设计模式之访问者模式

访问者模式

1. 访问者模式结构图：

   

2. 示例代码：

   // 抽象访问者
   public interface Visistor {
   
       void checkWork(Engineer engineer);
   
       void checkWork(Manager manager);
   }
   
   // 具体访问者boss
   public class BossVisistor implements Visistor{
       @Override
       public void checkWork(Engineer engineer) {
           engineer.workProgress();
       }
   
       @Override
       public void checkWork(Manager manager) {
           manager.workProgress();
       }
   }
   
   // 具体访问者投资人
   public class InvestorsVisistor implements Visistor{
       @Override
       public void checkWork(Engineer engineer) {
           engineer.workProgress();
       }
   
       @Override
       public void checkWork(Manager manager) {
           manager.workProgress();
       }
   }
   
   
   // 抽象工作者（假定员工只有工程师和项目经理）
   public abstract class Worker {
       protected String name;
       abstract void accept(Visistor visistor);
   }
   
   // 具体工作者工程师
   public class Engineer extends Worker{
   
       public Engineer(String name) {
           this.name = name;
       }
   
       @Override
       void accept(Visistor visistor) {
           visistor.checkWork(this);
       }
   
       public void workProgress(){
           System.out.println(this.getClass().getSimpleName() + name + "完成工作进度：" + new Random().nextInt(100) + "%");
       }
   }
   
   // 具体工作者项目经理
   public class Manager extends Worker{
   
       public Manager(String name) {
           this.name = name;
       }
   
       @Override
       void accept(Visistor visistor) {
           visistor.checkWork(this);
       }
   
       public void workProgress(){
           System.out.println(this.getClass().getSimpleName() + name + "完成产品设计进度：" + new Random().nextInt(100) + "%");
       }
   }
   
   // 容器
   public class ObjectStruct {
       List<Worker> list = new ArrayList<>();
   
       public void accept(Visistor visistor){
           list.forEach(a -> a.accept(visistor));
       }
   
       public void add(Worker worker){
           list.add(worker);
       }
   
       public void remove(Worker worker){
           list.remove(worker);
       }
   }
   
   //　测试
   public class VisistorTest {
   
       public static void main(String[] args) {
           ObjectStruct objectStruct = new ObjectStruct();
           objectStruct.add(new Engineer("张三"));
           objectStruct.add(new Engineer("李四"));
           objectStruct.add(new Engineer("王五"));
           objectStruct.add(new Manager("斯蒂芬"));
           objectStruct.add(new Manager("詹姆斯"));
           objectStruct.add(new Manager("约翰逊"));
   
           System.out.println("=========老板检查工作进度＝＝＝＝＝＝＝＝＝＝＝");
           objectStruct.accept(new BossVisistor());
           System.out.println("=========投资人检查工作进度＝＝＝＝＝＝＝＝＝＝＝");
           objectStruct.accept(new InvestorsVisistor());
       }
   }
   
   

3. 总结：（举例不是太恰当，主要是为了学习访问者模式）

   优点：解偶数据结构与数据操作，符合单一职责原则；

   缺点：无法增加元素类型，违背依赖倒置原则．