java如何以矩阵格式存储ArrayList，ArrayList应该是字符串数据？

Question

在这段代码中，我在ml.getV()方法中得到了错误ArrayoutofBoundException和NullPointerException

这是我的矩阵课

public class Matrix {
    private double [][] V = null;
// public members
    public static int RowsOfVMatrix = 9219;
    public static int ColsOfVMatrix = 5;
    public static int ROW_INCREASE = 20;

    public double[][] getV() {
        return V;
    }
    public void setV(double[][] v) {
        V = v;
    }
    public static int getRowsOfVMatrix() {
        return RowsOfVMatrix;
    }
    public static void setRowsOfVMatrix(int rowsOfVMatrix) {
        RowsOfVMatrix = rowsOfVMatrix;
    }
    public static int getColsOfVMatrix() {
        return ColsOfVMatrix;
    }
    public static void setColsOfVMatrix(int colsOfVMatrix) {
        ColsOfVMatrix = colsOfVMatrix;
    }
    public static int getROW_INCREASE() {
        return ROW_INCREASE;
    }
    public static void setROW_INCREASE(int rOW_INCREASE) {
        ROW_INCREASE = rOW_INCREASE;
    }
    public Matrix(){
        V = new double[Matrix.RowsOfVMatrix][Matrix.ColsOfVMatrix];
    }
    public Matrix(int rowsSize, int colSize){
        Matrix.RowsOfVMatrix = rowsSize;
        Matrix.ColsOfVMatrix = colSize;
        V = new double[Matrix.RowsOfVMatrix][Matrix.ColsOfVMatrix];
    }
    public Matrix(Matrix m){
        V = new double[Matrix.RowsOfVMatrix][Matrix.ColsOfVMatrix];
        for (int i = 0; i < Matrix.RowsOfVMatrix; i++) {
            for (int j = 0; j < Matrix.ColsOfVMatrix; j++) {
                this.V[i][j] = m.V[i][j];
            }
        }       
    }

我使用以下代码在Matrix中尝试了这个代码存储ArrayList

public static List<Matrix> readFromFileGetMatrixList(String filename)
                throws IOException {
            List<Matrix> ml = new ArrayList<Matrix>();
            Matrix m = null;
            FileReader fr = new FileReader(filename);
            BufferedReader br = new BufferedReader(fr);
            String lineContent;
            int matrixNum = 0;
            while ((lineContent = br.readLine()) != null) {
                if (lineContent.contains("#")) {
                    matrixNum++;
                }
            }
        matrixNum--;// the last one may be incomplete,so remove it from list
            br.close();
            fr.close();
            fr = new FileReader(filename);
            br = new BufferedReader(fr);
            int matrixRow_index = 0;
            int matrixCount = 0;
            while ((lineContent = br.readLine()) != null) {
                if (lineContent.contains("#")) {
                    if (matrixCount > 0) {
                        ml.add(m);
                        matrixRow_index = 0;
                    }
                    if (matrixCount == matrixNum)
                        break;
                    m = new Matrix();
                    continue;
                }
                if (lineContent.equals("")) {
                    matrixCount++;
                    continue;
                }
                String[] str = lineContent.split("\t");
                for (int j = 0; j < str.length; j++) {
                    m.getV()[matrixRow_index][j] = Double.parseDouble(str[j]); //Null pointer Exception
     }
                matrixRow_index++;
            }
            return ml;
        }

这是我的文本文件示例

0 qid:1 1:1.000000 2:0.693147 3:0.166667 #docid = 285257 0 qid:1 1:1.000000 2:0.693147 3:0.166667 #docid = 285285 0 qid:1 1:1.000000 2:0.693147 3:0.166667 #docid = 285289 0 qid:1 1:1.000000 2:0.693147 3:0.166667 #docid = 285245

在上面的代码中，我得到了ArrayBoundofIndexError