package visitor;
public interface IVisitor {
void visit(Element element);
}
package visitor;
public abstract class Element {
public abstract void accept(IVisitor visitor);
public abstract void doSomething();
}
package visitor;
public class Visitor implements IVisitor {
@Override
public void visit(Element element) {
// TODO Auto-generated method stub
System.out.println("對element中的數據進行操作");
element.doSomething();
}
}
package visitor;
public class ConcreteElement0 extends Element {
@Override
public void accept(IVisitor visitor) {
// TODO Auto-generated method stub
visitor.visit(this); //這是關鍵 利用雙分派技術實現處理與數據結構的分離
}
@Override
public void doSomething() {
// TODO Auto-generated method stub
System.out.println("這是元素0的方法");
}
}
package visitor;
public class ConcreteElement1 extends Element {
@Override
public void accept(IVisitor visitor) {
// TODO Auto-generated method stub
visitor.visit(this); //這是關鍵 利用雙分派技術實現處理與數據結構的分離
}
@Override
public void doSomething() {
// TODO Auto-generated method stub
System.out.println("這是元素1的方法");
}
}
package visitor;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class ObjectStruture {
public static List<Element> getList(){
List<Element> list = new ArrayList<Element>();
Random ran = new Random();
for(int i=0; i<10; i++){
int a = ran.nextInt(100);
if(a>50){
list.add(new ConcreteElement0());
}else{
list.add(new ConcreteElement1());
}
}
return list;
}
}
package visitor;
import java.util.List;
public class Client {
public static void main(String[] args) {
// TODO Auto-generated method stub
List<Element> list = ObjectStruture.getList();
for(Element e: list){
e.accept(new Visitor());
}
}
}
簡單說一下單分派和多分派:
訪問者模式的優點:
訪問者模式的適用場景:
最後還是強調一點,不要爲了用設計模式而用設計模式。當真正需要時才用,這纔是運用設計模式的正確姿勢。