Android™ How to Program, Second Edition

Notes on import Declarations

Notice the import declaration in Fig. B.4 (line 4). This indicates to the compiler that the program uses class Scanner. Why do we need to import class Scanner, but not classes System, String or GradeBook? Classes System and String are in package java.lang, which is implicitly imported into every Java program, so all programs can use that package’s classes without explicitly importing them. Most other classes you’ll use in Java programs must be imported explicitly.

There’s a special relationship between classes that are compiled in the same directory on disk, like classes GradeBook and GradeBookTest. By default, such classes are considered to be in the same package—known as the default package. Classes in the same ...