状态模式



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设计模式学习--状态模式（State Pattern）

概述

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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。

OO原则

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• 封装变化
• 多用组合，少用继承
• 针对接口编程，不针对实现编程
• 为交互对象之间的松耦合设计而努力
• 类应该对扩展开放，对修改关闭
• 依赖抽象，不要以来具体类
• 只和朋友交谈
• 别找我，我会找你
• 类应该只有一个改变的理由

要点

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• 状态模式允许一个对象基于内部状态而拥有不用的行为。
• 和程序状态机（PSM）不同，状态模式用类代表状态。
• Context会将行为委托给当前状态对象。
• 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。
• 状态模式和策略模式有相同的类图，但是它们的意图不同。
• 策略模式通常会用行为或算法来配置Context类。
• 状态模式允许Context随着状态的改变而改变行为。
• 状态转换可以由State类或Context类控制。
• 使用状态模式通常会导致设计中类的数目大量增加。
• 状态类可以被多个Context实例共享。

例子 糖果机

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先来看一下状态模式的类图

1. Context

定义客户感兴趣的接口。

维护一个ConcreteState子类的实例，这个实例定义当前状态。

GumballMachine.java

package gumballstate;

/**
 * 2013/7/12
 * @author wwj
 * 糖果机
 * 利用状态模式
 */
public class GumballMachine {

    State soldOutState;         //售空状态
    State noQuarterState;       //没有投入25分钱
    State hasQuarterState;      //有25分钱了
    State soldState;            //出售状态
    State winnerState;          //10%的中奖率

    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);
        winnerState = new WinnerState(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;
    }



    public State getState() {
        return state;
    }


    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 int getCount() {
        return count;
    }


    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();
    }

}

package gumballstate;

/**
 * 2013/7/12
 * @author wwj
 * 糖果机
 * 利用状态模式
 */
public class GumballMachine {
	
	State soldOutState;			//售空状态
	State noQuarterState;		//没有投入25分钱
	State hasQuarterState;		//有25分钱了
	State soldState;			//出售状态
	State winnerState;			//10%的中奖率
	
	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);
		winnerState = new WinnerState(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;
	}
	
	
	
	public State getState() {
		return state;
	}


	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 int getCount() {
		return count;
	}


	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();
	}
	
}

2.State

定义一个接口以封装与Context的一个特定状态相关的行为。

State.java

package gumballstate;

/**
 * 状态接口
 * @author wwj
 *
 */
public interface State {
    void insertQuarter();
    void ejectQuarter();
    void turnCrank();
    void dispense();
}

package gumballstate;

/**
 * 状态接口
 * @author wwj
 *
 */
public interface State {
	void insertQuarter();
	void ejectQuarter();
	void turnCrank();
	void dispense();
}

3.ConcreteStateSubClasses

每一个子类实现与context的一个状态相关的行为

NoQuarterState.java

package gumballstate;


/**
 * 2013/7/12
 * @author wwj
 * 实现状态接口状态类：没有25分钱
 */
public class NoQuarterState implements State {
    GumballMachine gumballMachine;

    public NoQuarterState(GumballMachine gumballMachine2) {
        this.gumballMachine = gumballMachine2;
    }

    @Override
    public void insertQuarter() {       //如果有人投入了25分钱，就将状态转换为HasQuarterState
        System.out.println("You inserted a quarter");
    }

    @Override
    public void ejectQuarter() {        //如果没给钱，就不能要求退钱
        System.out.println("You haven't inserted a quarter");
    }

    @Override
    public void turnCrank() {       //如果没给钱，就不能要求糖果
        System.out.println("You turned, but there's no quarter");
    }

    @Override
    public void dispense() {        //如果没得到钱，我们就不能发放糖果
        System.out.println("You need to pay first");
    }

}

package gumballstate;


/**
 * 2013/7/12
 * @author wwj
 * 实现状态接口状态类：没有25分钱
 */
public class NoQuarterState implements State {
	GumballMachine gumballMachine;
	
	public NoQuarterState(GumballMachine gumballMachine2) {
		this.gumballMachine = gumballMachine2;
	}

	@Override
	public void insertQuarter() {		//如果有人投入了25分钱，就将状态转换为HasQuarterState
		System.out.println("You inserted a quarter");
	}

	@Override
	public void ejectQuarter() {		//如果没给钱，就不能要求退钱
		System.out.println("You haven't inserted a quarter");
	}

	@Override
	public void turnCrank() {		//如果没给钱，就不能要求糖果
		System.out.println("You turned, but there's no quarter");
	}

	@Override
	public void dispense() {		//如果没得到钱，我们就不能发放糖果
		System.out.println("You need to pay first");
	}

}

HasQuarterState.java

package gumballstate;

import java.util.Random;

public class HasQuarterState implements State {
    Random randomWinner = new Random(System.currentTimeMillis());   //随机数产生器
    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...");
        int winner = randomWinner.nextInt(10);  //参数0~10的随机数
        if((winner == 0) && (gumballMachine.getCount() > 1)) {   //如果随机树为0，且足够的糖果的话，则可以得到两颗糖果
            gumballMachine.setState(gumballMachine.getWinnerState());
        } else {
            gumballMachine.setState(gumballMachine.getSoldState());
        }
    }

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

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

package gumballstate;

import java.util.Random;

public class HasQuarterState implements State {
	Random randomWinner = new Random(System.currentTimeMillis());	//随机数产生器
	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...");
		int winner = randomWinner.nextInt(10);	//参数0~10的随机数
		if((winner == 0) && (gumballMachine.getCount() > 1)) {	//如果随机树为0，且足够的糖果的话，则可以得到两颗糖果
			gumballMachine.setState(gumballMachine.getWinnerState());
		} else {
			gumballMachine.setState(gumballMachine.getSoldState());
		}
	}

    public void dispense() {
        System.out.println("No gumball dispensed");
    }
 
	public String toString() {
		return "waiting for turn of crank";
	}
}

SoldState.java

package 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";
    }
}

package 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";
	}
}

SoldOutState.java

package 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";
    }
}

package 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";
	}
}

WinnerState.java

package gumballstate;

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("Please wait, we're already giving you a Gumball");
    }

    public void turnCrank() {
        System.out.println("Turning again 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());
            }
        }
    }

    public String toString() {
        return "despensing two gumballs for your quarter, because YOU'RE A WINNER!";
    }
}

package gumballstate;

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("Please wait, we're already giving you a Gumball");
	}
 
	public void turnCrank() {
		System.out.println("Turning again 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());
			}
		}
	}
 
	public String toString() {
		return "despensing two gumballs for your quarter, because YOU'RE A WINNER!";
	}
}

测试

package gumballstate;

public class GumballMachineTestDrive {

    public static void main(String[] args) {
        GumballMachine gumballMachine =
            new GumballMachine(10);

        System.out.println(gumballMachine);

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

        System.out.println(gumballMachine);

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

        System.out.println(gumballMachine);

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

        System.out.println(gumballMachine);

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

        System.out.println(gumballMachine);

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

        System.out.println(gumballMachine);
    }
}

package gumballstate;

public class GumballMachineTestDrive {

	public static void main(String[] args) {
		GumballMachine gumballMachine = 
			new GumballMachine(10);

		System.out.println(gumballMachine);

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

		System.out.println(gumballMachine);

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

		System.out.println(gumballMachine);

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

		System.out.println(gumballMachine);

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

		System.out.println(gumballMachine);

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

		System.out.println(gumballMachine);
	}
}

Mighty Gumball, Inc.
Java-enabled Standing Gumball Model #2004
Inventory: 10 gumballs
Machine is waiting for quarter


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...


Mighty Gumball, Inc.
Java-enabled Standing Gumball Model #2004
Inventory: 8 gumballs
Machine is waiting for quarter


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...


Mighty Gumball, Inc.
Java-enabled Standing Gumball Model #2004
Inventory: 6 gumballs
Machine is waiting for quarter


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...


Mighty Gumball, Inc.
Java-enabled Standing Gumball Model #2004
Inventory: 4 gumballs
Machine is waiting for quarter


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...


Mighty Gumball, Inc.
Java-enabled Standing Gumball Model #2004
Inventory: 2 gumballs
Machine is waiting for quarter


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...
Oops, out of gumballs!


Mighty Gumball, Inc.
Java-enabled Standing Gumball Model #2004
Inventory: 0 gumballs
Machine is sold out