I am new to Java and could use some help.

Trying to write something using scanner or a JoptionPane to convert inputs from Gregorian to Julian. Then use interface to convert it the other way.

How do I start and what do I do?

Look at the Calendar classes for methods to do the conversions.

use interface to convert

Strange to use Scanner to get input and then use GUI for the other way???
Or did you mean something else by "interface"?

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