访问者模式

Posted 2021-02-12 forthedream1991

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1.基本概念

使用一个访问者类，改变元素类的执行算法，通过这种方式，元素的执行算法可以随着访问者改变而改变
目的：将数据结构与数据操作分离
应用实例：您在朋友家做客，您是访问者，朋友接受您的访问，您通过朋友的描述，然后对朋友的描述做出一个判断，这就是访问者模式。
UML

　　技术图片

2.代码实现

 1 package com.chengjie;
 2 
 3 interface ComputerPart1 {
 4     public void accept(ComputerPartVisitor computerPartVisitor);
 5 }
 6 
 7 class KeyBoard implements ComputerPart1 {
 8     @Override
 9     public void accept(ComputerPartVisitor computerPartVisitor) {
10         computerPartVisitor.visit(this);
11     }
12 }
13 
14 class Monitor  implements ComputerPart1 {
15 
16     @Override
17     public void accept(ComputerPartVisitor computerPartVisitor) {
18         computerPartVisitor.visit(this);
19     }
20 }
21 
22 class Mouse  implements ComputerPart1 {
23 
24     @Override
25     public void accept(ComputerPartVisitor computerPartVisitor) {
26         computerPartVisitor.visit(this);
27     }
28 }
29 class Computer1 implements ComputerPart1 {
30 
31     ComputerPart1[] parts;
32 
33     public Computer1(){
34         parts = new ComputerPart1[] {new Mouse(), new KeyBoard(), new Monitor()};
35     }
36 
37 
38     @Override
39     public void accept(ComputerPartVisitor computerPartVisitor) {
40         for (int i = 0; i < parts.length; i++) {
41             parts[i].accept(computerPartVisitor);
42         }
43         computerPartVisitor.visit(this);
44     }
45 }
46 
47 interface ComputerPartVisitor {
48     public void visit(Computer1 computer);
49     public void visit(Mouse mouse);
50     public void visit(KeyBoard keyboard);
51     public void visit(Monitor monitor);
52 }
53 
54 class ComputerPartDisplayVisitor implements ComputerPartVisitor {
55     @Override
56     public void visit(Computer1 computer) {
57         System.out.println("Displaying computer!");
58     }
59 
60     @Override
61     public void visit(Mouse mouse) {
62         System.out.println("Displaying Mouse.");
63     }
64 
65     @Override
66     public void visit(KeyBoard keyboard) {
67         System.out.println("Displaying Keyboard.");
68     }
69 
70     @Override
71     public void visit(Monitor monitor) {
72         System.out.println("Displaying Monitor.");
73     }
74 }
75 
76 public class TestVisitor {
77     public static void main(String[] args) {
78         Computer1 comp = new Computer1();
79         comp.accept(new ComputerPartDisplayVisitor());
80     }
81 }