Admin: 1 версия

2010-06-01T05:02:27Z

1 версия

в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

Новая страница

== Use Visitor pattern to walk through file system ==



<source lang="java">
import java.io.File;
public class VisitorTester {
public static void main(String[] args) {
DirectoryNode node = new DirectoryNode(new File(".."));
node.visit(new PrintVisitor());
}
}
class PrintVisitor {
int level = 0;
public void visitFileNode(FileNode node) {
for (int i = 0; i < level; i++)
System.out.print(" ");
System.out.println(node.getFile().getName());
}
public void visitDirectoryNode(DirectoryNode node) {
for (int i = 0; i < level; i++)
System.out.print(" ");
System.out.println(node.getDirectory().getName());
level++;
for (FileSystemNode c : node.getChildren())
c.visit(this);
level--;
}
}
interface FileSystemNode {
void visit(PrintVisitor v);
}
class FileNode implements FileSystemNode {
public FileNode(File file) {
this.file = file;
}
public File getFile() {
return file;
}
public void visit(PrintVisitor v) {
v.visitFileNode(this);
}
private File file;
}
class DirectoryNode implements FileSystemNode {
public DirectoryNode(File directory) {
this.directory = directory;
}
public void visit(PrintVisitor v) {
v.visitDirectoryNode(this);
}
public File getDirectory() {
return directory;
}
public FileSystemNode[] getChildren() {
File[] files = directory.listFiles();
FileSystemNode[] children = new FileSystemNode[files.length];
for (int i = 0; i < files.length; i++) {
File f = files[i];
if (f.isDirectory())
children[i] = new DirectoryNode(f);
else
children[i] = new FileNode(f);
}
return children;
}
private File directory;
}</source>



== Visitor, a type of multiple dispatching ==



<source lang="java">
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);
}
}</source>

← Предыдущая	Версия 05:02, 1 июня 2010
(нет различий)

Java Tutorial/Design Pattern/Visitor Pattern - История изменений

Admin: 1 версия

в 17:44, 31 мая 2010