31 - Rotate string

Dear Eli, Hi!

First of all let me clarify: this exercise is a valuable for more "low-level" languages, which has mutable strings, like C (with char[] for string) Pascal or even Fortran. It makes less sense with immutable strings like in Java and Python. The matter is we want to perform operation without using additional memory besides the string container itself (perhaps one or two single value variables are ok).

e.g. your code (and very general) making two substrings and concatenating them is not "in-place" (we seem to create from 1 to 3 new strings depending on implementation).

Why the task called "Rotate" string while actually all that task requiring us is just simply SHIFT

But you see, some part of the string is shifted beyond the end and added from other side. That is the concept of circular buffer and we usually call this rotate rather than shift (when such part is discarded, not added anywhere).

E.g. for abcde shift 2 chars right will give abc, but rotate will give deabc. Another word for it is Circular Shift

Please advice why you suggest to REVERT the order of characters

Because if we try doing it in-place, the problem becomes difficult. Reverting twice (around different centers) is one popular approach (but there are others).

does copying the String to char array and further manipulating of array element will be concermed in term of professional the programming on Java on economic one

Let's add some concretics. Try making array of string, revert this array and make string of it again:

char[] arr = source_str.toCharArray();
...
char c;
int i, j, k;
// some manipulations on arr itself, you are only allowed to use arr, c, i, j, k variables!

String target_str = new String(arr);

This is not relevant (or is orthogonal) to "professional Java programming", as professionally we don't need to solve such problems. It's rather logic puzzle about more low-level algorithm.

it is clear for everybody I'd rather will suggest to use more correct adjective "lowercase"

Yeah, thanks, that's correct, let's change it to "lowercase". You may see I'm not guru in English, and when I started the site my English was even more poor - so there are still mistakes and flaws :)

P.S. By the way, please note that you still feel bit too relaxed about following Java Coding Style guidelines in naming variables for example! Also it would be good to separate the code of reverting string into dedicated function, for example :)