why array is not sorted in below javacode? [closed]

Answer 1

Because you don't sort the entire array. In this line:

Arrays.sort(p, 5, 9);

you are sorting the array only from the position 5 to 9. Use could use instead:

Arrays.sort(p, 0, p.length);

In this way you are sure that you are sorting the entire array from the first position (index zero) to the last position (the last parameter indicates the last exclusive index).

But it is easier to use:

Arrays.sort(p);

that automatically sort the entire array as explained above.

Answer 2

From the java docs of Arrays.sort()

The range to be sorted extends from index fromIndex, inclusive, to index toIndex, exclusive.

I think you are expecting to include index 9 as well in your sorting. In that case you need to pass p.length (that is 10) instead of 9.

Answer 3

You're specifically asking to sort the portion from p[5] to p[9] exclusive of the upper bound... so 4 elements, which are already in order (1, 4, 5, 6).

If you want to sort to p[9] inclusive, you should call

Arrays.sort(p, 5, 10);

From the documentation:

toIndex - the index of the last element, exclusive, to be sorted

Of course, that still won't sort the whole array - just the last part of it, so you'd end up with { 2, 7, 8, 3, 9, 0, 1, 4, 5, 6 }. To sort the whole array, just call Arrays.sort(p).

Note that the pattern of specifying a range using an inclusive lower bound and an exclusive upper bound is very common in computing, and you should get used to it. Another common example is String.substring:

String text = "0123456789";
String substring = text.substring(0, 5); // 01234