Excel stored in List<Map<String,String>> - excel

Question

I am trying to read an excel sheet and save it in Java Data Structure List> list
Basically I am having a table in the excel sheet
|Name|FirstName|emp_ID|Age|
|aaaa|bbbbbbbbb|111111|40 |
|cccc|fffffffff|222222|25 |
where the keys will be
|Name|FirstName|emp_ID|Age|
my list of map should look as bellow
{Name=aaaa, FirstName=bbbbbbbbb, emp_ID=111111, Age=40}
{Name=cccc, FirstName=fffffffff, emp_ID=222222, Age=25}
but my list is storing the second map two times
{Name=cccc, FirstName=fffffffff, emp_ID=222222, Age=25}
{Name=cccc, FirstName=fffffffff, emp_ID=222222, Age=25}
any idea how to fix the issue please or any better suggestion
Thank You in advance
Here is the code That I wrote
workbook = WorkbookFactory.create(inStream);
workSheet = workbook.getSheetAt(0);
DataFormatter df = new DataFormatter();
Map<String, String> myMap = new LinkedHashMap<>();
List<Map<String, String>> list = new ArrayList<>();
row = workSheet.getRow(0);
ArrayList<String> headersName = new ArrayList<String>();
for (int j = 0; j <= row.getPhysicalNumberOfCells(); j++) {
row.getCell(j);
if ((df.formatCellValue(row.getCell(j)).isEmpty())) {
continue;
} else {
headersName.add(df.formatCellValue(row.getCell(j)));
}
}
System.out.println(headersName);
OUTER: for (Row myrow : workSheet) {
for (int i = 0; i < myrow.getLastCellNum(); i++) {
if (myrow.getRowNum() == 0) {
continue OUTER;
}
String value = df.formatCellValue(myrow.getCell(i));
myMap.put(headersName.get(i), value);
}
list.add(myMap);
}
System.out.println(list.size());
for (Map<String, String> map : list) {
System.out.println(map);
}
the print of my list
{Name=cccc, FirstName=fffffffff, emp_ID=222222, Age=25}
{Name=cccc, FirstName=fffffffff, emp_ID=222222, Age=25}

Answer 1

The issue lies in myMap.put(headersName.get(i), value). In that line, if the key already exists in the map, it overrides it. But later on, list.add(myMap) passes a reference to the same map, not a new version of it. So on the second iteration, when the line overrides the value, it overrides it on the first map already in the list. See below for a basic example of the same issue.
import java.util.*;
public class Example {
public static void main(String []args) {
Map<String, String> myMap = new LinkedHashMap<>();
List<Map<String, String>> list = new ArrayList<>();
myMap.put("abc", "123");
list.add(myMap);
System.out.println(list.get(0));
myMap.put("abc", "234");
System.out.println(myMap);
System.out.println(list.get(0));
}
}
To fix it, look into deep copies so that changing one doesn't change them all.