Using Classes and Objects - Java Software Solutions: Foundations of Program Design - page 125

The import declaration specifies the packages and classes that will be used in a
program so that the fully qualified name is not necessary with each reference. As
we've seen, the following is an example of an import declaration:

import java.util.Scanner;

This declaration asserts that the Scanner class of the java.util package may be
used in the program. Once this import declaration is made, it is sufficient to use
the simple name Scanner when referring to that class in the program.
If two classes from two different packages have the same name, import dec-
larations will not suffice because the compiler won't be able to figure out which
class is being referenced in the flow of the code. When such situations arise, which
is rare, the fully qualified names should be used in the code.
Another form of the import declaration uses an asterisk ( * ) to indicate that any
class inside the package might be used in the program. Therefore, the following
declaration allows all classes in the java.util package to be referenced in the
program without qualifying each reference:

import java.util.*;

If only one class of a particular package will be used in a program, it is usually
better to name the class specifically in the import declaration. However, if two or
more will be used, the * notation is usually fine.
The classes of the java.lang package are automatically imported
because they are fundamental and can be thought of as basic exten-
sions to the language. Therefore, any class in the java.lang package,
such as System and String , can be used without an explicit import
declaration. It's as if all program files automatically contain the fol-
lowing declaration:

KEY CONCEPT
All classes of the java.lang pack-
age are automatically imported for
every program.

import java.lang.*;

SELF-REVIEW QUESTIONS (see answers in Appendix N)
SR 3.10 What is a Java package?
SR 3.11 What does the java.net package contain? The javax.swing package?

SR 3.12 What package contains the Scanner class? The String class? The
Random class? The Math class?
SR 3.13 Using the online Java API documentation, describe the Point class.
SR 3.14 What does an import statement accomplish?
SR 3.15 Why doesn't the String class have to be specifically imported into our
programs?