如何在具有不同键的外部 hashMap 中传递具有相同键的内部 hashMap？答案

【问题标题】：How to pass an inner hashMap with same keys inside an outer hashMap with different keys?如何在具有不同键的外部 hashMap 中传递具有相同键的内部 hashMap？
【发布时间】：2020-01-11 22:40:59
【问题描述】：

public static HashMap<String, HashMap<String,Object>> getDataDictionary() {
    // Virtual Data Creation - Simulating The 9 Fields HAR value
    HashMap<String,Object> valueFromEachOfThoseNineFields = new HashMap<String,Object>();
    HashMap<String, HashMap<String,Object>> fileNameConstrains = new HashMap<String,HashMap<String,Object>>();
    valueFromEachOfThoseNineFields.put("A", 10);
    valueFromEachOfThoseNineFields.put("B", 20);
    valueFromEachOfThoseNineFields.put("C", 30);
    valueFromEachOfThoseNineFields.put("D", 10);
    valueFromEachOfThoseNineFields.put("E", 5);
    valueFromEachOfThoseNineFields.put("F", 20);
    valueFromEachOfThoseNineFields.put("G", 1);
    valueFromEachOfThoseNineFields.put("H", 100);
    valueFromEachOfThoseNineFields.put("I", 66);
    fileNameConstrains.put("File1", valueFromEachOfThoseNineFields);
    valueFromEachOfThoseNineFields.put("A", 10);
    valueFromEachOfThoseNineFields.put("B", 50);
    valueFromEachOfThoseNineFields.put("C", 30);
    valueFromEachOfThoseNineFields.put("D", 90);
    valueFromEachOfThoseNineFields.put("E", 5);
    valueFromEachOfThoseNineFields.put("F", 20);
    valueFromEachOfThoseNineFields.put("G", 10);
    valueFromEachOfThoseNineFields.put("H", 90);
    valueFromEachOfThoseNineFields.put("I", 61);
    fileNameConstrains.put("File2", valueFromEachOfThoseNineFields);
    valueFromEachOfThoseNineFields.put("A", 10);
    valueFromEachOfThoseNineFields.put("B", 60);
    valueFromEachOfThoseNineFields.put("C", 30);
    valueFromEachOfThoseNineFields.put("D", 2);
    valueFromEachOfThoseNineFields.put("E", 13);
    valueFromEachOfThoseNineFields.put("F", 9);
    valueFromEachOfThoseNineFields.put("G", 15);
    valueFromEachOfThoseNineFields.put("H", 88);
    valueFromEachOfThoseNineFields.put("I", 69);
    fileNameConstrains.put("File3", valueFromEachOfThoseNineFields);

    return fileNameConstrains;
}

在这种情况下，我只得到最后一组，所有数据都被覆盖，谁能帮我弄清楚如何以如下格式传递数据？

{Key="File1", value={'a'=10,'b'=5}}

等等。

【问题讨论】：

fileNameConstrains 映射的所有键都指向同一个映射对象。因此，为一个键更改映射将反映在共享该对象的所有键的值中。如果不需要，您需要为每个键声明一个新映射。
您在fileNameConstrains 中添加valueFromEachOfThoseNineFields 作为值。然后您对valueFromEachOfThoseNineFields 进行更改，这会更改fileNameConstrains 内部的状态，因为它仍然是相同的HashMap。将其添加到外部映射后，您需要使用valueFromEachOfThoseNineFields = new HashMap<String,Object>(); 创建一个new HashMap。

标签： java data-structures collections

【解决方案1】：

每次您想将值存储到 valueFromEachOfThoseNineFields 并随后将 valueFromEachOfThoseNineFields 存储到 fileNameConstrains 时，都需要将新的 HashMap 实例分配给 valueFromEachOfThoseNineFields，如下所示：

import java.util.HashMap;

public class Main {

    public static void main(String[] args) {
        System.out.println(getDataDictionary());
    }

    public static HashMap<String, HashMap<String, Object>> getDataDictionary() {
        // Virtual Data Creation - Simulating The 9 Fields HAR value
        HashMap<String, Object> valueFromEachOfThoseNineFields;
        HashMap<String, HashMap<String, Object>> fileNameConstrains = new HashMap<String, HashMap<String, Object>>();

        valueFromEachOfThoseNineFields = new HashMap<String, Object>();
        valueFromEachOfThoseNineFields.put("A", 10);
        valueFromEachOfThoseNineFields.put("B", 20);
        valueFromEachOfThoseNineFields.put("C", 30);
        valueFromEachOfThoseNineFields.put("D", 10);
        valueFromEachOfThoseNineFields.put("E", 5);
        valueFromEachOfThoseNineFields.put("F", 20);
        valueFromEachOfThoseNineFields.put("G", 1);
        valueFromEachOfThoseNineFields.put("H", 100);
        valueFromEachOfThoseNineFields.put("I", 66);
        fileNameConstrains.put("File1", valueFromEachOfThoseNineFields);

        valueFromEachOfThoseNineFields = new HashMap<String, Object>();
        valueFromEachOfThoseNineFields.put("A", 10);
        valueFromEachOfThoseNineFields.put("B", 50);
        valueFromEachOfThoseNineFields.put("C", 30);
        valueFromEachOfThoseNineFields.put("D", 90);
        valueFromEachOfThoseNineFields.put("E", 5);
        valueFromEachOfThoseNineFields.put("F", 20);
        valueFromEachOfThoseNineFields.put("G", 10);
        valueFromEachOfThoseNineFields.put("H", 90);
        valueFromEachOfThoseNineFields.put("I", 61);
        fileNameConstrains.put("File2", valueFromEachOfThoseNineFields);

        valueFromEachOfThoseNineFields = new HashMap<String, Object>();
        valueFromEachOfThoseNineFields.put("A", 10);
        valueFromEachOfThoseNineFields.put("B", 60);
        valueFromEachOfThoseNineFields.put("C", 30);
        valueFromEachOfThoseNineFields.put("D", 2);
        valueFromEachOfThoseNineFields.put("E", 13);
        valueFromEachOfThoseNineFields.put("F", 9);
        valueFromEachOfThoseNineFields.put("G", 15);
        valueFromEachOfThoseNineFields.put("H", 88);
        valueFromEachOfThoseNineFields.put("I", 69);
        fileNameConstrains.put("File3", valueFromEachOfThoseNineFields);

        return fileNameConstrains;
    }
}

输出：

{File3={A=10, B=60, C=30, D=2, E=13, F=9, G=15, H=88, I=69}, File2={A=10, B=50, C=30, D=90, E=5, F=20, G=10, H=90, I=61}, File1={A=10, B=20, C=30, D=10, E=5, F=20, G=1, H=100, I=66}}

【讨论】：

【解决方案2】：

您的数据被覆盖的原因是因为您在内部映射中使用了相同的键正如文档所说，地图的密钥应该是唯一的

所以要在这里解决您的问题，您必须在每个新文件上恢复地图

HashMap<String,Object> Map1 = new HashMap<>();
    HashMap<String, HashMap<String,Object>> fileNameConstrains = new HashMap<>();
    Map1.put("A", 10);
    Map1.put("B", 20);
    fileNameConstrains.put("File1", Map1);
    Map1 = new HashMap<String,Object>();
    Map1.put("A", 10);
    Map1.put("B", 50);
    fileNameConstrains.put("File2", Map1);
    Map1 = new HashMap<String,Object>();
    Map1.put("A", 10);
    Map1.put("B", 60);
    fileNameConstrains.put("File3", Map1);

【讨论】：