Java: Implement flipLetttersInSubstring.

void flipLetttersInSubstring(int startPosition, int endPosition);

/** * Reverses the position of all letters (i.e. a-z and A-Z) in the current string, between startPosition and endPosition (both inclusive). * The first letter will become the last, and the last will become the first. All other characters remain unchanged. * *Note: The first character in the string is considered to be in Position 1. * * Examples: * - String "Rat" would be converted to "taR" * - String "3 Cats, 2 Dogs." would be converted to "3 sgoD, 2 staC." * * @param startPosition Position of the first character to consider * @param endPosition Position of the last character to consider * @throws NullPointerException If the current string is null * @throws MyIndexOutOfBoundsException If endPosition is > the length of the string or startPosition <= 0 * (and the current string is not null) * @throws IllegalArgumentException If startPosition > endPosition * (and the current string is not null, and neither position is out of bounds) */