map中的value保存遇到的问题_map里面的value可以放数组吗

遇到的问题：用stream流操作 对象集合baseinfos 中 对象的属性age level workyears，用一个辅助集合helper收集数据，但是结果最终是一样的(如下图)；

在Java中，Map的value可以保存数组的引用。当将数组作为value存储在Map中时，实际上是将数组的引用作为value存储，而不是将数组的副本存储。这意味着当你修改数组时，存储在Map中的value也会发生相应的改变。

下面是一个示例代码，演示了如何将数组作为value存储在Map中：

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        // 创建一个数组
        int[] array = {1, 2, 3};

        // 创建一个Map
        Map<String, int[]> map = new HashMap<>();

        // 将数组作为value存储在Map中
        map.put("array", array);

        // 修改数组
        array[0] = 10;

        // 输出修改后的数组和Map中保存的数组值
        System.out.println("数组: " + Arrays.toString(array));
        System.out.println("Map中保存的数组值: " + Arrays.toString(map.get("array")));
    }
}
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输出结果：

数组: [10, 2, 3]
Map中保存的数组值: [10, 2, 3]
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从输出结果可以看出，当修改数组时，Map中保存的数组值也发生了相应的改变。

需要注意的是，当通过Map的value修改数组时，必须使用数组的引用来进行操作，而不是通过Map的value直接重新赋值一个新的数组。否则，对数组的修改将不会反映在Map中。

ArrayList<Baseinfo> baseinfos = (ArrayList<Baseinfo>) baseinfoMapper.selectList(null);

HashMap<String, ArrayList<String>> map = new HashMap<>();
ArrayList<String> helper = new ArrayList<>();
baseinfos.stream().forEach((item)->helper.add(item.getAge().toString()));
map.put("age",helper);
helper.clear();

baseinfos.stream().forEach((item)->helper.add(item.getLevel()));
map.put("level",helper);
helper.clear();

baseinfos.stream().forEach((item)->helper.add(item.getWorkyears()));
map.put("workYears",helper);
System.out.println(map.toString());
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JDBC Connection [HikariProxyConnection@1652214584 wrapping com.mysql.cj.jdbc.ConnectionImpl@32b95de] will not be managed by Spring
==>  Preparing: SELECT id,pid,name,age,level,collage,workyears,alltag,createtime,updatetime,isdelete FROM baseinfo
==> Parameters: 
<==    Columns: id, pid, name, age, level, collage, workyears, alltag, createtime, updatetime, isdelete
<==        Row: 1, 179, Guo Lan, 47, 4AO0Usq6TK, HokU8wB04S, LzfVBJ9iPC, FJRQCeIPSP, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 2, 247, Lok Fu Shing, 23, mZ3vLbd2WP, wOdzGk7QMw, wK5ubvtqIC, oGwX4qV8ke, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==        Row: 3, 448, Chang Yun Fat, 38, wY1THGmSey, Z9tOkFcofV, NW2Wr2HEzE, z2rmZzlEjQ, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 4, 450, Chin Wing Fat, 31, 2KyvcWUzAd, cDiekbZPpK, zuMAtpABF6, a4TChHpTX0, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 5, 881, Mark Webb, 33, aNLf9vC6B4, RRQs8MD5si, LXRYXZN87z, ZSHSWk1eeh, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 6, 262, Sugawara Eita, 39, JlJSKEBXN1, 7AkSV4O50i, Nb6DhcQ4vD, 281reUQ88R, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==        Row: 7, 938, Sugawara Ayano, 40, dH7FRyh0z0, lapYHrIGZW, tvYWvR9g0g, eLXsNmW9AH, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==        Row: 8, 509, Yam Chi Ming, 25, rBqgzLjwwp, iAHjkrrdWI, s5fLFbgxRw, Vj83RartUU, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==        Row: 9, 592, Jimmy Morales, 42, H5h4eFzfMC, KsriQCaxkS, su2OREHXoS, be4kMxitpl, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 10, 243, Richard Wood, 23, IP78QVNtpG, FjVgVXkzYQ, mz9ooqLwq3, JyidPt7BqB, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==      Total: 10
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@71b0289b]
{workYears=[LzfVBJ9iPC, wK5ubvtqIC, NW2Wr2HEzE, zuMAtpABF6, LXRYXZN87z, Nb6DhcQ4vD, tvYWvR9g0g, s5fLFbgxRw, su2OREHXoS, mz9ooqLwq3], 
level=[LzfVBJ9iPC, wK5ubvtqIC, NW2Wr2HEzE, zuMAtpABF6, LXRYXZN87z, Nb6DhcQ4vD, tvYWvR9g0g, s5fLFbgxRw, su2OREHXoS, mz9ooqLwq3], 
age=[LzfVBJ9iPC, wK5ubvtqIC, NW2Wr2HEzE, zuMAtpABF6, LXRYXZN87z, Nb6DhcQ4vD, tvYWvR9g0g, s5fLFbgxRw, su2OREHXoS, mz9ooqLwq3]}

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ArrayList<Baseinfo> baseinfos = (ArrayList<Baseinfo>) baseinfoMapper.selectList(null);

HashMap<String, ArrayList<String>> map = new HashMap<>();
ArrayList<String> helper = new ArrayList<>();
baseinfos.forEach((item)->helper.add(item.getAge().toString()));
baseinfos.stream().forEach((item)->helper.add(item.getAge().toString()));
map.put("age",helper);

ArrayList<String> helper1 = new ArrayList<>();
baseinfos.stream().forEach((item)->helper1.add(item.getLevel()));
map.put("level",helper1);

ArrayList<String> helper2 = new ArrayList<>();
baseinfos.stream().forEach((item)->helper2.add(item.getWorkyears()));
map.put("workYears",helper2);
System.out.println(map.toString());
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JDBC Connection [HikariProxyConnection@1258934723 wrapping com.mysql.cj.jdbc.ConnectionImpl@18811c42] will not be managed by Spring
==>  Preparing: SELECT id,pid,name,age,level,collage,workyears,alltag,createtime,updatetime,isdelete FROM baseinfo
==> Parameters: 
<==    Columns: id, pid, name, age, level, collage, workyears, alltag, createtime, updatetime, isdelete
<==        Row: 1, 179, Guo Lan, 47, 4AO0Usq6TK, HokU8wB04S, LzfVBJ9iPC, FJRQCeIPSP, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 2, 247, Lok Fu Shing, 23, mZ3vLbd2WP, wOdzGk7QMw, wK5ubvtqIC, oGwX4qV8ke, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==        Row: 3, 448, Chang Yun Fat, 38, wY1THGmSey, Z9tOkFcofV, NW2Wr2HEzE, z2rmZzlEjQ, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 4, 450, Chin Wing Fat, 31, 2KyvcWUzAd, cDiekbZPpK, zuMAtpABF6, a4TChHpTX0, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 5, 881, Mark Webb, 33, aNLf9vC6B4, RRQs8MD5si, LXRYXZN87z, ZSHSWk1eeh, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 6, 262, Sugawara Eita, 39, JlJSKEBXN1, 7AkSV4O50i, Nb6DhcQ4vD, 281reUQ88R, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==        Row: 7, 938, Sugawara Ayano, 40, dH7FRyh0z0, lapYHrIGZW, tvYWvR9g0g, eLXsNmW9AH, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==        Row: 8, 509, Yam Chi Ming, 25, rBqgzLjwwp, iAHjkrrdWI, s5fLFbgxRw, Vj83RartUU, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==        Row: 9, 592, Jimmy Morales, 42, H5h4eFzfMC, KsriQCaxkS, su2OREHXoS, be4kMxitpl, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 1
<==        Row: 10, 243, Richard Wood, 23, IP78QVNtpG, FjVgVXkzYQ, mz9ooqLwq3, JyidPt7BqB, 2023-06-19 17:22:50, 2023-06-19 17:22:50, 0
<==      Total: 10
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@ae3c140]
{workYears=[LzfVBJ9iPC, wK5ubvtqIC, NW2Wr2HEzE, zuMAtpABF6, LXRYXZN87z, Nb6DhcQ4vD, tvYWvR9g0g, s5fLFbgxRw, su2OREHXoS, mz9ooqLwq3], 
level=[4AO0Usq6TK, mZ3vLbd2WP, wY1THGmSey, 2KyvcWUzAd, aNLf9vC6B4, JlJSKEBXN1, dH7FRyh0z0, rBqgzLjwwp, H5h4eFzfMC, IP78QVNtpG], 
age=[47, 23, 38, 31, 33, 39, 40, 25, 42, 23, 47, 23, 38, 31, 33, 39, 40, 25, 42, 23]}

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