No te has leído la documentación al completo
http://docs.oracle.com/javase/tutori...datatypes.html Cita: Local variables are slightly different; the compiler never assigns a default value to an uninitialized local variable. If you cannot initialize your local variable where it is declared, make sure to assign it a value before you attempt to use it. Accessing an uninitialized local variable will result in a compile-time error.
Cuando es local sí es necesario inicializarla, y como dice Fuzzylog, los IDE te obligan a ello.