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 qualifed 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.
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