设计模式之状态模式

情景：有一个自动投币的糖果机。它有以下几种状态（每个圆圈代表一个状态）：

如果用常量值来定义几个变量

SOLD_OUT = 0 NO_QUARTER = 1 HAS_QUARTER = 2 SOLD = 3int state = SOLD_OUT;

这样状态变化就可以写成：

(state == (state ==

每一个动作都要先判断状态，改后再决定反馈以及下一个状态是什么。

虽然可以实现要求，但是当出现新的状态的时候，很不利于扩展。

我们把状态变成一个类，把不同的状态封装在各自的类中，然后在动作发生时委托给当前状态。

首先，定义状态接口

然后定义各种状态

NoQuarterState

GumballMachine gumballMachine;

</span><span style="color: #0000ff;"&gt;public</span><span style="color: #000000;"&gt; NoQuarterState(GumballMachine gumballMachine) {
    </span><span style="color: #0000ff;"&gt;this</span>.gumballMachine =<span style="color: #000000;"&gt; gumballMachine; 
}

@Override
</span><span style="color: #0000ff;"&gt;public</span> <span style="color: #0000ff;"&gt;void</span><span style="color: #000000;"&gt; insertQuarter() {
    System.out.println(</span>"You insert a quarter"<span style="color: #000000;"&gt;);
    gumballMachine.setState(gumballMachine.getHasQuarterState());
}

@Override
</span><span style="color: #0000ff;"&gt;public</span> <span style="color: #0000ff;"&gt;void</span><span style="color: #000000;"&gt; ejectQuarter() {
    System.out.println(</span>"You haven't inserted a quarter"<span style="color: #000000;"&gt;);
}

@Override
</span><span style="color: #0000ff;"&gt;public</span> <span style="color: #0000ff;"&gt;void</span><span style="color: #000000;"&gt; turnCrank() {
    System.out.println(</span>"You turned,but there's no quarter"<span style="color: #000000;"&gt;);
}

@Override
</span><span style="color: #0000ff;"&gt;public</span> <span style="color: #0000ff;"&gt;void</span><span style="color: #000000;"&gt; dispense() {
    System.out.println(</span>"You need to pay first"<span style="color: #000000;"&gt;);
}

}

HasQuarterState GumballMachine gumballMachine; public HasQuarterState(GumballMachine gumballMachine) { this.gumballMachine = gumballMachine; } @Override public void insertQuarter() { System.out.println("You can't insert another quater"); } @Override public void ejectQuarter() { System.out.println("Quarter returned"); gumballMachine.setState(gumballMachine.getNoQuarterState()); } @Override public void turnCrank() { System.out.println("You turned..."); gumballMachine.setState(gumballMachine.getSoldState()); } @Override public void dispense() { System.out.println("No gumball dispensed"); }

SoldOutState GumballMachine gumballMachine; public SoldOutState(GumballMachine gumballMachine) { this.gumballMachine = gumballMachine; } @Override public void insertQuarter() { System.out.println("You can't insert a quarter,the machine is sold out"); } @Override public void ejectQuarter() { System.out.println("You can't eject,you haven't inserted a quarter yet"); } @Override public void turnCrank() { System.out.println("You turned,but there are no gumballs"); } @Override public void dispense() { System.out.println("No gumball dispensed"); }

SoldState GumballMachine gumballMachine; public SoldState(GumballMachine gumballMachine) { this.gumballMachine = gumballMachine; } @Override public void insertQuarter() { System.out.println("Please wait,we're already giving you a gumball"); } @Override public void ejectQuarter() { System.out.println("Sorry,you already turned the crank"); } @Override public void turnCrank() { System.out.println("Turning twice doesn't get you another gumball!"); } @Override 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()); } }

设计模式之状态模式

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