状态模式深入思考

来源：互联网发布：python编程入门 epub 编辑：程序博客网时间：2024/05/09 09:05

状态模式的状态中的方法是促进状态转化的操作，当然也可以包括一些公共的行为，必须几个状态都有disply的方法，那这个方法可以放到抽象状态中。而不是说一种状态对应一个方法，这样理解是不对的。

我的一点思考：感觉，tcpconnection这个适合状态模式、上传下载的状态等等这些都较为适合使用这个模式。

以下是《head first设计模式》上的一个案例：从这个案例中可以看出，insertQuarter、ejectQuarter、turnCrank、dispense这几个方法可以促进状态之间的转化，这些方法对应着接口中的方法。不过每个具体的状态都可以有自己的个性（private方法）。

!!!
状态模式的难点就在于如何设计抽象接口中的几个方法。这才是他的难点所在。

/** * Created by annuoaichengzhang on 16/4/21. * 糖果机的案例 */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}

/** * Created by annuoaichengzhang on 16/4/21. *//* * 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    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");    }}

/** * Created by annuoaichengzhang on 16/4/21. *//* * 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");    }}

/** * Created by annuoaichengzhang on 16/4/21. *//* * 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 stub        System.out.println("You can't eject, you haven't inserted a quarter yet");    }    // 转动曲柄    public void turnCrank() {        // TODO Auto-generated method stub        System.out.println("You turned, but there are no gumballs");    }    // 发放糖果    public void dispense() {        // TODO Auto-generated method stub        System.out.println("No gumball dispensed");    }}

/** * Created by annuoaichengzhang on 16/4/21. *//* * 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());        }    }}

/** * Created by annuoaichengzhang on 16/4/21. *//* * 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    @Override    public void insertQuarter() {        // TODO Auto-generated method stub        System.out.println("Please wait, we're already giving you a gumball");    }    // 拒绝25分钱    @Override    public void ejectQuarter() {        // TODO Auto-generated method stub        System.out.println("Sorry,you have already turn crank");    }    // 转动曲柄    @Override    public void turnCrank() {        // TODO Auto-generated method stub        System.out.println("trun twice ,doesn't give you anthor gamball!");    }    // 发放糖果    @Override    public void dispense() {        // TODO Auto-generated method stub        System.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());            }        }    }}

/** * Created by annuoaichengzhang on 16/4/21. *//* *  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NoQuarterState        if(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--;        }    }}

/** * Created by annuoaichengzhang on 16/4/21. *//* * 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("****************************************");    }}

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