There is one exception to the import rule. All classes in the
java.lang package are imported by default. Thus you do
not need to import java.lang.*; to use them without
fully qualified names.
Consider the System.out.println() method we've been
using since the first day of class.
System is really the java.lang.System
class. This class has a public static field called
out which is an instance of the
java.io.PrintStream class. So when you write
System.out.println(), you're really calling the
println() method of the out field of the
java.lang.System class.