如何在Java中打印给定2D矩阵的所有子矩阵？

public class PrintSubMatrix {
    public static void printAllSubMatrix(int[][] matrix) {
        int rows = matrix.length;
        int cols = matrix[0].length;

        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                for (int k = i; k < rows; k++) {
                    for (int l = j; l < cols; l++) {
                        for (int m = i; m <= k; m++) {
                            for (int n = j; n <= l; n++) {
                                System.out.print(matrix[m][n] + " ");
                            }
                            System.out.println();
                        }
                        System.out.println();
                    }
                }
            }
        }
    }

    public static void main(String[] args) {
        int[][] matrix = {
            {1, 2, 3},
            {4, 5, 6},
            {7, 8, 9}
        };

        printAllSubMatrix(matrix);
    }
}