在上一次的文章里，我们看到，需求的变更，迫使我们需要重新改造现有的糖果机代码来符合这个新提的需求。但是，也并没有难倒我们，至少我们在文末给出了思路和类图，不知道你想的怎么样了呢。

我们不来虚的，直接进入正题，开启我们的学习之旅。

实现我们的状态类

现在是实现一个状态的时候了：我们知道我们要的行为是什么，我们只需要把它变成代码。我们打算完全遵守所写下的状态机代码，但是这一次是分散在不同的类中。比如我们以NoQuarterState类为例。

public class NoQuarterState implements State {
    GumballMachine gumballMachine;
 
    public NoQuarterState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }
 
    public void insertQuarter() {
        System.out.println("You inserted a quarter");
        gumballMachine.setState(gumballMachine.getHasQuarterState());
    }
 
    public void ejectQuarter() {
        System.out.println("You haven't inserted a quarter");
    }
 
    public void turnCrank() {
        System.out.println("You turned, but there's no quarter");
     }
 
    public void dispense() {
        System.out.println("You need to pay first");
    } 
    
}

在完成这些状态类之前，我们需要重新改造糖果机，好让你了解这一切的原理。我们把原来使用整数代表的状态改为状态对象:

    State soldOutState;
    State noQuarterState;
    State hasQuarterState;
    State soldState;
 
    State state;
    int count = 0;

这样，我们就有了一个完整的糖果机类

public class GumballMachine {
 
    State soldOutState;
    State noQuarterState;
    State hasQuarterState;
    State soldState;
 
    State state;
    int count = 0;
 
    public GumballMachine(int numberGumballs) {
        soldOutState = new SoldOutState(this);
        noQuarterState = new NoQuarterState(this);
        hasQuarterState = new HasQuarterState(this);
        soldState = new SoldState(this);

        this.count = numberGumballs;
        if (numberGumballs > 0) {
            state = noQuarterState;
        } else {
            state = soldOutState;
        }
    }
 
    public void insertQuarter() {
        state.insertQuarter();
    }
 
    public void ejectQuarter() {
        state.ejectQuarter();
    }
 
    public void turnCrank() {
        state.turnCrank();
        state.dispense();
    }
 
    void releaseBall() {
        System.out.println("A gumball comes rolling out the slot...");
        if (count != 0) {
            count = count - 1;
        }
    }
 
    // 后面部分省略
}

好了，这样子，我们就能继续实现更多的状态类了。比如我们能实现HasQuarterState和SoldState类

public class HasQuarterState implements State {
    GumballMachine gumballMachine;
 
    public HasQuarterState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }
  
    public void insertQuarter() {
        System.out.println("You can't insert another quarter");
    }
 
    public void ejectQuarter() {
        System.out.println("Quarter returned");
        gumballMachine.setState(gumballMachine.getNoQuarterState());
    }
 
    public void turnCrank() {
        System.out.println("You turned...");
        gumballMachine.setState(gumballMachine.getSoldState());
    }

    public void dispense() {
        System.out.println("No gumball dispensed");
    }
    
}

public class SoldState implements State {
 
    GumballMachine gumballMachine;
 
    public SoldState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }
       
    public void insertQuarter() {
        System.out.println("Please wait, we're already giving you a gumball");
    }
 
    public void ejectQuarter() {
        System.out.println("Sorry, you already turned the crank");
    }
 
    public void turnCrank() {
        System.out.println("Turning twice doesn't get you another gumball!");
    }
 
    public void dispense() {
        gumballMachine.releaseBall();
        if (gumballMachine.getCount() > 0) {
            gumballMachine.setState(gumballMachine.getNoQuarterState());
        } else {
            System.out.println("Oops, out of gumba