I' trying to find out how do you know how many characters are in a string. Because to use getChars you have to know before hand how many characters you want to end at.
Don't forget a method to get the char at a specific position. However, what you should never forget are two cases: a) the string is empty (i.e. there is no last character), and b) the string reference is null (i.e. there is no string at all).