
            if (this.equals(arg0)){
                return 0;
            }

            //if the directories are empty
            if("/".equals(arg0.dir)){
                return 1;
            }
            if ("/".equals(this.dir)){
                return -1;
            }

            //If they are not the same length the shorter one comes first
            if (this.d != arg0.d){
                return this.d - arg0.d;
            }

            //If they are the same length, compare them alphabetically
            else{
                for (int i = 0; i < arg0.d; i++){
                    if (!this.arr[i].equals(arg0.arr[i])){
                        return this.arr[i].compareTo(arg0.arr[i]);
                    }
                }
            }
            return 0;
        }   
    }
}

Answer 1

错误在这里:

for (String d: dirs){
    String [] l = d.split("/");

    int di = d.length(); // <- here

    mySort.add(new Sort(di,l,d));
}

因为您正在比较整个目录字符串的长度，而不是目录中“文件夹”的数量。这就是为什么 "/usr/" 出现在 "/homework/" 之前，例如，因为:

"/usr/".length() == 5
"/homework/".length() == 10

我相信你想要的是这个，使用分割的长度:

int di = l.length;

那么输出是:

//games//homework//usr//games/snake//temp/downloads//usr/local//usr/local/bin/

There's another small bug though (possibly), which is that calling split on a String that starts with the delimiter will result in an empty String at the beginning.

IE:

"/usr/".split("/") == { "", "usr" }

所以你可能想对此做点什么。虽然在这里这意味着它们都以空字符串开头，所以它最终不会影响您进行比较的方式。

顺便说一句，@JBNizet 的建议也是正确的，为变量提供更有意义的名称在这里会有很大帮助。 fullDir.length() 和 splitDir.length 会让这种情况更容易被发现(而且它可能从一开始就从未发生过)。