Java Project about returning number of unique characters

Test code, [login to view URL], and data files, [login to view URL] and [login to view URL], are provided for this assignment. The data files have had all the line feeds removed so the entire novel can be read as a single string. Write a class, [login to view URL], that has a method, getNumUniqueChars that takes a String as a parameter and returns the number of unique characters in that string. That is the number of letters that occur only once in the string. It is expected that any particular string may be passed several times to the method. Since the counting operation can be time consuming, the class should save the results, so that when the method is given a string previously encountered, it will simply retrieve the stored result. Use collections and maps where appropriate. Examples: The string "abcdefghijklmnopqrstuvwxyz" has 26 unique letters. The string "Hello Goodbye" has 5 unique letters. The string "We promptly judged antique ivory buckles for the next prize" has 15 unique letters,W m j g a q v b c k s f h x z. Extra Credit: Write a method, getNumCharsNotUnique, that does the opposite thing as getNumUniqueChars. That is, it returns the number of characters that occur more than once. The same performance criteria as above apply. Examples: The string "abcdefghijklmnopqrstuvwxyz" has 0 non-unique letters. The string "Hello Goodbye" has 3 non-unique letters. The string "We promptly judged antique ivory buckles for the next uniqueletters,e p r o t l y u d g n i.