Interfaces and Nested Classes - Multimedia Introduction to Programming Using Java - page 353

private. This is because In is defined in and is part of class Out .
4. If method meth is non-static, class In can reference all the non-static
components of class Out even if they are private. This is because In is
defined in and is part of class Out .
5. Inner class In may extend another class and implement interfaces. In
may be extended by another class.

6. Just as local variable local1 cannot be accessed outside of method meth ,
class In cannot be accessed directly outside method meth .

12.4.5 Anonymous classes

We now describe the last kind of class, the anonymous class . An anonymous
class is a class that does not have a name. That may sound kind of silly until you
stop and think about it. Why does something have a name? Because it will be
called by that name, usually many times. If something is never called or referred
to, there is no need to give it a name. Moreover, in Java, if a class is called just
once, there is a way to write it so that the name is not necessary even then.
Consider class Out , of Fig. 12.21, which contains method revIt . Local
inner class ItOver is accessed in only one place, in the return statement.
Therefore, it is a candidate for becoming an anonymous class. In Fig. 12.23, to
describe most easily how to make ItOver into an anonymous class, we show the
class with its body replaced by < body of class >.
To make ItOver into an anonymous class (see Fig. 12.24), do the following:
1. Replace the expression after new by “ Iterator() < body of class >”. Note
that there is no semicolon after < body of class > (because it ends in a
brace).

Activity
12-7.2

2. Remove the definition of class ItOver .
We now have an unnamed class, which implements Iterator .

When to use an anonymous class
Consider using an anonymous class when a class is accessed only once. But
use anonymous classes sparingly, perhaps only when the body of the class con-
tains one or two methods, because the syntax is difficult to follow. The body of

public class Out {
void meth( final int p1, int p2) {
final int local1= p2;
int local2;
public class In { … }

}

Figure 12.22: A local class, used to explain the rules of local classes