Foursquare cipher


        Boxtygit here, I have just joined this forum and git-hub in general this evening.

Now to get down to business, i am working on a four square cipher java project and i had a look at this code, it looks and seems great but at the start, the command import aca.util.Pair it will not work in my machine it throws a warning such as cannot “resolve pair to a type” and as a result it will not proceed with  the program i would  so like to see in operation as it would benefit me greatly in my OO java project.

The code above for the foursquare cipher has a problem with pair in my eclipse ide enviromnent.

what is the issue ?