Design and Architectural Principles - Java 8 Lambdas - page 125

}

Our subject class is the Moon , which keeps a list of LandingObserver instances, notifies
them of landings, and can add new LandingObserver instances to spy on the Moon object
( Example 8-16 ) .

Example 8-16. Our Moon domain class—not as pretty as the real thing
public public class class Moon Moon {

private private final final List < LandingObserver > observers = new new ArrayList <>();

public public void void land ( String name ) {

for for ( LandingObserver observer : observers ) {

observer . observeLanding ( name );

}

}

public public void void startSpying ( LandingObserver observer ) {

observers . add ( observer );

}
}

We have two concrete implementations of the LandingObserver class that represent the ali-
ens' ( Example 8-17 ) and NASA's views ( Example 8-18 ) of the landing event. As mentioned
earlier, they both have different interpretations of what this situation brings them.

Example 8-17. The aliens can observe people landing on the moon
public public class class Aliens Aliens implements implements LandingObserver {

@Override
public public void void observeLanding ( String name ) {

iif ( name . contains ( "Apollo" )) {
System . out . println ( "They're distracted, lets invade earth!" );

}

}

}

Example 8-18. NASA can also observe people landing on the moon
public public class class Nasa Nasa implements implements LandingObserver {

@Override
public public void void observeLanding ( String name ) {