每天学一点设计模式-状态模式

利用状态模式前我们的代码：

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;
	int state = SOLD_OUT;
	int count = 0;

	public GumballMachine(int count) {
		this.count = count;
		if (count > 0) {
			state = NO_QUARTER;
		}
	}

	// 投入钱
	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 quarter");
		} else if (state == SOLD_OUT) {
			System.out.println("the machine is sold out");
		} else if (state == SOLD) {
			System.out.println("please wait,Are Shopping");
		}
	}

	// 退钱
	public void ejectQuarter() {
		if (state == HAS_QUARTER) {
			System.out.println("quarter returned");
			state = NO_QUARTER;
		} else if (state == NO_QUARTER) {
			System.out.println("You haven't inserted a quarter");
		} else if (state == SOLD) {
			System.out.println("sorry,you already get a goods");
		} else if (state == SOLD_OUT) {
			System.out
					.println("you can't eject,you haven't insert a quarter yet");
		}
	}

	// 转动扭杆
	public void turnCrank() {
		if (state == SOLD) {
			System.out.println("you already get a goods");
		} else if (state == NO_QUARTER) {
			System.out.println("you don't insert Quarter");
		} else if (state == SOLD_OUT) {
			System.out.println("no goods now");
		} else if (state == HAS_QUARTER) {
			System.out.println("are shopping");
			state = SOLD;
			despense();
		}
	}

	private void despense() {
		if (state == SOLD) {
			System.out.println("A gumball comes rolling out the slot");
			count--;
			if (count == 0) {
				state = SOLD_OUT;
			} else {
				state = NO_QUARTER;
			}
		} else if (state == NO_QUARTER) {
			System.out.println("you don't insert Quarter");
		} else if (state == SOLD_OUT) {
			System.out.println("no goods dispensed");
		} else if (state == HAS_QUARTER) {
			System.out.println("no goods dispensed");
		}
	}

	@Override
	public String toString() {
		return "GumballMachine [state=" + state + ", count=" + count + "]";
	}
	
	
	
}

测试程序

public class GumballMachineTestDrive {

	public static void main(String[] args) {
		GumballMachine gumballMachine = new GumballMachine(5);
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.ejectQuarter();
		gumballMachine.turnCrank();
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.ejectQuarter();
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		System.out.println(gumballMachine);
	}
}

输出

GumballMachine [state=1, count=5]
You inserted a quarter
are shopping
A gumball comes rolling out the slot
GumballMachine [state=1, count=4]
You inserted a quarter
quarter returned
you don't insert Quarter
GumballMachine [state=1, count=4]
You inserted a quarter
are shopping
A gumball comes rolling out the slot
You inserted a quarter
are shopping
A gumball comes rolling out the slot
You haven't inserted a quarter
GumballMachine [state=1, count=2]
You inserted a quarter
You can't insert another quarter
are shopping
A gumball comes rolling out the slot
You inserted a quarter
are shopping
A gumball comes rolling out the slot
the machine is sold out
no goods now
GumballMachine [state=0, count=0]

利用状态模式后代码变为如下形式

状态接口state

public interface State {
	void insertQuarter();

	void ejectQuarter();

	void turnCrank();

	void dispense();
}

各种状态实现

public class NoQuarterState implements State {
	GumballMachine gumballMachine;

	public NoQuarterState(GumballMachine gumballMachine) {
		this.gumballMachine = gumballMachine;
	}

	@Override
	public void insertQuarter() {
		System.out.println("You inserted a quarter!");
		gumballMachine.setState(gumballMachine.getHasQuarterState());
	}

	@Override
	public void ejectQuarter() {
		System.out.println("You haven't inserted a quarter");

	}

	@Override
	public void turnCrank() {
		System.out.println("You turned ,but there's no quarter");

	}

	@Override
	public void dispense() {
		System.out.println("You need to pay first");

	}

}

public class HasQuarterState implements State {
	GumballMachine gumballMachine;

	public HasQuarterState(GumballMachine gumballMachine) {
		this.gumballMachine = gumballMachine;
	}

	@Override
	public void insertQuarter() {
		System.out.println("Has Quarter,can't insert again!");
	}

	@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!");

	}

}

public class SoldOutState implements State {
	GumballMachine gumballMachine;

	public SoldOutState(GumballMachine gumballMachine) {
		this.gumballMachine = gumballMachine;
	}

	@Override
	public void insertQuarter() {
		System.out.println("sorry,gumball has sold out!");

	}

	@Override
	public void ejectQuarter() {
		// TODO Auto-generated method stub
		System.out
				.println("sorry,you don't insert quarter,but gumball has sold out!");
	}

	@Override
	public void turnCrank() {
		// TODO Auto-generated method stub
		System.out
				.println("sorry,you don't insert quarter,but gumball has sold out!");
	}

	@Override
	public void dispense() {
		System.out.println("sorry,gumball has sold out!");
	}

}

public class SoldState implements State {
	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 alread 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 {
			gumballMachine.setState(gumballMachine.getSoldOutState());
		}

	}

}

存放状态的对象

public class GumballMachine {
	State soldOutState;
	State noQuarterState;
	State hasQuarterState;
	State soldState;

	State state = soldOutState;
	int count = 0;

	public GumballMachine(int count) {
		soldOutState = new SoldOutState(this);
		noQuarterState = new NoQuarterState(this);
		hasQuarterState = new HasQuarterState(this);
		soldState = new SoldState(this);
		this.count = count;
		if (count > 0) {
			state = noQuarterState;
		}
	}

	public void insertQuarter() {
		state.insertQuarter();
	}

	public void ejectQuarter() {
		// TODO Auto-generated method stub
		state.ejectQuarter();
	}

	public void turnCrank() {
		// TODO Auto-generated method stub
		state.turnCrank();
		state.dispense();
	}

	void setState(State state) {
		this.state = state;
	}

	void releaseBall() {
		System.out.println("A gumball comes rolling out the slot ...");
		if (count != 0) {
			--count;
		}
	}

	public State getSoldOutState() {
		return soldOutState;
	}

	public State getNoQuarterState() {
		return noQuarterState;
	}

	public State getHasQuarterState() {
		return hasQuarterState;
	}

	public State getSoldState() {
		return soldState;
	}
	
	public int getCount() {
		return count;
	}

	@Override
	public String toString() {
		return "GumballMachine [count=" + count + "]";
	}

}

测试程序不变，还是之前的测试程序

public class GumballMachineTestDrive {

	public static void main(String[] args) {
		GumballMachine gumballMachine = new GumballMachine(5);
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.ejectQuarter();
		gumballMachine.turnCrank();
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.ejectQuarter();
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		System.out.println(gumballMachine);
	}
}

结果

GumballMachine [count=5]
You inserted a quarter!
You turned...
A gumball comes rolling out the slot ...
GumballMachine [count=4]
You inserted a quarter!
quarter returned
You turned ,but there's no quarter
You need to pay first
GumballMachine [count=4]
You inserted a quarter!
You turned...
A gumball comes rolling out the slot ...
You inserted a quarter!
You turned...
A gumball comes rolling out the slot ...
You haven't inserted a quarter
GumballMachine [count=2]
You inserted a quarter!
Has Quarter,can't insert again!
You turned...
A gumball comes rolling out the slot ...
You inserted a quarter!
You turned...
A gumball comes rolling out the slot ...
sorry,gumball has sold out!
sorry,you don't insert quarter,but gumball has sold out!
sorry,gumball has sold out!
GumballMachine [count=0]

状态模式

英文名

State Pattern

定义

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。