It is because you are using anonymous inner class.
What happens is that compiler creates class for you. It calls it as your outer class and adds $ and number, e.g. $, $2 etc.
The class has reference to outer class initialized automatically, so its instance can use methods and fields of outer class.
But your class is anonymous. It kind of defined inside method and can use its internal variables defined before this anonymous class. The question is "how can it do it?" Really, you cannot refer to "instance of running method" to access its variables. The answer is that all method variables referenced from anonymous inner class are copied to the anonymous inner class . Therefore the variables are required to be final: otherwise somebody can change their values from the outer class and the changes will not be visible into the inner class.
