状态模式

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状态模式允许对象在对象内部状态改变时改变它的行为，对象看起来好像修改了他的类
现在又一个糖果机，我们需要写程序来控制它的出售行为，如图
这里写图片描述
当然我们可以用一堆if，else语句俩控制它。但是如果程序需要加入其他的状态，那么整个程序就会变得越来越乱。这时我们需要状态模式来重构程序。

java代码

// 状态接口public interface State {    void insertCoin();    void ejectCoin();    void turnCrank();    void dispense();}// 没有投币状态public class NoCoinState implements State {    private GumballMachine machine;    public NoCoinState(GumballMachine machine) {        this.machine = machine;    }    @Override    public void insertCoin() {        machine.setState(machine.getHasCoinState());        System.out.println("Your inserted a coin");    }    @Override    public void ejectCoin() {        System.out.println("Your have not inserted a coin");    }    @Override    public void turnCrank() {        System.out.println("You turned, but there is no coin");    }    @Override    public void dispense() {        System.out.println("You need to pay first");    }}// 已投币状态public class HasCoinState implements State {    private GumballMachine machine;    public HasCoinState(GumballMachine machine) {        this.machine = machine;    }    @Override    public void insertCoin() {        System.out.println("You can not insert another coin");    }    @Override    public void ejectCoin() {        machine.setState(machine.getNoCoinState());        System.out.println("Coin returned");    }    @Override    public void turnCrank() {        machine.setState(machine.getSoldState());        System.out.println("You turned ... ");    }    @Override    public void dispense() {        System.out.println("No gumball dispensed");    }}// 已出售状态（正在出货）public class SoldState implements State {    private GumballMachine machine;    public SoldState(GumballMachine machine) {        this.machine = machine;    }    @Override    public void insertCoin() {        System.out.println("Please wait, we are already giving you a gumball");    }    @Override    public void ejectCoin() {        System.out.println("Sorry, you already turned the crank");    }    @Override    public void turnCrank() {        System.out.println("Turning twice does not get you another gumball!");    }    @Override    public void dispense() {        if (machine.getGumballNum() > 0) {            machine.setGumballNum(machine.getGumballNum() - 1);            machine.setState(machine.getNoCoinState());            System.out.println("A gumball comes rolling out the slot ... ");        }        if (machine.getGumballNum() <= 0) {            machine.setState(machine.getSoldOutState());            System.out.println("Oops, out of gumballs!");        }    }}// 售罄状态public class SoldOutState implements State {    private GumballMachine machine;    public SoldOutState(GumballMachine machine) {        this.machine = machine;    }    @Override    public void insertCoin() {        System.out.println("You can not insert a coin, this machine is sold out");    }    @Override    public void ejectCoin() {        System.out.println("Your have not inserted a coin");    }    @Override    public void turnCrank() {        System.out.println("You turned, but there are no gumballs");    }    @Override    public void dispense() {        System.out.println("No gumball dispensed");    }}// 测试类public class Test {    public static void main(String[] args) {        new Test().test();    }    private void test() {        GumballMachine machine = new GumballMachine(5);        machine.insertCoin();        machine.turnCrank();    }}

注：

当糖果的状态改变的时候，他的所有行为都已经改变

参考文章
1. Head First 设计模式

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