Visitor模式

import java.util.ArrayList;
import java.util.Collection;

interface Visitor{
 public void visitElementA(ConcreteElementA elementA);//针对具体元素A的新方法
 public void visitElementB(ConcreteElementB elementB);//针对具体元素B的新方法
}
interface Element{
 public void accept(Visitor visitor);
}
class ConcreteVisitor implements Visitor{//具体的访问者

 public void visitElementA(ConcreteElementA elementA) {
  System.out.println(elementA.getName()+" visited by ConcreteVisitor ");
  
 }
 public void visitElementB(ConcreteElementB elementB) {
  System.out.println(elementB.getName()+" visited by ConcreteVisitor ");
  
 }
}
class ConcreteElementA implements Element{//具体元素A
 private String name;
 public ConcreteElementA(String name){
  this.name=name;
 }
  
 public void accept(Visitor visitor) {//接受访问者调用它针对该元素的新方法
  visitor.visitElementA(this);
  
 }
 public String getName() {
  return name;
 }
 
 
}
class ConcreteElementB implements Element{//具体元素B
 private String name;
 public ConcreteElementB(String name){
  this.name=name;
 }
 public String getName() {
  return name;
 }
 public void accept(Visitor visitor) {//接受访问者调用它针对该元素的新方法
  visitor.visitElementB(this);
  
 }
 
}
class ObjectStructure{//对象结构即元素的集合
 private Collection<Element> collection=new ArrayList<Element>();
 public void attach(Element element){
  collection.add(element);
 }
 public void detach(Element element){
  collection.remove(element);
 }
 public void accept(Visitor visitor )
   {
     for(Element element:collection){
      element.accept(visitor);
     }
   }

}
public class Client {
 public static void main(String args[]){
  Element elementA=new ConcreteElementA("ElementA");
  Element elementB=new ConcreteElementB("ElementB");
  Visitor visitor=new ConcreteVisitor();
  
  ObjectStructure os=new ObjectStructure();
  os.attach(elementA);
  os.attach(elementB);
  os.accept(visitor);
  
  }
 
}