Basic interface question

A question in "Java Tutorials", as below.

(http://java.sun.com/docs/books/tutorial/java/IandI/QandE/interfaces-answers.html)

Question 1: What methods would a class that implements the java.lang.CharSequence interface have to implement?

Answer 1: charAt, length and subSequence.

I don't understand why the toString() method is not a "have to"?

Thanks.

[390 byte] By [calvin.liua] at [2007-11-26 19:01:14]