私有变量在类之外被修改 - Java

Question

I'm looping through some data, creating an ArrayList<ArrayList<Cell>> of each step. Each Cell class stores a row and col (among other things).

My problem is that when I investigate my listOfCells afterward, every Cell object has the same row (the last row of myData . This only happens with row , the columns are as they should be (that is, unique to themselves). From what I can tell, row is incrementing properly, but when it does, it changes all the values of row in my listOfCells .

I have no idea what's causing this.

Creating Cell 's

Cell cell = null;
int row = 0;
int col = 0;
ArrayList<Cell> tmpCellList = new ArrayList<Cell>();
ArrayList<ArrayList<Cell>> listOfCells = new ArrayList<ArrayList<Cell>>();    

for (ArrayList<double> eachRow : myData) {
    row++;
    for (double eachCol : eachRow) {
        col++;
        cell = new Cell();
        cell.setCol(col);
        cell.setRow(row);
        cell.setValue(eachCol);
        tmpCellList.add(cell);
    }
    listOfCells.add(row-1, tmpCellList);
 }

Cell Class

public class Cell {
    private int row;
    private int col;
    private double value;

public void setRow(int rowIn)   {
    this.row = rowIn;
}

public int getRow() {
    return row;
}

public void setCol(int colIn)   {
    this.col = colIn;
}

public int getCol() {
    return col;
}

    public void setValue(double val) {
            this.value = val;
    }

    public double getValue() {
            return value;
    }

Answer 1

All of your rows are the same ArrayList<Cell> .
Therefore, they all contain the same cells.

You need to create a new ArrayList<Cell>() for each row.