一、引出状态模式

假设我们此刻有一个糖果机项目，那么我们知道正常一般糖果机提供应用户的行为有这么几种：投入硬币、动弹曲柄、退出硬币几种行为；那么糖果机呢一般有这几中状态，待机状态、持有硬币的筹备状态、运行状态即正在售出状态和初始状态 这么几种正常状态。 我们发明处于差异状态的时候，持有的行为是纷歧样的，图如下：

假如我们回收传统的要领来写代码，那么在投入硬币这个行为操纵的时候，我们会举办状态的判定，只有在处于待机状态环境下这种行为是正常的，而其他则非正常，那么其他行为也一样，都需要去先判定下当前的状态来举办操纵。获得的代码则为：

package study.designmode.statemode;

public class CandyMachine {

    final static int SoldOutState = 0; //初始状态
    final static int OnReadyState = 1;  //待机状态
    final static int HasCoin = 2;  //筹备状态
    final static int SoldState = 3;  //售出状态

    private int state = SoldOutState; //变量,用于存放当前的状态值
    private int count = 0; //糖果的数目

    public CandyMachine(int count) {
        this.count = count;
        if (count > 0) {
            state = OnReadyState;
        }
    }

    //投入硬币行为的时候，通过判定当前的状态来匹配所有的状态.
    public void insertCoin() {
        switch (state) {
        case SoldOutState:
            System.out.println("you can't insert coin,the machine sold out!");
            break;
        case OnReadyState: //只有在待机状态的时候,投入硬币行为正确,并将状态改变为筹备状态
            state = HasCoin;
            System.out
                    .println("you have inserted a coin,next,please turn crank!");
            break;
        case HasCoin:
            System.out.println("you can't insert another coin!");

            break;
        case SoldState:
            System.out.println("please wait!we are giving you a candy!");

            break;
        }

    }

    //回退硬币
    public void returnCoin() {
        switch (state) {
        case SoldOutState:
            System.out
                    .println("you can't return,you haven't inserted a coin yet!");
            break;
        case OnReadyState:
            System.out.println("you haven't inserted a coin yet!");
            break;
        case HasCoin:

            System.out.println("coin return!");
            state = OnReadyState;

            break;
        case SoldState:
            System.out.println("sorry,you already have turned the crank!");

            break;
        }

    }

    //动弹曲柄
    public void turnCrank() {
        switch (state) {
        case SoldOutState:
            System.out.println("you turned,but there are no candies!");
            break;
        case OnReadyState:
            System.out.println("you turned,but you haven't inserted a coin!");
            break;
        case HasCoin:
            System.out.println("crank turn...!");
            state = SoldState;
            dispense();
            break;
        case SoldState:
            System.out
                    .println("we are giving you a candy,turning another get nothing,!");
            break;
        }

    }

    //触发发放糖果行为
    private void dispense() {
        count = count - 1;
        System.out.println("a candy rolling out!");
        if (count > 0) {
            state = OnReadyState;
        } else {
            System.out.println("Oo,out of candies");
            state = SoldOutState;
        }

    }

    public void printstate() {

        switch (state) {
        case SoldOutState:
            System.out.println("***SoldOutState***");
            break;
        case OnReadyState:
            System.out.println("***OnReadyState***");
            break;
        case HasCoin:

            System.out.println("***HasCoin***");

            break;
        case SoldState:
            System.out.println("***SoldState***");
            break;
        }

    }
}

那么上面这种方法存在什么问题呢？首先很直观的感觉就是:

1.存在大量的switch case 语句 虽然可以用if else 也是一样的。

2.可扩展性差，而且一旦要插手一种新的状态，那么就会要修改所有的switch case 不切合开闭原则

3.没有回收面向工具的方法去封装

好比，这个时候，新增加了一种状态，赢家状态，即可以获取到两粒糖果；那么假如用上面的方法，必定是不切合开闭原则的，同时扩展性也是欠好的；那么我们有什么其它的方法来办理呢？

二、办理步伐