请用java编写:计算两个同为三阶矩阵的相加、相减、相乘的结果（矩阵中的数随机产生）。

以下是Java代码：

import java.util.Random;

public class Matrix {
    private int[][] matrix;
    private int row;
    private int col;

    public Matrix(int row, int col) {
        this.row = row;
        this.col = col;
        matrix = new int[row][col];
        Random rand = new Random();
        for(int i = 0; i < row; i++) {
            for(int j = 0; j < col; j++) {
                matrix[i][j] = rand.nextInt(10); // 产生0~9之间的随机数
            }
        }
    }

    public void print() {
        for(int i = 0; i < row; i++) {
            for(int j = 0; j < col; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }

    public Matrix add(Matrix other) {
        if(this.row != other.row || this.col != other.col) {
            System.out.println("两个矩阵的行列数不相等，不能相加");
            return null;
        }
        Matrix result = new Matrix(row, col);
        for(int i = 0; i < row; i++) {
            for(int j = 0; j < col; j++) {
                result.matrix[i][j] = this.matrix[i][j] + other.matrix[i][j];
            }
        }
        return result;
    }

    public Matrix subtract(Matrix other) {
        if(this.row != other.row || this.col != other.col) {
            System.out.println("两个矩阵的行列数不相等，不能相减");
            return null;
        }
        Matrix result = new Matrix(row, col);
        for(int i = 0; i < row; i++) {
            for(int j = 0; j < col; j++) {
                result.matrix[i][j] = this.matrix[i][j] - other.matrix[i][j];
            }
        }
        return result;
    }

    public Matrix multiply(Matrix other) {
        if(this.col != other.row) {
            System.out.println("第一个矩阵的列数不等于第二个矩阵的行数，不能相乘");
            return null;
        }
        Matrix result = new Matrix(this.row, other.col);
        for(int i = 0; i < this.row; i++) {
            for(int j = 0; j < other.col; j++) {
                for(int k = 0; k < this.col; k++) {
                    result.matrix[i][j] += this.matrix[i][k] * other.matrix[k][j];
                }
            }
        }
        return result;
    }

    public static void main(String[] args) {
        Matrix a = new Matrix(3, 3);
        System.out.println("矩阵a：");
        a.print();

        Matrix b = new Matrix(3, 3);
        System.out.println("矩阵b：");
        b.print();

        Matrix c = a.add(b);
        System.out.println("矩阵a+b：");
        c.print();

        Matrix d = a.subtract(b);
        System.out.println("矩阵a-b：");
        d.print();

        Matrix e = a.multiply(b);
        System.out.println("矩阵a*b：");
        e.print();
    }
}

与前面的代码相比，这段代码没有对矩阵的行和列数进行硬编码，而是在 main 方法中创建了两个 3x3 的矩阵 a 和 b，然后计算了它们的和、差、积，并打印出来。