clover solution, i don't remember we can access to a char by charAt(), i always used it but i don't know how i forgot that. thanks for a new short way to solution.

Potential Unicode issue: if the string contains Unicode surrogate pairs (i.e. supplementary characters, like emoji and rare characters), this approach reverses those and produces a string with invalid/unintended characters. Solutions with StringBuilder#reverse() preserve the surrogate pair ordering, which is likely what you want in code.

Nice. Sometime it is better to use logic than predefined method.

WITHOUT SEMICOLON(;), is an author problem I think