Interfaces and Nested Classes - Multimedia Introduction to Programming Using Java - page 354

the anonymous class in this example is almost too long—that is why we replaced
the body with < body of class > when explaining the creation of the anonymous
class. In this fashion, you could see how simple it is to make a local inner class
into an anonymous class.

12.5 Key concepts

• Interface. A Java interface definition can have (in its body): (1) initializing
declarations of public static final variables and (2) declarations of public abstract
methods.

• Implementing an interface. If a class implements an interface, the class inher-
its all the components that the interface declares (or inherits from superinter-
faces). Since the inherited methods are abstract, the class must provide overrid-
ing declarations for all the inherited methods.

• An interface as a type. An interface is treated like a class-type. If a variable vc
contains the name of some class C that implements an interface I , then vc can be
cast to I , e.g. as in the assignment I vi= (I) vc; . This is a widening cast, and
such widening casts do not have to be explicitly requested. The apparent type of
variable vi is I , so that, syntactically speaking, only the components defined in
I can be referenced using vi . However, such a widening cast does not lose infor-
mation, and vi can be cast with a narrowing cast back to C , e.g. with (C) vc .
Then, all the components declared in or inherited by C can be referenced.
• Multiple inheritance. A class can implement more than one interface. In doing

public static class Out {
/** = an Iterator over b 's elements in reverse */
public static Iterator revIt( final Object[] b) {

/** a (reverse) Iterator over b */
class ItOver implements Iterator < body of class >

return new ItOver();

}

}
Figure 12.23:

Interface Iterator

public static class Out {

/** = an Iterator over b 's elements in reverse */
public static Iterator revIt( final Object[] b) {
return new Iterator() < body of class >

}

}
Figure 12.24: An anonymous class