public class GumballMachine { final static int SOLD_OUT = 0; final static int NO_QUARTER = 1; final static int HAS_QUARTER = 2; final static int SOLD = 3; //以上四个变量用来设计四个状态 int state = SOLD_OUT; //用来追踪当前状态 int count = 0; //用来保存糖果数量 public GumballMachine(int count) { this.count = count; if (count > 0) { state = NO_QUARTER; } } public void insertQuarter () { if (state = HAS_QUARTER) { System.out.println("You can't insert another quarter"); } else if (state = NO_QUARTER) { state = HAS_QUARTER; System.out.println("You inserted a aquarter"); } else if (state = SOLD_OUT) { System.out.println("You can't insert a quarter , the machine if sold out"); } else if (state = SOLD) { System.out.println("Please wait, we're already giving you'a gumball"); } } }
恕我直言,这个要求真的是无语,没办法,毕竟是需求方的要求,只能帮他们实现了,这个时候,就发现我们之前写的代码不怎么易于维护和修改了吧,这个时候我们就需要重新构造他了。
让我们实现上面这个模式吧。(这里的类图少了一个WinnerState类,就是成功的能有两颗糖,不要在意,我们会在下面的代码中实现的)
State类:
public interface State { public void insertQuarter(); public void ejectQuarter(); public void turnCrank(); public void dispense(); }
GumballMachine类:
public class GumballMachine { State soldOutState; State noQuarterState; State hasQuarterState; State soldState; State winnerState; //以上是所有的状态 State state = soldOutState; //追踪当前状态 int count = 0; //记录糖果数 public void insertQuarter() { state.insertQuarter(); } public void ejectQuarter() { state.ejectQuarter(); } public void turnCrank() { state.turnCrank(); state.dispense(); //我们不需要单独实现dispense方法,可以把这个方法写入turnCrank里面 } public void setState (State state) { this.state = state; } public void releaseBall() { System.out.println("A gumball comes rolling out the slot..."); if (count != 0) { count = count - 1; } } public State getSoldOutState() { return soldOutState; } public State getNoQuarterState() { return noQuarterState; } public State getHasQuarterState() { return hasQuarterState; } public State getSoldState() { return soldState; } public State getWinnerState() { return winnerState; } public State getState() { return state; } public int getCount() { return count; } }
HasQuarterState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"); } }
WinnerState类:
public class WinnerState implements State { GumballMachine gumballMachine; public WinnerState(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() { System.out.println("You're a winner ! you get two gumballs for your quarter"); gumballMachine.releaseBall(); if (gumballMachine.getCount() == 0) { gumballMachine.setState(gumballMachine.getSoldOutState()); } else { gumballMachine.releaseBall(); if (gumballMachine.getCount() > 0) { gumballMachine.setState(gumballMachine.getNoQuarterState()); } else { System.out.println("Oops, out of gumballs"); gumballMachine.setState(gumballMachine.getSoldOutState()); } } } }
定义状态模式:允许对象在内部状态改变时改变它的行为,对象看起来好像修改了它的类。
状态模式的类图:
总结:
1:状态模式允许一个对象基于内部状态而拥有不同的行为。
2:状态模式用类代表状态。
3:通过将每个状态封装进一个类,我们把以后需要做的任何改变局部化了。
4:状态模式和策略模式有相同的类图,但是他们的意图不一样。
5:使用状态模式通常会导致设计中类的数目大量增加。