java - 添加和删​​除 ArrayList 中设置为 hashmap 中的值的元素

Question

所以我有一个如下所示的文件:

    1st 2nd­ nth
    e1­, ­­v1, 1
    e1, v3, 2
    e1, v4, 4
    e1, v5, 7
    e2, v1, 1
    ., ­., .
    ., ­., .
    ., ­., .

我希望第一列是 HashMap 的键(e1、e2或e3)，值是一个名为“Ratings”的ArrayList，我希望第二列具有它的值(一个int)，位于数组列表的第 n 个索引内。

这是迄今为止我的完整代码:

import java.util.*;
import java.io.*;

public class Setup
{
    public static void Setup(String[] args)
    {
        String user;
        int value, location;
        //Create a Hashmap that holds a string key and an ArrayList value
        HashMap<String, ArrayList<Integer>> userRatings = new HashMap<String, ArrayList<Integer>>();
        try
        {
            BufferedReader bufferReader = new BufferedReader(new FileReader("Student list.txt")); //read from file
            String line, sentence; //declare two string variables
            String[] sData; //declare a string array (store the contents here)
            line = bufferReader.readLine(); //Read the line
            while (line != null) //While there is a line, do this:
            {
                line = bufferReader.readLine();
                sData  = line.split(", "); //Into the string array, enter individual values in the line split by the ", " characters
                int iData[] = new int[sData.length]; //Create an int array the size of the string array
                user = sData[0];
                for (int i = 0; i <sData.length; i++) //fill the int array with the int-version of the string array
                {
                    iData[i] = Integer.parseInt(sData[i]); //pass the strings as integers into the integer array
                }
                value = iData[1];
                location = iData[2];
                if(!userRatings.containsKey(user)) //The user does not have ratings.
                {
                    ArrayList<Integer> ratings = new ArrayList<Integer>();
                    //                     ratings = userRatings.get(user);
                    for (int j = 0; j < 50; j++)
                    {
                        ratings.add(j);
                    }
                    System.out.println(user + " " + userRatings.get(user));

                }
                else //The user has ratings
                {
                    userRatings.get(user).add(location,value);
                    System.out.println(user + " " + userRatings.get(user));
                }
            }
            bufferReader.close();
        }    catch (FileNotFoundException e)
        {
            System.out.println("File does not exist or could not be found.");
        }
        catch (IOException e)
        {
            System.out.println("Can't read from file");
        }
        catch (NullPointerException e)
        {
        }
    }
}

我在修改数组列表的内容时遇到问题。

总结一下:文件第一列中的每个字符串在 HashMap (userList) 中都有自己的键程序将检查它是否有该键，如果不存在，它将创建一个新的数组列表作为该键的值。arrayList 将填充 50 个索引，其中包含“0”。之后，arraylist 将从文件中添加新值，其中第二列中的整数将添加到第 n 列的相应值中。

我将如何填充数组列表，以及如何编辑它，以便如果我想在用户 e6 的第 n 个索引处添加一个新整数，我可以？

Answer 1

我认为您可以只读取第 n 个值并使用它将该值插入列表中。

例如

List<Integer> list = new ArrayList<Integer>();
//values values (0) will be inserted into the list
//after that for each value in the nth you do something as follows    
//i is the value in the nth column, if the least value for i is 1 otherwise just use i
list.add(i-1, value); 

同样为了引用使用，接口(interface)而不是实现类如下 -

Map<String, List<Integer>> userRatings = new HashMap<String, List<Integer>>();
List<Integer> ratings = new ArrayList<Integer>();

将值插入到用户 e6 的第 n 个索引中:

List<Integer> ratings = userRatings.get(user); 
if(ratings == null) { 
     ratings = new ArrayList<Integer>(); //it's not in the map yet
     //insert 50 0s here
     userRatings.put(user, ratings);
}
ratings.add(i, value); //i is the nth index and value is the rating