注释改了一点错误 import java.util.ArrayList; public class Solution {     public ArrayList<Integer> printMatrix(int [][] matrix) {         ArrayList<Integer> list = new ArrayList<>();         if(matrix == null || matrix.length == 0 || matrix[0].length == 0){             return list;         }         int up = 0;         int down = matrix.length-1;         int left = 0;         int right = matrix[0].length-1;         while(true){             // 最上面一行             for(int col=left;col<=right;col++){                 list.add(matrix[up][col]);             }             // 向下逼近             up++;             // 判断是否越界             if(up > down){                 break;             }             // 最右边一列             for(int row=up;row<=down;row++){                 list.add(matrix[row][right]);             }             // 向左逼近             right--;             // 判断是否越界             if(left > right){                 break;             }             // 最下面一行             for(int col=right;col>=left;col--){                 list.add(matrix[down][col]);             }             // 向上逼近             down--;             // 判断是否越界             if(up > down){                 break;             }             // 最左边一列             for(int row=down;row>=up;row--){                 list.add(matrix[row][left]);             }             // 向右逼近             left++;             // 判断是否越界             if(left > right){                 break;             }         }         return list;     } }