1 interface Service {
 2
 3     public void accept(Visitor visitor);
 4 }
 5
 6 class Visitor {
 7
 8     public void process(Service service) {
 9         // 基本业务
10         System.out.println("基本业务");
11     }
12
13     public void process(Saving service) {
14         // 存款
15         System.out.println("存款");
16     }
17
18     public void process(Draw service) {
19         // 提款
20         System.out.println("提款");
21     }
22
23     public void process(Fund service) {
24         System.out.println("基金");
25         // 基金
26     }
27
28 }
29
30 class Saving implements Service {
31
32     public void accept(Visitor visitor) {
33         visitor.process(this);
34
35     }
36 }
37
38 class Draw implements Service {
39
40     public void accept(Visitor visitor) {
41         visitor.process(this);
42
43     }
44 }
45
46 class Fund implements Service {
47
48     public void accept(Visitor visitor) {
49         visitor.process(this);
50
51     }
52 }

 1 // 正常逻辑实现
 2
 3         Service service1 = new Saving();
 4         Service service2 = new Fund();
 5         Service service3 = new Draw();
 6         List<Service> ls = new ArrayList<Service>();
 7         ls.add(service1);
 8         ls.add(service2);
 9         ls.add(service3);
10         for (Service service : ls) {
11             if (service instanceof Saving) {
12                 System.out.println("存款");
13             } else if (service instanceof Fund) {
14                 System.out.println("基金");
15             } else if (service instanceof Draw) {
16                 System.out.println("提款");
17             }
18         }
19         //上述的问题是随着业务量增大 代码维护量会非常的大 需要不断的去判断
20
21         //采用访问者模式解决
22         Service saving = new Saving();
23         Service fund = new Fund();
24         Service draw = new Draw();
25         Visitor visitor = new Visitor();
26         saving.accept(visitor);
27         fund.accept(visitor);
28         draw.accept(visitor);
29         //上述中accept中实际上有观察者的影子 实际上 访问者我们也可以理解成一个对业务熟悉的观察者
30         //他不断观察者是否有新的业务需求 有的话 进行相应的业务处理