Java顺时针打印矩阵

public ArrayList<Integer> printMatrixClockwisely(int [][]nums){
 ArrayList<Integer> list = new ArrayList<Integer>();
 int rows = nums.length;
 int cols = nums[0].length;
 if(nums == null || cols <= 0 || rows <= 0){
 return null;
 }
 int start = 0;
 while(cols > start*2 && rows > start*2){
 printMatrixInCircle(list, nums, cols, rows, start);
 ++start;
 }
 return list;
}

private void printMatrixInCircle(ArrayList<Integer> list, int[][] nums,
 int cols, int rows, int start) {
 int endX = cols - 1 - start;
 int endY = rows - 1 - start;
 
 //从左到右打印一行
 for (int i = start; i <= endX; ++i) {
 int number = nums[start][i];
 list.add(number);
 }
 //从上到下打印一列
 if(start < endY){
 for (int i = start + 1; i <= endY; ++i) {
  int number = nums[i][endX];
  list.add(number);
 }
 }
 //从右向左打印一行
 if(start < endX && start < endY){
 for (int i = endX-1; i >= start; --i) {
  int number = nums[endY][i];
  list.add(number);
 }
 }
 //从下向上打印一列
 if(start < endX && start < endY - 1){
 for (int i = endY-1; i >= start + 1; --i) {
  int number = nums[i][start];
  list.add(number);
 }
 }
}