public class CandyMachine {private final static int SOLD_OUT = 0; // 售罄状态private final static int NO_QUARTER = 1; // 无币状态,QUARTER==25美分==币private final static int HAS_QUARTER = 2; // 有币状态private final static int SOLD = 3; // 售卖状态private int state = SOLD_OUT;private int count = 0;public CandyMachine(int count) {this.count = count;if(count > 0) {this.state = NO_QUARTER;}}public void insertQuarter() { // client投币请求if(state == HAS_QUARTER) {System.out.println("you can't insert another quarter.");} else if(state == NO_QUARTER) {System.out.println("you insert a quarter.");state = HAS_QUARTER;} else if(state == SOLD_OUT) {System.out.println("you can't insert a quarter for the machine is sold out.");} else if(state == SOLD) {System.out.println("please wait, we're already gibing you a candy.");}}public void ejectQuarter() { // client请求退钱if(state == HAS_QUARTER) {System.out.println("quarter returned.");state = NO_QUARTER;} else if(state == NO_QUARTER) {System.out.println("you haven't inserted a quarter.");} else if(state == SOLD_OUT) {System.out.println("you can't eject for you haven't inserted a quarter yet.");} else if(state == SOLD) {System.out.println("sorry, you already trune the crank.");}}public void turnCrank() { // client转动曲柄动作if(state == HAS_QUARTER) {System.out.println("you turned, please wait....");state = SOLD;dispense();} else if(state == NO_QUARTER) {System.out.println("you turned but there is no quarter.");} else if(state == SOLD_OUT) {System.out.println("you truned but there's no candy.");} else if(state == SOLD) {System.out.println("turning twice doesn't get you another candy.");}}private void dispense() { // 分发糖果if(state == HAS_QUARTER) {System.out.println("no candy dispensed.");} else if(state == NO_QUARTER) {System.out.println("you need to insert a quarter first.");} else if(state == SOLD_OUT) {System.out.println("no candy dispensed.");} else if(state == SOLD) {System.out.println("a candy comes rolling out the slot.");count--;if(count == 0) {System.out.println("Oops, there's no candy.");state = SOLD_OUT;} else {state = NO_QUARTER;}}}@Overridepublic String toString() {String state_str = null;switch (state) {case SOLD_OUT: state_str = "SOLD_OUT"; break;case SOLD: state_str = "SOLD"; break;case NO_QUARTER: state_str = "NO_QUARTER"; break;case HAS_QUARTER: state_str = "HAS_QUARTER"; break;}return "=== I own " + count + " candies, and stay in " + state_str + " state. ===";}
}

public class CandyMachineTest {public static void main(String[] args) {CandyMachine cm = new CandyMachine(5);System.out.println(cm);System.out.println("====== 1st test: ======");cm.insertQuarter();cm.turnCrank();System.out.println(cm);System.out.println("====== 2nd test: ======");cm.insertQuarter();cm.ejectQuarter();//要求售卖机退钱cm.ejectQuarter();//要求售卖机第二次退钱System.out.println("====== 3rd test: ======");cm.insertQuarter();cm.ejectQuarter();cm.turnCrank();// 请求退钱后，不应该得到糖果System.out.println(cm);}
}

=== I own 5 candies, and stay in NO_QUARTER state. ===
====== 1st test: ======
you insert a quarter.
you turned, please wait....
a candy comes rolling out the slot.
=== I own 4 candies, and stay in NO_QUARTER state. ===
====== 2nd test: ======
you insert a quarter.
quarter returned.
you haven't inserted a quarter.
====== 3rd test: ======
you insert a quarter.
quarter returned.
you turned but there is no quarter.
=== I own 4 candies, and stay in NO_QUARTER state. ===

public abstract class State {protected String name;public abstract void insertQuarter();public abstract void ejectQuarter();public abstract void trunCrank();public abstract void dispense();public String getName() {return name;}
}

// 售罄状态
public class SoldOutState extends State {CandyMachine machine;public SoldOutState(CandyMachine machine) {super.name = "SoldOutState";this.machine = machine;}@Overridepublic void insertQuarter() {System.out.println("you can't insert a quarter for there's no candies.");       }@Overridepublic void ejectQuarter() {System.out.println("you have not inserted a quarter.");}@Overridepublic void trunCrank() {System.out.println("you turned but there is no quarter.");}@Overridepublic void dispense() {System.out.println("you need to insert a quarter first.");     }}

public class NoQuarterState extends State {CandyMachine machine;public NoQuarterState(CandyMachine machine) {super.name = "NoQuarterState";this.machine = machine;}@Overridepublic void insertQuarter() {System.out.println("you insert a quatter.");machine.setState(machine.getHasQuarterState());}@Overridepublic void ejectQuarter() {if(machine.getState() == machine.getHasQuarterState()) {System.out.println("returned a quarter.");machine.setState(machine.getNoQuarterState());} else {System.out.println("you have not inserted a quarter.");}}@Overridepublic void trunCrank() {System.out.println("you turned but there is no quarter.");}@Overridepublic void dispense() {System.out.println("you need to insert a quarter first.");       }
}

// 有币状态
public class HasQuarterState extends State {Random random = new Random();CandyMachine machine;public HasQuarterState(CandyMachine machine) {super.name = "HasQuarterState"; this.machine = machine;}@Overridepublic void insertQuarter() {System.out.println("you can't insert another quarter.");}@Overridepublic void ejectQuarter() { // client退钱请求System.out.println("quarter returned.");machine.setState(machine.getNoQuarterState());}@Overridepublic void trunCrank() { // 有币状态下，进行几率性中奖测试System.out.println("you turned , please waiting......");int winner = random.nextInt(5);System.out.println("\nrandom winner == " + winner);if(winner == 2 && machine.getCount() > 1) {machine.setState(machine.getWinnerState());} else {machine.setState(machine.getSoldState());}}@Overridepublic void dispense() {System.out.println("no candies dispensed.");      }
}

// 售卖状态
public class SoldState extends State {CandyMachine machine;public SoldState(CandyMachine machine) {super.name = "SoldState";this.machine = machine;}@Overridepublic void insertQuarter() {     System.out.println("please wait, we're already giving you a candy.");        }@Overridepublic void ejectQuarter() {System.out.println("sorry, you've already turned the crank.");}@Overridepublic void trunCrank() {System.out.println("turning twice doesn't get you another candy.");}@Overridepublic void dispense() {machine.releaseBall();if(machine.getCount() > 0) {machine.setState(machine.getNoQuarterState());} else {machine.setState(machine.getSoldOutState());}}
}

// 中奖状态
public class WinnerState extends State {CandyMachine machine;public WinnerState(CandyMachine machine) {this.machine = machine;}@Overridepublic void insertQuarter() {System.out.println("error.");}@Overridepublic void ejectQuarter() { // client退钱请求System.out.println("error.");}@Overridepublic void trunCrank() {System.out.println("error.");}@Overridepublic void dispense() {System.out.println("you're a winner. you get 2 candies for your quarter.");machine.releaseBall();if(machine.getCount() == 0) {machine.setState(machine.getSoldOutState());} else {machine.releaseBall();if(machine.getCount() > 0) {machine.setState(machine.getNoQuarterState());} else {System.out.println("Oops, out of candies.");machine.setState(machine.getSoldOutState());}}}
}

public class CandyMachine {private State winnerState; //中奖状态private State soldOutState; // 售罄状态private State noQuarterState; // 无币状态,QUARTER==25美分==币private State hasQuarterState; // 有币状态private State soldState; // 售卖状态private State state;private int count = 0;public CandyMachine(int count) {soldOutState = new SoldOutState(this);soldState = new SoldState(this);hasQuarterState = new HasQuarterState(this);noQuarterState = new NoQuarterState(this);winnerState = new WinnerState(this);state = soldOutState;this.count = count;if(count > 0) {state = noQuarterState;}}public void insertQuarter() { // client投币请求state.insertQuarter();}public void ejectQuarter() { // client请求退钱state.ejectQuarter();}public void turnCrank() { // client转动曲柄动作state.trunCrank();state.dispense();}public void releaseBall() { // 释放糖果System.out.println("a candy comes rolling out the slot....");if(count != 0) {count--;}}public State getState() {return state;}public void setState(State state) {this.state = state;}public State getSoldOutState() {return soldOutState;}public void setSoldOutState(State soldOutState) {this.soldOutState = soldOutState;}public State getSoldState() {return soldState;}public void setSoldState(State soldState) {this.soldState = soldState;}public State getHasQuarterState() {return hasQuarterState;}public void setHasQuarterState(State hasQuarterState) {this.hasQuarterState = hasQuarterState;}public State getNoQuarterState() {return noQuarterState;}public void setNoQuarterState(State noQuarterState) {this.noQuarterState = noQuarterState;}public int getCount() {return count;}public void setCount(int count) {this.count = count;}public State getWinnerState() {return winnerState;}public void setWinnerState(State winner) {this.winnerState = winner;} @Override  public String toString() {  String state_str = null;  switch (state.getName()) {  case "SoldOutState": state_str = "SOLD_OUT"; break;  case "SoldState": state_str = "SOLD"; break;  case "NoQuarterState": state_str = "NO_QUARTER"; break;  case "HasQuarterState": state_str = "HAS_QUARTER"; break;  }  return "=== I own " + count + " candies, and stay in " + state_str + " state. ===";  }
}

step4）测试用例

public class CandyMachineTest {public static void main(String[] args) {CandyMachine cm = new CandyMachine(50);System.out.println(cm);System.out.println("====== init state ======");System.out.println(cm);// 第一次测试cm.insertQuarter();cm.turnCrank();System.out.println(cm);// 第二次测试cm.turnCrank();System.out.println(cm);// 第3次测试： 在为投币的情况下退币请求cm.ejectQuarter();System.out.println(cm);System.out.println("\n\n ====== 下面进入循环测试（中奖）随机数==2表示中奖 ======");for (int i = 0; i < 5; i++) {cm.insertQuarter();cm.turnCrank();System.out.println(cm);}}
}

=== I own 50 candies, and stay in NO_QUARTER state. ===
====== init state ======
=== I own 50 candies, and stay in NO_QUARTER state. ===
you insert a quatter.
you turned , please waiting......random winner == 0
a candy comes rolling out the slot....
=== I own 49 candies, and stay in NO_QUARTER state. ===
you turned but there is no quarter.
you need to insert a quarter first.
=== I own 49 candies, and stay in NO_QUARTER state. ===
you have not inserted a quarter.
=== I own 49 candies, and stay in NO_QUARTER state. ========= 下面进入循环测试（中奖，为了演示方便，我这里的中奖率为20%，且 <span style="font-family: Arial, Helvetica, sans-serif;">随机数==2表示中奖</span><span style="font-family: Arial, Helvetica, sans-serif;">） ======</span>
you insert a quatter.
you turned , please waiting......random winner == 2
you're a winner. you get 2 candies for your quarter.
a candy comes rolling out the slot....
a candy comes rolling out the slot....
=== I own 47 candies, and stay in NO_QUARTER state. ===
you insert a quatter.
you turned , please waiting......random winner == 4
a candy comes rolling out the slot....
=== I own 46 candies, and stay in NO_QUARTER state. ===
you insert a quatter.
you turned , please waiting......random winner == 4
a candy comes rolling out the slot....
=== I own 45 candies, and stay in NO_QUARTER state. ===
you insert a quatter.
you turned , please waiting......random winner == 2
you're a winner. you get 2 candies for your quarter.
a candy comes rolling out the slot....
a candy comes rolling out the slot....
=== I own 43 candies, and stay in NO_QUARTER state. ===
you insert a quatter.
you turned , please waiting......random winner == 0
a candy comes rolling out the slot....
=== I own 42 candies, and stay in NO_QUARTER state. ===