如何在二维数组中返回不同的列？

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

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

        List<int[]> result = getDistinctColumns(matrix);
        for (int[] column : result) {
            for (int num : column) {
                System.out.print(num + " ");
            }
            System.out.println();
        }
    }

    public static List<int[]> getDistinctColumns(int[][] matrix) {
        List<int[]> result = new ArrayList<>();
        Set<Integer> columnSet = new HashSet<>();

        int rows = matrix.length;
        int cols = matrix[0].length;

        for (int j = 0; j < cols; j++) {
            columnSet.clear();
            int[] column = new int[rows];
            for (int i = 0; i < rows; i++) {
                column[i] = matrix[i][j];
                columnSet.add(matrix[i][j]);
            }
            if (columnSet.size() == rows) {
                result.add(column);
            }
        }

        return result;
    }
}

1 4 7 
2 5 8 
3 6 9