<<Head First设计模式>>之状态模式学习篇
最近在公司闲着没事干，看了一下<<Head First设计模式>>一书，感觉还蛮有意思，设计模式涉及到OO的设计思想和OO的设计原则。这本书是采用Java语言描述的。由于我比较熟悉C++，所以看完之后想使用C++来实现。由于想要结合状态模式和工厂模式做Windows计算器，所以重点看了一下状态模式，并且将<<Head First设计模式>>一书中以糖果机为例子讲述状态模式的例子使用C++做了一篇，加深我对状态模式的理解。大家如果看了之后觉得我写得有什么问题，欢迎大家提出自己的见解，大家交流学习一下，毕竟我也只是设计模式的初学者而已，开发经验不足。
下面是<<Head First设计模式>>一书中糖果机的状态图及相应的Java代码和C++实现代码：
糖果机共有5个状态：没有25分钱、有25分钱、售出糖果、糖果售罄、赢家状态，这里从下面的UML状态图可以看到，Visio里使用椭圆形表示状态，还有引发糖果机状态发生转换的事件动作。
我使用Visio2003绘制的糖果机状态图，画得不太好，可能不是很标准，UML对于面向对象的软件设计很重要。
对应的Java代码如下：
??//State.javapackage State;/* * 状态接口State */public interface State { public void insertQuarter(); // 投入25分钱 public void ejectQuarter(); // 拒绝25分钱 public void turnCrank(); // 转动曲柄 public void dispense(); // 发放糖果}//NoQuarterState.javapackage State;import State.GumballMachine;/* * 没有25分钱状态，实现了State接口 */public class NoQuarterState implements State{GumballMachine gumballMachine;public NoQuarterState(GumballMachine gumballMachine){this.gumballMachine=gumballMachine;}// 投入25分钱public void insertQuarter() {System.out.println("You insert a quarter");gumballMachine.setState(gumballMachine.getHasQuarterState());} // 拒绝25分钱public void ejectQuarter() {System.out.println("You haven't insert a quarter");} // 转动曲柄public void turnCrank() {System.out.println("You turned crank,but you there's no quarter");}// 发放糖果public void dispense() {System.out.println("You need to pay first");}}//HasQuarterState.javapackage State;import java.util.Random;import State.GumballMachine;/* * 有25分钱状态，实现了State接口 */public class HasQuarterState implements State {Random randomWinner = new Random(System.currentTimeMillis()); //首先我们增加一个随机数产生器，产生10%赢的机会GumballMachine gumballMachine;public HasQuarterState(GumballMachine gumballMachine){this.gumballMachine = gumballMachine;}// 投入25分钱public void insertQuarter() {System.out.println("You can not insert anther quarter");}// 拒绝25分钱public void ejectQuarter() {System.out.println("Quarter returned");gumballMachine.setState(gumballMachine.getNoQuarterState());} // 转动曲柄public void turnCrank() {System.out.println("You turned...");int winner = randomWinner.nextInt(10);System.out.println("winner =" + winner);if((winner ==0) && (gumballMachine.getCount() > 1)) {gumballMachine.setState(gumballMachine.getWinnerState());} else {gumballMachine.setState(gumballMachine.getSoldState());}}// 发放糖果public void dispense() {System.out.println("No gumball dispensed");}}//SoldState.javapackage State;import State.GumballMachine;/* * 售出糖果状态，实现了State接口 */public class SoldState implements State{GumballMachine gumballMachine;public SoldState(GumballMachine gumballMachine) {this.gumballMachine = gumballMachine;}// 投入25分钱public void insertQuarter() {System.out.println("Please wait, we're already giving you a gumball");}// 拒绝25分钱public void ejectQuarter() {System.out.println("Sorry,you have already turn crank");}// 转动曲柄public void turnCrank() {System.out.println("trun twice ,doesn't give you anthor gamball!");}// 发放糖果public void dispense() {gumballMachine.releaseBall();if(gumballMachine.getCount()>0){gumballMachine.setState(gumballMachine.getNoQuarterState());} else {System.out.println("Opps,out of gamball!");gumballMachine.setState(gumballMachine.getSoldOutState());}}}//SoldOutState.javapackage State;import State.GumballMachine;/* * 通过售罄状态，实现了State接口 */public class SoldOutState implements State{GumballMachine gumballMachine;public SoldOutState(GumballMachine gumballMachine){this.gumballMachine=gumballMachine;} // 投入25分钱public void insertQuarter() {System.out.println("You can't insert a quarter, the machine is sold out");}// 拒绝25分钱public void ejectQuarter() {// TODO Auto-generated method stubSystem.out.println("You can't eject, you haven't inserted a quarter yet");} // 转动曲柄public void turnCrank() {// TODO Auto-generated method stubSystem.out.println("You turned, but there are no gumballs");}// 发放糖果public void dispense() {// TODO Auto-generated method stubSystem.out.println("No gumball dispensed");}}//WinnerState.javapackage State;import State.GumballMachine;/* * 赢家状态，实现了State接口 */public class WinnerState implements State{ GumballMachine gumballMachine; public WinnerState(GumballMachine gumballMachine){ this.gumballMachine = gumballMachine; } // 投入25分钱 @Overridepublic void insertQuarter() {// TODO Auto-generated method stub System.out.println("Please wait, we're already giving you a gumball");} // 拒绝25分钱 @Overridepublic void ejectQuarter() {// TODO Auto-generated method stub System.out.println("Sorry,you have already turn crank");} // 转动曲柄@Overridepublic void turnCrank() {// TODO Auto-generated method stubSystem.out.println("trun twice ,doesn't give you anthor gamball!");}// 发放糖果@Overridepublic void dispense() {// TODO Auto-generated method stubSystem.out.println("You're a Winner! You get two gumballs for your quarter");gumballMachine.releaseBall(); if(gumballMachine.getCount() == 0) { gumballMachine.setState(gumballMachine.getSoldOutState()); } else { gumballMachine.releaseBall(); if(gumballMachine.getCount()>0){gumballMachine.setState(gumballMachine.getNoQuarterState());} else { System.out.println("Opps,out of gamball!"); gumballMachine.setState(gumballMachine.getSoldOutState()); } }}}//糖果机上下文环境类Java源文件 GumballMachine.javapackage State;import State.HasQuarterState;import State.NoQuarterState;import State.SoldOutState;import State.SoldState;import State.WinnerState;import State.State;/* * 糖果机器上下文环境接口类 GumballMachine */public class GumballMachine {//状态实例State soldOutState;State noQuarterState;State hasQuarterState;State soldState;State winnerState;// 实例变量state，初始化为糖果售罄状态State state = soldOutState; // 记录机器内装有糖果的数目，开始机器是没有装糖果的int count=0;// 构造器取得糖果的初始数目并把它放在一个实例变量count中public GumballMachine(int numberGumballs) {// 每种状态都创建一个状态实例soldOutState=new SoldOutState(this);noQuarterState=new NoQuarterState(this);hasQuarterState=new HasQuarterState(this);soldState=new SoldState(this);winnerState = new WinnerState(this);this.count = numberGumballs;// 若超过0颗糖果，就将状态设置为NoQuarterStateif(numberGumballs > 0) {state = noQuarterState;}}// 取得机器内的糖果数目public int getCount() {return count;} // 取得糖果售罄状态public State getSoldOutState() {return soldOutState;} // 取得没有25分钱状态public State getNoQuarterState() {return noQuarterState;} // 取得拥有25分钱public State getHasQuarterState() {return hasQuarterState;} // 取得售出糖果状态public State getSoldState() {return soldState;}// 取得赢家状态public State getWinnerState() {return winnerState;} // 投入25分钱public void insertQuarter(){state.insertQuarter();}// 拒绝25分钱public void ejectQuarter(){state.ejectQuarter();}// 转动曲柄public void turnCrank(){state.turnCrank();state.dispense();}// 设置状态public void setState(State state){this.state=state;}// 糖果滚出来一个public void releaseBall(){System.out.println("A gumball comes rolling out of the solt...");if(count!=0){count--;}}}//测试糖果机的Java源文件 GumballMachineTestDrive.javapackage State;/* * 糖果机测试驱动程序：GumballMachineTestDrive.java */public class GumballMachineTestDrive {/** * @param args */public static void main(String[] args) { GumballMachine gumballMachine = new GumballMachine(5); System.out.println(gumballMachine); System.out.println("The current gumball number is:" + gumballMachine.getCount()); System.out.println("****************************************"); gumballMachine.insertQuarter(); gumballMachine.turnCrank(); System.out.println(gumballMachine); System.out.println("The current gumball number is:" + gumballMachine.getCount()); System.out.println("****************************************"); gumballMachine.insertQuarter(); gumballMachine.turnCrank(); System.out.println(gumballMachine); System.out.println("The current gumball number is:" + gumballMachine.getCount()); System.out.println("****************************************"); gumballMachine.insertQuarter(); gumballMachine.turnCrank(); System.out.println(gumballMachine); System.out.println("The current gumball number is:" + gumballMachine.getCount()); System.out.println("****************************************");}}运行结果截图如下：
对应的C++代码如下：
//State抽象基类//State.h#pragma onceclass State{public:State(void);public:~State(void);public:// 投入25分钱virtual void insertQuarter(void)=0;public:// 退回25分钱virtual void ejectQuarter(void)=0;public:// 转动曲柄virtual void turnCrank(void)=0;public:// 发放糖果virtual void dispense(void)=0;};//State.cpp#include "State.h"State::State(void){}State::~State(void){}//没有25分钱状态类 NoQuarterState//NoQuarterState.h#pragma once#include "state.h"#include "GumballMachine.h"class NoQuarterState :public State{public:NoQuarterState(GumballMachine *pGumballMachine);public:~NoQuarterState(void);public:// 投入25分钱void insertQuarter(void);public:// 退回25分钱void ejectQuarter(void);public:// 转动曲柄void turnCrank(void);public:// 发放糖果void dispense(void);private:// 糖果机实例变量GumballMachine *m_pGumballMachine;};//NoQuarterState.cpp#include "NoQuarterState.h"#include <iostream>using namespace std;NoQuarterState::NoQuarterState(GumballMachine *pGumballMachine){this->m_pGumballMachine = pGumballMachine;}NoQuarterState::~NoQuarterState(void){}// 投入25分钱void NoQuarterState::insertQuarter(void){cout<<"You inserted a quarter"<<endl;m_pGumballMachine->setState(m_pGumballMachine->getHasQuarterState());}// 退回25分钱void NoQuarterState::ejectQuarter(void){cout<<"You haven't inserted a quarter"<<endl;}// 转动曲柄void NoQuarterState::turnCrank(void){cout<<"You turned, but there's no quarter"<<endl;}// 发放糖果void NoQuarterState::dispense(void){cout<<"You need to pay first"<<endl;}//有25分钱状态 HasQuarterState//HasQuarterState.h#pragma once#include "state.h"#include "GumballMachine.h"class HasQuarterState :public State{public:HasQuarterState(GumballMachine *pGumballMachine);public:~HasQuarterState(void);public:// 投入25分钱void insertQuarter(void);public:// 退回25分钱void ejectQuarter(void);public:// 转动曲柄void turnCrank(void);public:// 发放糖果void dispense(void);private:// 糖果机实例变量GumballMachine *m_pGumballMachine;};//HasQuarterState.cpp#include "HasQuarterState.h"#include <iostream>#include <cstdlib>#include <ctime>using namespace std;HasQuarterState::HasQuarterState(GumballMachine *pGumballMachine){this->m_pGumballMachine = pGumballMachine;}HasQuarterState::~HasQuarterState(void){}// 投入25分钱void HasQuarterState::insertQuarter(void){cout<<"You can't insert another quarter"<<endl;}// 退回25分钱void HasQuarterState::ejectQuarter(void){cout<<"Quarter returned"<<endl;m_pGumballMachine->setState(m_pGumballMachine->getNoQuarterState());}// 转动曲柄void HasQuarterState::turnCrank(void){cout<<"You turned..."<<endl;// srand(time(0)); //用时间作种子，使每次随即的数字不一样//int winner = (int)(10.0*rand()/(RAND_MAX+1.0)); // 产生随机数int winner = rand()%10; // 产生随机数cout<<winner<<endl;if((winner == 3) && (m_pGumballMachine->getCount()>1)){ m_pGumballMachine->setState(m_pGumballMachine->getWinnerState());}else{m_pGumballMachine->setState(m_pGumballMachine->getSoldState());}}// 发放糖果void HasQuarterState::dispense(void){cout<<"No gumball dispensed"<<endl;}//售出糖果状态 SoldState//SoldState.h#pragma once#include "state.h"#include "GumballMachine.h"class SoldState :public State{public:SoldState(GumballMachine *pGumballMachine);public:~SoldState(void);public:// 投入25分钱void insertQuarter(void);// 退回25分钱void ejectQuarter(void);// 转动曲柄void turnCrank(void);// 发放糖果void dispense(void);private:// 糖果机实例变量GumballMachine *m_pGumballMachine;};//SoldState.cpp#include "SoldState.h"#include <iostream>using namespace std;SoldState::SoldState(GumballMachine *pGumballMachine){this->m_pGumballMachine = pGumballMachine;}SoldState::~SoldState(void){}// 投入25分钱void SoldState::insertQuarter(void){cout<<"Please wait, we're already giving you a gumball"<<endl;}// 退回25分钱void SoldState::ejectQuarter(void){ cout<<"Sorry, you already turned the Crank"<<endl;}// 转动曲柄void SoldState::turnCrank(void){cout<<"Turning twice doesn't get you another gumball!"<<endl;}// 发放糖果void SoldState::dispense(void){m_pGumballMachine->releaseBall();if(m_pGumballMachine->getCount()>0){m_pGumballMachine->setState(m_pGumballMachine->getNoQuarterState());}else{cout<<"Oops, out of gumballs!"<<endl;m_pGumballMachine->setState(m_pGumballMachine->getSoldOutState());}}//糖果售罄状态 SoldOutState类//SoldOutState.h#pragma once#include "state.h"#include "GumballMachine.h"class SoldOutState :public State{public:SoldOutState(GumballMachine *pGumballMachine);public:~SoldOutState(void);public:// 投入25分钱void insertQuarter(void);// 退回25分钱void ejectQuarter(void);// 转动曲柄void turnCrank(void);// 发放糖果void dispense(void);private:// 糖果机实例变量GumballMachine *m_pGumballMachine;};//SoldOutState.cpp#include "SoldOutState.h"#include <iostream>using namespace std;SoldOutState::SoldOutState(GumballMachine *pGumballMachine){this->m_pGumballMachine = pGumballMachine;}SoldOutState::~SoldOutState(void){}// 投入25分钱void SoldOutState::insertQuarter(void){cout<<"You can't insert a quarter, the machine is sold out"<<endl;}// 退回25分钱void SoldOutState::ejectQuarter(void){cout<<"You can't eject, you haven't inserted a quarter yet"<<endl;}// 转动曲柄void SoldOutState::turnCrank(void){cout<<"You turned, but there are no gumballs"<<endl;}// 发放糖果void SoldOutState::dispense(void){cout<<"No gumball dispensed"<<endl;}//赢家状态 WinnerState类//WinnerState.h#pragma once#include "state.h"#include "GumballMachine.h"class WinnerState :public State{public:WinnerState(GumballMachine *pGumballMachine);public:~WinnerState(void);public:// 投入25分钱void insertQuarter(void);public:// 退回25分钱void ejectQuarter(void);public:// 转动曲柄void turnCrank(void);public:// 发放糖果void dispense(void);private:// 糖果机实例变量GumballMachine *m_pGumballMachine;};//WinnerState.cpp#include "WinnerState.h"#include <iostream>using namespace std;WinnerState::WinnerState(GumballMachine *pGumballMachine){this->m_pGumballMachine = pGumballMachine;}WinnerState::~WinnerState(void){}// 投入25分钱void WinnerState::insertQuarter(void){cout<<"Please wait, we're already giving you a gumball"<<endl;}// 退回25分钱void WinnerState::ejectQuarter(void){cout<<"Sorry, you already turned the Crank"<<endl;}// 转动曲柄void WinnerState::turnCrank(void){cout<<"Turning twice doesn't get you another gumball!"<<endl;}// 发放糖果void WinnerState::dispense(void){cout<<"You're a Winner! You get two gumballs for your quarter";m_pGumballMachine->releaseBall();if(m_pGumballMachine->getCount() == 0){ m_pGumballMachine->setState(m_pGumballMachine->getSoldOutState());}else{ m_pGumballMachine->releaseBall(); if(m_pGumballMachine->getCount()>0){ m_pGumballMachine->setState(m_pGumballMachine->getNoQuarterState()); }else{ cout<<"Oops, out of gumballs!"<<endl; m_pGumballMachine->setState(m_pGumballMachine->getSoldOutState()); }}}//糖果机 上下文环境GumballMachine类//GumballMachine.h#pragma once#include "State.h"class GumballMachine{public:GumballMachine(int numberGumballs=0);public:~GumballMachine(void);private:// 状态类的指针State* m_pState;private:// 记录机器内的糖果数目int m_count;State* m_pSoldOutState;State* m_pNoQuarterState;State* m_pHasQuarterState;State* m_pSoldState;State* m_pWinnerState;public:void insertQuarter(void);public:// 退回25分钱void ejectQuarter(void);public:// 转动曲柄void turnCrank(void);public:// 设置状态void setState(State* pState);public:// 释放糖果void releaseBall(void);public:// 获取当前糖果的数目int getCount(void);// 获取发放糖果状态State* getSoldState(void);// 获取拥有25分钱状态State* getHasQuarterState(void);// 获取没有25分钱状态State* getNoQuarterState(void);// 获取糖果售罄状态State* getSoldOutState(void);public:// 获取赢家状态State* getWinnerState(void);};//GumballMachine.cpp#include "GumballMachine.h"#include "NoQuarterState.h"#include "HasQuarterState.h"#include "SoldOutState.h"#include "SoldState.h"#include "WinnerState.h"#include <iostream>using namespace std;GumballMachine::GumballMachine(int numberGumballs){m_pSoldOutState = new SoldOutState(this);m_pNoQuarterState = new NoQuarterState(this);m_pHasQuarterState = new HasQuarterState(this);m_pSoldState = new SoldState(this);this->m_count = numberGumballs;m_pState = m_pSoldOutState;if(numberGumballs>0){m_pState = m_pNoQuarterState;}}GumballMachine::~GumballMachine(void){ delete m_pSoldOutState; delete m_pNoQuarterState;delete m_pHasQuarterState;delete m_pSoldState;}void GumballMachine::insertQuarter(void){ m_pState->insertQuarter();}// 退回25分钱void GumballMachine::ejectQuarter(void){m_pState->ejectQuarter();}// 转动曲柄void GumballMachine::turnCrank(void){m_pState->turnCrank();m_pState->dispense();}// 设置状态void GumballMachine::setState(State* pState){this->m_pState = pState;}// 释放糖果void GumballMachine::releaseBall(void){cout<<"A gumball comes rolling out of the solt...";if(m_count != 0){m_count = m_count -1;}}// 获取当前糖果的数目int GumballMachine::getCount(void){return m_count;}// 获取发放糖果状态State* GumballMachine::getSoldState(void){return m_pSoldState;}// 获取拥有25分钱状态State* GumballMachine::getHasQuarterState(void){ return m_pHasQuarterState;}// 获取没有25分钱状态State* GumballMachine::getNoQuarterState(void){return m_pNoQuarterState;}// 获取糖果售罄状态State* GumballMachine::getSoldOutState(void){return m_pSoldOutState;}// 获取赢家状态State* GumballMachine::getWinnerState(void){return m_pWinnerState;}//测试主函数文件 TestDriver.cpp#include "GumballMachine.h"#include <iostream>using namespace std;int main(){ srand(time(NULL)); //以系统时间作为种子，设置随机数种子GumballMachine *pGumballMachine = new GumballMachine(5);pGumballMachine->insertQuarter();pGumballMachine->turnCrank();cout<<"the gumball count is:"<<pGumballMachine->getCount()<<endl;pGumballMachine->insertQuarter();pGumballMachine->turnCrank();cout<<"the gumball count is:"<<pGumballMachine->getCount()<<endl;pGumballMachine->insertQuarter();pGumballMachine->turnCrank();cout<<"the gumball count is:"<<pGumballMachine->getCount()<<endl;pGumballMachine->insertQuarter();pGumballMachine->turnCrank();cout<<"the gumball count is:"<<pGumballMachine->getCount()<<endl;pGumballMachine->insertQuarter();pGumballMachine->turnCrank();cout<<"the gumball count is:"<<pGumballMachine->getCount()<<endl;pGumballMachine->insertQuarter();pGumballMachine->turnCrank();cout<<"the gumball count is:"<<pGumballMachine->getCount()<<endl;pGumballMachine->insertQuarter();pGumballMachine->turnCrank();cout<<"the gumball count is:"<<pGumballMachine->getCount()<<endl;return 0;}
下面是程序运行结果截图：
记得以前在学校学Java得时候做的实验报告里面有一个关于地铁十字旋转门（turnstile）的状态模式练习，我感觉那个例子还比较好理解，因为来源于日常生活，例子描述如下：
在地铁十字旋转门（turnstile）的操作中，可以找到一个简单的有限状态机（FSM）。这个装置控制着乘客通往列车站台的大门。下面这个状态图展示了地铁十字转门的初步状态机。
状态图由四个部分组成。图中的矩形框表示一个状态（state），箭头表示状态的迁移，箭头上面有两个元素：前面那个是事件（event），后面那个是响应动作（action）。
(1)若状态机在Locked（锁）状态，收到一个coin(投币)事件，则执行unlock（开门）操作，并迁移到Unlocked（开）状态。
(2)若状态机在Locked（锁）状态，收到一个pass（人员通过）事件，则执行alarm（警报）操作，没有状态迁移。
(3)若状态机在Unlocked（开）状态，收到一个pass（人员通过）事件，则执行lock操作，并迁移到Locked（锁）状态。
(4)若状态机在Unlocked（开）状态，收到一个coin（投币）事件，则执行refund（退款）操作，没有状态迁移。
我们用一般的方法描述这件事应该是这样：
/**用TurnstileController封装旋转门能做的所有操作*/class TurnstileController {public void unlock(){System.out.println("正在执行开门操作…");}public void alarm(){System.out.println("注意! 有人强行越过旋转门…");}public void lock(){System.out.println("正在执行关门操作…");}public void refund(){System.out.println("退款中…");}}/**Turnstile：旋转门类*/class Turnstile {//用来代表状态的两个常量public static final int LOCKED = 0;public static final int UNLOCKED = 1;//用来代表事件的常量public static final int COIN = 0;public static final int PASS = 1;//当前旋转门的状态public int state = LOCKED;public TurnstileController tController;public Turnstile(TurnstileController tController){this.tController = tController;}//当新的事件发生时调用此方法，同时把事件代码传递给它public void eventHappen(int event){switch(state){case LOCKED:switch(event){case COIN:tController.unlock();state = UNLOCKED;break;case PASS:tController.alarm();break;}break;case UNLOCKED:switch(event){case COIN:tController.refund();break;case PASS:tController.lock();state = LOCKED;break;}break;}}}public class TurnstileTest {public static void main(String [] args){Turnstile turnstile = new Turnstile(new TurnstileController());turnstile.eventHappen(Turnstile.COIN);turnstile.eventHappen(Turnstile.PASS);turnstile.eventHappen(Turnstile.PASS);turnstile.eventHappen(Turnstile.COIN);turnstile.eventHappen(Turnstile.COIN);}}
但是这种实现方式至少有以下两个问题：
1）当状态数目不是很多的时候，Switch/Case可能可以搞定。但是当状态数目很多的时候（实际系统中也正是如此），维护一大组的Switch/Case语句将是一件异常困难并且容易出错的事情。
2）状态逻辑和动作实现没有分离。在很多的系统实现中，动作的实现代码直接写在状态的逻辑当中。这带来的后果就是系统的扩展性和维护得不到保证。
下面介绍State模式：在State模式中我们将状态逻辑和动作实现进行分离。当一个操作中要维护大量的case分支语句，并且这些分支依赖于对象的状态。State模式将每一个分支都封装到独立的类中。State模式典型的类图为：
State接口定义了所有状态的共同接口（能够发生的所有事件），任何状态都实现这个接口，这样一来，状态之间可以相互替换
Context（上下文）拥有一个当前的内部状态
不管什么时候发生一个事件(someEventHappen),Context将委托给具体的状态类去处理
具体状态，处理Context的请求，每一个具体状态实现了在该状态下，针对某一事件的特定响应动作和下一步的状态迁移
上面这幅图来源于<<Head First设计模式>>的状态模式章节。
代码如下：
interface State{public void someEventHappen(Context c);}class StateA implements State{public void someEventHappen(Context c){c.actionA();c.state = new StateB();}}class StateB implements State{public void someEventHappen(Context c){c.actionB();c.state = new StateA();}}class Context{public State state = new StateA();public void someEventHappen(){state.someEventHappen(this);}public void actionA(){System.out.println("action A is going on...");}public void actionB(){System.out.println("aciton B is going on...");}}public class StateTest{public static void main(String [] args){Context c = new Context();c.someEventHappen();c.someEventHappen();}}
注意该代码实现了如下的状态机：
你的任务：
参考以上描述的状态模式，利用状态模式重新设计并编写“地铁十字旋转门（turnstile）”问题。
下面是我的Java实现代码，不知道对不对。
//MyTurstileTest.javainterface State{public abstract void DropCoinEventHappen(Context c); public abstract void PassEventHappen(Context c);}class Context { private State state = new LockedState(); public void CoinEventHappen(){ state.DropCoinEventHappen(this); } public void PassEventHappen(){ state.PassEventHappen(this); } public void unlock(){System.out.println("正在执行开门操作.......");state = new UnLockedState(); }public void alarm(){System.out.println("注意! 有人强行越过旋转门.......");state = new LockedState();}public void lock(){System.out.println("正在执行关门操作........");state = new LockedState(); }public void refund(){System.out.println("退款中........"); state = new UnLockedState();} }class LockedState implements State{public void DropCoinEventHappen(Context c){ c.unlock();//执行开门操作} public void PassEventHappen(Context c){c.alarm();//报警 }}class UnLockedState implements State{public void DropCoinEventHappen(Context c){ c.refund();//退款}public void PassEventHappen(Context c){c.lock();//执行关门操作}}public class MyTurstileTest{public static void main(String[] args){Context c = new Context();System.out.println("地铁十字旋转门初始态为关的状态......");//起始状态地铁十字旋转门（turnstile）默认处于关的状态c.CoinEventHappen();//turnstile状态为关时，发生投币操作，事件发生后turnstile状态为开c.PassEventHappen();//turnstile状态为开时，发生人员通过事件,事件发生后turnstile状态为关c.PassEventHappen();//turnstile状态为关时，发生人员通过事件，事件发生后turnstile状态为开c.CoinEventHappen();//turstile状态为关时，发生投币操作，事件发生后turnstile状态为开}}下面是程序运行代码运行结果的贴图
另外我想使用MFC结合状态模式和工厂模式做一个标准版的Windows计算器，大概分成左操作数状态、操作符状态、右操作数状态、结果状态、错误异常状态这5个状态，然后可能还要区分单目运算符和双目运算符等等，等我做完这个练习后把关键的状态图和C++相关类设计代码也传上来，算是对状态模式学习的一个总结吧。