Same problem as before with your other codes. You do not know what a complex number is.
"(a + b)" is just a regular real number. It's not a complex number.
Look at my last comment here: http://question.onlinegdb.com/10571/error-complex_number-private-within-context-code-what-wrong
Java does not have any support for complex numbers. You have to write your own class. You must have a real and an imaginary part. This means at least two variables. You only have one (n). So your code will never work until you have both of the components present in your class.