Java: Issue With Storing Data from Excel in an ArrayList of ArrayLists

Question

I'm trying to store data from excel in ArrayLists, which will then be stored in a main ArrayList. The reason being that each row of the excel sheet has data that is particular to that row. I keep having an issue because I believe when I erase the inner ArrayList before looping back, it deletes the data in the master ArrayList as well.

import java.io.*;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import java.util.ArrayList;


public class StoreData {

ArrayList<ArrayList<String>> shapes;
ArrayList<String> innerMembers;
ArrayList<String> test;
int start;
int end; 

public StoreData(){
    this.shapes = new ArrayList<>();
    this.innerMembers = new ArrayList<>();
    this.test = new ArrayList<>();
    start = 0;
    end = 0;
}

public ArrayList<ArrayList<String>> storeValues(String shapeType){

    //get the shape
    switch(shapeType){
        case "A":
            start = 1;
            end = 273;
            break;
        case "B":
            start = 274;
            end = 291;
            break;
        case "C":
            start = 292;
            end = 319;
            break;
        case "D":
            start = 320;
            end = 340;
            break;
        case "E":
            start = 341;
            end = 372;
            break;
        case "F":
            start = 373;
            end = 412;
            break;
        case "G":
            start = 413;
            end = 539;
            break;
        case "H":
            start = 540;
            end = 814;
            break;
        case "I":
            start = 1464;
            end = 1958;  
    }

 try
 {
    FileInputStream x = new FileInputStream(new File("/Users/JohnDoe/Documents/File.xls"));

    //Create Workbook instance 
    Workbook workbook = new HSSFWorkbook(x);

    //Get first/desired sheet from the workbook
    Sheet sheet = workbook.getSheetAt(0);

    //Iterate through each rows one by one
    for (int i = start; i <= end; i ++){

        Row row = sheet.getRow(i++);

        //iterate through each cell in row: max number of cells is 76
        for (int j = 0; j < 77; j++) {

            Cell cell = row.getCell(j);
            cell.setCellType(1);
            innerMembers.add(cell.getStringCellValue());
    }            

    /*******************/
    //Add to master ArrayList and clear inner ArrayList to get repopulated
    /*******************/
    shapes.add(innerMembers);
    innerMembers.clear();
}
x.close();
}
catch (Exception e)
{
    e.printStackTrace();
}

/***TEST STATEMENT***/
System.out.println(shapes.get(8).get(20));
/***TEST STATEMENT***/

return shapes;

}
}

Answer 1

You might want to try:

shapes.add(new ArrayList<String>(innerMembers)); // shallow copy 
innerMembers.clear();