Given a String input str with length > 0, return an ArrayList of all the characters in the String, as single-character Strings in the order they were encountered in the original. The output must have no repeats, meaning that if a character occurs more than once in the input it will only occur once in the output, based on the first time it appears in the input.

HINT

You will need a loop for this. Also remember to declare and instantiate (and return) a new ArrayList. Also, the List interface has a handy method called contains() which can save you from having to use a nested loop. Neat!