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| 34. 20. 2. 访问模式，是一种多调度 |
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import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Random;
interface Visitor {
void visit(FriendsInHighSchool g);
void visit(FriendsFromNeighbour r);
void visit(NewFriends c);
}
interface Friend {
void accept(Visitor v);
}
class FriendsInHighSchool implements Friend {
public void accept(Visitor v) {
v.visit(this);
}
}
class FriendsFromNeighbour implements Friend {
public void accept(Visitor v) {
v.visit(this);
}
}
class NewFriends implements Friend {
public void accept(Visitor v) {
v.visit(this);
}
}
class Party implements Visitor {
String s;
public String toString() {
return s;
}
public void visit(FriendsInHighSchool g) {
s = "FriendsInHighSchool";
}
public void visit(FriendsFromNeighbour r) {
s = "FriendsFromNeighbour";
}
public void visit(NewFriends c) {
s = "NewFriends";
}
}
class Drink implements Visitor {
public void visit(FriendsInHighSchool g) {
System.out.println("Drink and FriendsInHighSchool");
}
public void visit(FriendsFromNeighbour r) {
System.out.println("Drink and FriendsFromNeighbour");
}
public void visit(NewFriends c) {
System.out.println("Drink and NewFriends");
}
}
class FriendsGenerator {
private static Random rand = new Random();
public static Friend newFlower() {
switch (rand.nextInt(3)) {
default:
case 0:
return new FriendsInHighSchool();
case 1:
return new FriendsFromNeighbour();
case 2:
return new NewFriends();
}
}
}
public class BeeAndFlowers {
public static void main(String args[]) {
List<Friend> flowers = new ArrayList<Friend>();
for (int i = 0; i < 10; i++)
flowers.add(FriendsGenerator.newFlower());
Party sval = new Party();
Iterator it = flowers.iterator();
while (it.hasNext()) {
((Friend) it.next()).accept(sval);
System.out.println(sval);
}
Drink bee = new Drink();
it = flowers.iterator();
while (it.hasNext())
((Friend) it.next()).accept(bee);
}
}
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