Using Java to output Yang Hui triangle

This article is used to output Yang Hui triangle. The definition of Yang Hui triangle is that a certain number in it is equal to the sum of the two numbers immediately above it. The effect is as follows:

                                            1 
                                           1 1 
                                          1 2 1 
                                         1 3 3 1 
                                        1 4 6 4 1

Specific code:

public void yanghuiFun() {

        System.out.println("请输入需要打印的行数：");
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();

        if (num > 0) {
            int[][] a = new int[num][num];
            // 将每行的第一个数和最后一个数都赋为1
            for (int i = 0; i < num; i++) {
                a[i][0] = 1;
                a[i][i] = 1;
            }
            // 当行数大于2的时候就可以使用递推公式
            if (num > 2) {
                // 依次将中间某个数的值赋为其上面紧邻着的两个数的和
                for (int i = 2; i < num; i++) {
                    for (int j = 1; j < num - 1; j++) {
                        a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
                    }
                }
            }
            // 依次输出这些数
            for (int i = 0; i < num; i++) {
                // 输出数字前的空格，每行输出的空格数量为：num-1-i
                for (int j = i; j < num - 1; j++) {
                    System.out.print(" ");
                }
                // 开始输出具体的数字以及数字之间的空格
                for (int j = 0; j < i + 1; j++) {
                    System.out.print(a[i][j] + " ");
                }
                System.out.println();
            }
        }
    }