java n*n的二维数组转置，不开辟新的空间

public class RotateImage {    public static void rotate(int[][] matrix) {        if(matrix==null||matrix.length==0)            return;        int i,j;        int len=matrix.length;        for (i=0;i<len;i++)        {            for(j=0;j<len;j++)            {                if(i<j) {                    int temp = matrix[i][j];                    matrix[i][j] = matrix[j][i];                    matrix[j][i] = temp;                }            }        }        for (i=0;i<len;i++)        {            for(j=0;j<len;j++)            {                System.out.print(matrix[i][j]+" ");            }            System.out.println();        }    }    public static void main(String[] args){        int [][] matrix={{1,2,3},{4,5,6},{7,8,9}};        RotateImage.rotate(matrix);    }}