Netflix phone interview questions

1, find the first repeat character in a Array.  For example, "JHIALI", then return I

2, return the most repeatable character in a Array, For example, "abcbebf", then it return b

3, 讲一下JAVA里的abstract class

4, 讲一下JAVA里的garbage collection

5, what is the different between "overriding" and "overloading"

6, swap two variable with space limitation(不允许第三个变量的出现)

7, what is ^ means(异或)