介绍
有限状态机通常用于模拟序列逻辑，换句话说，就是用于代表和控制执行流程。
有限状态机所需条件：
- 一个物体只有固定的几种状态（例如交通灯只有绿灯、黄灯和红灯三个状态）。
- 有固定的变化顺序（例如交通灯只能绿灯->黄灯->红灯->绿灯循环）
- 物体同一时间点上只有一种状态。
例子
这里拿一个空调做例子，图是用了别人的，这里说明下下面三个状态的意思：
off：空调关机
fanonly：空调仅吹风
cool：空调制冷
原始的解决办法
stateenum
用枚举类定义三种状态
package org.example.origin; |
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public enum stateenum { |
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power_off, fan_only, cool |
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} |
originaction
presspoweroff() 表示点开关按钮，presscool() 表示点击制冷按钮。
package org.example.origin; |
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public class originaction { |
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private stateenum stateenum; |
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public originaction() { |
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this.stateenum = stateenum.power_off; |
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} |
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public void presspoweroff() { |
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// 关机->吹风 |
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if (stateenum == stateenum.power_off) { |
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this.stateenum = stateenum.fan_only; |
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system.out.println("power on succeed."); |
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} else { |
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// 吹风或制冷->关机 |
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this.stateenum = stateenum.power_off; |
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system.out.println("power off succeed."); |
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} |
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} |
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public void presscool() { |
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if (stateenum == stateenum.power_off) { |
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system.out.println("cool failed because power off."); |
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} else if (stateenum == stateenum.fan_only) { |
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// 吹风->制冷 |
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this.stateenum = stateenum.cool; |
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system.out.println("open cool succeed."); |
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} else { |
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// 制冷->吹风 |
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this.stateenum = stateenum.fan_only; |
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system.out.println("close cool succeed"); |
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} |
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} |
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} |
origintest
编写测试类
package org.example.origin; |
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public class origintest { |
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public static void main(string[] args) { |
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originaction originaction = new originaction(); |
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originaction.presscool(); |
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originaction.presspoweroff(); |
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originaction.presscool(); |
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originaction.presscool(); |
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originaction.presspoweroff(); |
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} |
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} |
执行结果：
cool failed because power off.
power on succeed.
open cool succeed.
close cool succeed
power off succeed.
使用有限状态机解决
finitestatemachineenum
这里使用了 java 的枚举类，确保了类型约束。
package org.example.state; |
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public enum finitestatemachineenum { |
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power_off { |
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// 关机->吹风 |
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@override |
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public finitestatemachineenum presspoweroff() { |
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system.out.println("power on succeed."); |
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return finitestatemachineenum.fan_only; |
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} |
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// 无效 |
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@override |
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public finitestatemachineenum presscool() { |
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system.out.println("cool failed because power off."); |
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return finitestatemachineenum.power_off; |
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} |
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}, |
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fan_only { |
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// 吹风->关机 |
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@override |
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public finitestatemachineenum presspoweroff() { |
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system.out.println("power off succeed."); |
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return finitestatemachineenum.power_off; |
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} |
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// 吹风->制冷 |
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@override |
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public finitestatemachineenum presscool() { |
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system.out.println("open cool succeed."); |
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return finitestatemachineenum.cool; |
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} |
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}, |
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cool { |
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// 制冷->关机 |
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@override |
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public finitestatemachineenum presspoweroff() { |
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system.out.println("power off succeed."); |
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return finitestatemachineenum.power_off; |
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} |
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// 制冷->吹风 |
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@override |
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public finitestatemachineenum presscool() { |
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system.out.println("close cool succeed"); |
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return finitestatemachineenum.fan_only; |
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} |
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}; |
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public abstract finitestatemachineenum presspoweroff(); |
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public abstract finitestatemachineenum presscool(); |
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} |
finitestatemachinetest
编写测试类
package org.example.state; |
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public class finitestatemachinetest { |
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public static void main(string[] args) { |
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finitestatemachineenum stateenum = finitestatemachineenum.power_off; |
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stateenum.presscool() |
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.presspoweroff() |
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.presscool() |
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.presscool() |
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.presspoweroff(); |
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} |
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} |
执行结果：
cool failed because power off.
power on succeed.
open cool succeed.
close cool succeed
power off succeed.