123456所有排列组合

  String str = "123456";  char[] arr1 = str.toCharArray();  char[] arr2 = Arrays.copyOf(arr1,arr1.length);  for(int i=0;i<arr1.length-1;i++){     for(int j = i+1;j<arr2.length;j++){          System.out.println(arr1[i] + "," + arr2[j]);     }  }