設計模式讀書筆記-2狀態模式State

[b]1.定義[/b]
當一個對象的內在狀態改變時允許改變其行爲，這個對象看起來像是改變了其類。

[b]2.類圖[/b]
[img]http://dl.iteye.com/upload/picture/pic/105526/769a3ba4-0622-32a0-bf5a-557b09f1fb11.png[/img]

[b]3.實例[/b]
State

package headfirst.state.gumballstate;

public interface State {

	public void insertQuarter();
	public void ejectQuarter();
	public void turnCrank();
	public void dispense();
}

HasQuarterState

package headfirst.state.gumballstate;


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 String toString() {
		return "waiting for turn of crank";
	}
}

NoQuarterState

package headfirst.state.gumballstate;

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");
	} 

	public String toString() {
		return "waiting for quarter";
	}
}

SoldOutState

package headfirst.state.gumballstate;

public class SoldOutState implements State {
    GumballMachine gumballMachine;

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

	public void insertQuarter() {
		System.out.println("You can't insert a quarter, the machine is sold out");
	}

	public void ejectQuarter() {
		System.out.println("You can't eject, you haven't inserted a quarter yet");
	}

	public void turnCrank() {
		System.out.println("You turned, but there are no gumballs");
	}

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

	public String toString() {
		return "sold out";
	}
}

SoldState

package headfirst.state.gumballstate;

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());
		}
	}

	public String toString() {
		return "dispensing a gumball";
	}
}

GumballMachine

package headfirst.state.gumballstate;

public class GumballMachine {

	State soldOutState;
	State noQuarterState;
	State hasQuarterState;
	State soldState;

	State state = soldOutState;
	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;
		} 
	}

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

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

	public void turnCrank() {
		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 = count - 1;
		}
	}

	int getCount() {
		return count;
	}

	void refill(int count) {
		this.count = count;
		state = noQuarterState;
	}

    public State getState() {
        return state;
    }

    public State getSoldOutState() {
        return soldOutState;
    }

    public State getNoQuarterState() {
        return noQuarterState;
    }

    public State getHasQuarterState() {
        return hasQuarterState;
    }

    public State getSoldState() {
        return soldState;
    }

	public String toString() {
		StringBuffer result = new StringBuffer();
		result.append("\nMighty Gumball, Inc.");
		result.append("\nJava-enabled Standing Gumball Model #2004");
		result.append("\nInventory: " + count + " gumball");
		if (count != 1) {
			result.append("s");
		}
		result.append("\n");
		result.append("Machine is " + state + "\n");
		return result.toString();
	}
}

GumballMachineTestDrive

package headfirst.state.gumballstate;

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.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();

		System.out.println(gumballMachine);
	}
}