Interfaces and Inner Classes - Absolute Java - page 747

The part in the braces is the same as the part inside the main braces of a class
definition. The closing brace is followed by a semicolon, unlike a class definition. (This
is because the entire expression will be used as a Java statement.) The beginning part,
repeated as follows, may seem strange:

new NumberCarrier()

The new is sensible enough but what is the point of NumberCarrier() ? It looks like
this is an invocation of a constructor for NumberCarrier . But, NumberCarrier is an
interface and has no constructors. The meaning of new NumberCarrier() is simply

implements NumberCarrier

So what is being said is that the anonymous class implements the NumberCarrier
interface and is defined as shown between the main braces.
Display 13.11 shows a simple demonstration with two anonymous class definitions.
For completeness, we have also repeated the definition of the NumberCarrier interface
in this display.

Display 13.11 Anonymous Classes (part 1 of 2)

This is just a toy example to
demonstrate the Java syntax
for anonymous classes.

1 public class AnonymousClassDemo
2 {
3 public static void main(String[] args)
4 {
5 NumberCarrier anObject =
6 new NumberCarrier()
7 {
8 private int number;
9 public void setNumber( int value)
10 {
11 number = value;
12 }
13 public int getNumber()
14 {
15 return number;

16 }
17 };

18 NumberCarrier anotherObject =
19 new NumberCarrier()
20 {
21 private int number;
22 public void setNumber(int value)
23 {
24 number = 2*value;
25 }

(continued)