HashMap为所有Keys存储相同的值 [英] HashMap storing same values for all Keys

问题描述

我想为唯一坐标存储不同的值。我使用整数数组将这些值存储在HashMap中的相应坐标，但每个键映射到上次计算的值。

代码：

  import java.util。*; 
 import java.awt.Point; 
 import java.util.ArrayList; 
 import java.util.HashMap; 
 import java.util.List; 
 import java.util.Map; 
 import java.util.Map.Entry; 
 import java.util.Set; 
 
 public class Solution 
 {
 
 @SuppressWarnings（empty-statement）
 public static void main（String [] args）
 {
扫描仪输入=新扫描仪（System.in）; 
 int n = in.nextInt（）; 
 int m = in.nextInt（）; 
 
 Integer [] ar = new Integer [3]; 
 
 Map< Point，Integer []> map = new HashMap<>（）; 
 
 for（int a0 = 0; a0  
 Point p = new Point（in.nextInt（），in.nextInt（））; 
 int a = in.nextInt（）; 
 int b = in.nextInt（）; （map.containsKey（p））{
 
 if（map.get（p）[2]<（a  -  b））{
 ar [0] = a; 
 ar [1] = b; 
 ar [2] = a  -  b; 
 map.put（p，ar）; 
} 
} else {
 ar [0] = a; 
 ar [1] = b; 
 ar [2] = a  -  b; 
 map.put（p，ar）; 
} 
 
} 
 Set< Entry< Point，Integer []>> set = map.entrySet（）; 
 List< Entry< Point，Integer []>> list = new ArrayList<>（set）; （Map.Entry< Point，Integer []>条目：list）
 
 
 $ b System.out.println（entry.getKey（）+==== + Arrays.toString（entry.getValue（）））; 
 
 
 $ b} 
} 
  

输入：

<3>

0 1 1 1

1 2 2 4

2 0 1 2

结果：

java.awt.Point [x = 0，y = 1] ==== [1，2，-1]

java.awt.Point [x = 1，y = 2] ==== [1，2，-1]

java.awt.Point [x = 2，y = 0] ==== [1，2，-1]

解决方案

您只有 ar 数组的单个实例，您只需将其存储在多个键下。您需要每次创建一个新的数组实例：

  import java.awt.Point; 
 import java.util.ArrayList; 
 import java.util.Arrays; 
 import java.util.HashMap; 
 import java.util.List; 
 import java.util.Map; 
 import java.util.Map.Entry; 
 import java.util.Scanner; 
 import java.util.Set; 
 
 public class Solution {
 
 public static void main（String [] args）{
 try（Scanner in = new Scanner（System.in））{
 int n = in.nextInt（）; 
 int m = in.nextInt（）; 
 
 Map< Point，Integer []> map = new HashMap<>（）; 
 
 for（int a0 = 0; a0  
 Point p = new Point（in.nextInt（），in.nextInt（））; 
 int a = in.nextInt（）; 
 int b = in.nextInt（）; 
 //每个键的新数组
 Integer [] ar = new Integer [3]; （map.containsKey（p））{
 
 if（map.get（p）[2]<（a  -  b））{
 ar [0] = a; 
 ar [1] = b; 
 ar [2] = a  -  b; 
 map.put（p，ar）; 
} 
} else {
 ar [0] = a; 
 ar [1] = b; 
 ar [2] = a  -  b; 
 map.put（p，ar）; 
} 
 
} 
 Set< Entry< Point，Integer []>> set = map.entrySet（）; 
 List< Entry< Point，Integer []>> list = new ArrayList<>（set）; （Map.Entry< Point，Integer []>条目：列表）
 
 b 
 System.out.println（entry.getKey（）+====+ Arrays。的toString（entry.getValue（）））; 
 
 
 
 $ b code 
 $ b 
输出： 
  java.awt.Point [x = 0，y = 1] ==== [1，1，0] 
 java.awt.Point [x = 1，y = 2] ==== [2，4，-2] 
 java.awt.Point [x = 2，y = 0] === = [1，2，-1] 
  
（还要注意 n 实际上并没有在任何地方被读取。）
 
 
 
为了更好地理解这个简化的例子：
 
 
  import java.util.HashMap; 
 import java.util.Map; 
 
 public class SimpleSolution {
 
 public static void main（String [] args）{
 Map< Integer，Integer []> map = new HashMap<>（）; 
 Integer [] arr = new Integer [1]; 
 
 arr [0] = 1; 
 map.put（1，arr）; 
 System.out.println（map）; 
 System.out.println（map.get（1）[0]）; 
 arr [0] = 2; 
 map.put（2，arr）; 
 System.out.println（map）; 
 System.out.println（map.get（1）[0]）; 
 
 
 $ / code $ / pre 
 $ b $输出：
 
 
  {1 = [Ljava.lang.Integer; @ 2a139a55} 
 1 
 {1 = [Ljava.lang.Integer; @ 2a139a55， 2 = [Ljava.lang.Integer; @ 2a139a55} 
 2 
  
您可以看到这里是 
 
 
 
 
键1和2都具有相同的数组引用
 
 
设置 arr [0] 设置为2，键1的值在地图中也发生了变化
 
 
 
I want to store different values for unique coordinates.I am using integer array to store those values in HashMap to corresponding coordinates but every key maps to last calculated value.


Code :
import java.util.*;
import java.awt.Point;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

public class Solution
{

@SuppressWarnings("empty-statement")
public static void main(String[] args)
{
    Scanner in = new Scanner(System.in);
    int n = in.nextInt();
    int m = in.nextInt();

    Integer[] ar = new Integer[3];

    Map<Point, Integer[]> map = new HashMap<>();

    for (int a0 = 0; a0 < m; a0++) {

        Point p = new Point(in.nextInt(), in.nextInt());
        int a = in.nextInt();
        int b = in.nextInt();

        if (map.containsKey(p)) {

            if (map.get(p)[2] < (a - b)) {
                ar[0] = a;
                ar[1] = b;
                ar[2] = a - b;
                map.put(p, ar);
            }
        } else {
            ar[0] = a;
            ar[1] = b;
            ar[2] = a - b;
            map.put(p, ar);
        }

    }
    Set<Entry<Point, Integer[]>> set = map.entrySet();
    List<Entry<Point, Integer[]>> list = new ArrayList<>(set);


    for (Map.Entry<Point, Integer[]> entry : list)
        System.out.println(entry.getKey() + " ==== " + Arrays.toString(entry.getValue()));



}
}
Input : 

3 3

0 1 1 1

1 2 2 4

2 0 1 2

Result :

java.awt.Point[x=0,y=1] ==== [1, 2, -1]

java.awt.Point[x=1,y=2] ==== [1, 2, -1]

java.awt.Point[x=2,y=0] ==== [1, 2, -1]
解决方案
You only have one single instance of your ar array and you are just storing it under multiple keys. You need to create a new array instance each time:
import java.awt.Point;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;
import java.util.Set;

public class Solution {

    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            int n = in.nextInt();
            int m = in.nextInt();

            Map<Point, Integer[]> map = new HashMap<>();

            for (int a0 = 0; a0 < m; a0++) {

                Point p = new Point(in.nextInt(), in.nextInt());
                int a = in.nextInt();
                int b = in.nextInt();
                // New array for each key
                Integer[] ar = new Integer[3];

                if (map.containsKey(p)) {

                    if (map.get(p)[2] < (a - b)) {
                        ar[0] = a;
                        ar[1] = b;
                        ar[2] = a - b;
                        map.put(p, ar);
                    }
                } else {
                    ar[0] = a;
                    ar[1] = b;
                    ar[2] = a - b;
                    map.put(p, ar);
                }

            }
            Set<Entry<Point, Integer[]>> set = map.entrySet();
            List<Entry<Point, Integer[]>> list = new ArrayList<>(set);

            for (Map.Entry<Point, Integer[]> entry : list)
                System.out.println(entry.getKey() + " ==== " + Arrays.toString(entry.getValue()));

        }
    }
}
Output:
java.awt.Point[x=0,y=1] ==== [1, 1, 0]
java.awt.Point[x=1,y=2] ==== [2, 4, -2]
java.awt.Point[x=2,y=0] ==== [1, 2, -1]
(Also note that n isn't actually read anywhere.)

For a better understanding consider this simplified example:
import java.util.HashMap;
import java.util.Map;

public class SimpleSolution {

    public static void main(String[] args) {
        Map<Integer, Integer[]> map = new HashMap<>();
        Integer[] arr = new Integer[1];

        arr[0] = 1;
        map.put(1, arr);
        System.out.println(map);
        System.out.println(map.get(1)[0]);
        arr[0] = 2;
        map.put(2, arr);
        System.out.println(map);
        System.out.println(map.get(1)[0]);
    }
}
Output:
{1=[Ljava.lang.Integer;@2a139a55}
1
{1=[Ljava.lang.Integer;@2a139a55, 2=[Ljava.lang.Integer;@2a139a55}
2
What you can see here is

Key 1 and 2 both have the same array reference
After setting arr[0] to 2, the value for key 1 has also changed in the map


                        
这篇关于HashMap为所有Keys存储相同的值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！