java矩阵有关问题

public class Matrix {    private Object[][] matrix;    private int height,width;//行，列    Matrix(){}    Matrix(int h,int w){        height=h;//矩阵行数        width=w;//矩阵列数    }    public void set(int row,int col,Object value)//将value插入row行，col列中    {        matrix=new Object[height][width];        if(row>height||row<=0||col<=0||col>width)        {            System.out.println("此项不存在!");        }        matrix[row-1][col-1]=value;    }    public Object get(int row,int col)    {        return matrix[row-1][col-1];    }    public int width(){//返回矩阵的列        return width;    }    public int height(){//返回矩阵的行        return height;    }    public Matrix add(Matrix b)//矩阵相加    {        Matrix a=new Matrix();        int i,j;        if(height!=b.height()||width!=b.width())        {            return null;        }        else        {            for(i=0;i<height;i++)            {                for(j=0;j<width;j++)                {                    String m=matrix[i][j].toString();                    String n=b.matrix[i][j].toString();                    int value=Integer.parseInt(m)+Integer.parseInt(n);                    a.set(i, j, value);                }            }            return a;        }    }    public Matrix multiply(Matrix b)    {        Matrix a=new Matrix();        if(width!=b.height())        {            return null;        }        else        {            for(int i=0;i<height;i++)            {                for(int j=0;j<b.width();j++)                {                    int value=0;                    for(int k=0;k<width;k++)                    {                        String m=matrix[i][k].toString();                        String n=b.matrix[k][j].toString();                        value+=Integer.parseInt(m)+Integer.parseInt(n);                        a.set(i+1, j+1, value);                    }                }            }            return a;        }    }    public void print() {// 打印出当前矩阵的值        if(width!=0||height!=0){            for (int i = 0; i < height; i++) {                System.out.print("|\t");                for (int j = 0; j < width; j++) {                    System.out.print(matrix[i][j] + "\t");                }                System.out.print("|\n");            }        }        else        {            System.out.println("该矩阵不存在。");        }    }    public static void main(String[] args){        Matrix a=new Matrix(2,2);        a.set(1,1,1);        a.set(1,2,2);        a.set(2,1,3);        a.set(2,2,4);        a.print();    }}