public interface MyCustomStringInterface { /**  * Returns the current string.  * If the string is null, or has not been set to a value, it should return null.  *  * @return Current string  */  void setString(String, string); String getString();  /**  * Sets the value of the current string  *  * @param string The value to be set  */   void setString(String string); /**  * Returns the number of duplicated characters.  * This will count the number of characters that are immediately followed by another  * identical character, even if the pairs overlap.  *  * If the current string is null or empty, the method should return 0.  *  * Examples:  * - countDoubles would return 4 for string "Billy has 111 apples".  *  * @return Number of doubled characters in the current string  */  int countDuplicates(); /**  * Returns a string equivalent to the original string with n or -n added to every digit in the string.  * If 'positive' is true, n is added to every digit.  * If 'positive' is false, n is subtracted.  * The digit will wrap from 9 to 0 or 0 to 9 whenever it passes those values.  *  * Examples:  * - For n=2 and positive=true, "hello 90, bye 2" would be converted to "hello 12, bye 4".  * - For n=4 and positive=true, "1234567890" would be converted to "5678901234".  * - For n=2 and positive=false, "hello 90, bye 2" would be converted to "hello 78, bye 0".  * - For n=4 and positive=false, "1234567890" would be converted to "7890123456".  *  * @param n amount to increment or decrement every digit  * @param positive Boolean that indicates n should be treated as positive or negative  * @return String with the original string's digits incremented or decremented by n  * @throws NullPointerException If the current string is null  * @throws IllegalArgumentException If n > 9 or n <=0 (and the current string is not null)  */  String addDigits(int n, boolean positive); /**  * 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)  */  }