设计模式之状态模式（二）_设计模式

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 gumballs!");
            gumballmachine.setstate(gumballmachine.getsoldoutstate());
        }
    }
    
}