菜鸟笔记介绍
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.