深入浅出设计模式十二－状态模式(行为型)

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.

UML图

UML解析:

 示例程序:

如上面所示,我们有四个不同的状态,以及四个不同的操作,每个操作都可能改变状态.

运用状态模式代码如下:

package com.lwf.state;

public interface State {

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

package com.lwf.state;

public class NoQuarterState implements State{

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

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

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

	@Override
	public void turnCrank() {
		System.out.println("You turned ,but no quarter");
		
	}
	
	@Override
	public void dispense() {
		System.out.println("No money ,Pay first!");
	}

}

package com.lwf.state;

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

	@Override
	public void ejectQuarter() {
		System.out.println("Quarter returned");
		gumballMachine.setState(gumballMachine.getNoQuarterState());
	}

	@Override
	public void insertQuarter() {
		System.out.println("Have inserted already,Coudn't insert again");
	}

	@Override
	public void turnCrank() {
		System.out.println("You turned");
		gumballMachine.setState(gumballMachine.getSoldState());
	}

	@Override
	public void dispense() {
		System.out.println("you state not permit this action");

	}
}

package com.lwf.state;

public class SoldState implements State {

	GumballMachine gumballMachine ;
	
	public SoldState(GumballMachine gumballMachine){
		this.gumballMachine = gumballMachine;
	}
	
	@Override
	public void dispense() {
		System.out.println("dispense....");
		gumballMachine.releaseBall();
		if(gumballMachine.count>0){
			gumballMachine.setState(gumballMachine.getNoQuarterState());
		}else{
			gumballMachine.setState(gumballMachine.getSoldOutState());
		}

	}

	@Override
	public void ejectQuarter() {
		System.out.println("you state not permit this action");
	}

	@Override
	public void insertQuarter() {
		System.out.println("you state not permit this action");

	}

	@Override
	public void turnCrank() {
		System.out.println("you state not permit this action");

	}

}

package com.lwf.state;

public class SoldOutState implements State {

	GumballMachine gumballMachine ;
	
	public SoldOutState(GumballMachine gumballMachine){
		this.gumballMachine = gumballMachine;
	}
	@Override
	public void dispense() {
		System.out.println("sold out");

	}

	@Override
	public void ejectQuarter() {
		System.out.println("sold out");
	}

	@Override
	public void insertQuarter() {
		System.out.println("sold out");
	}

	@Override
	public void turnCrank() {
		System.out.println("sold out");

	}

}

package com.lwf.state;

public class GumballMachine {

	State noQuarterState;
	State hasQuarterState;
	State soldState;
	State soldOutState;
	
	State state = soldOutState;
	int count = 0;
	public GumballMachine(int numberGumballs){
		noQuarterState = new NoQuarterState(this);
		hasQuarterState = new HasQuarterState(this);
		soldState = new SoldState(this);
		soldOutState = new SoldOutState(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();
	}
	
	public void setState(State state){
		this.state = state;
	}
	
	public void releaseBall(){
		
		if(count!=0){
			count = count -1;
		}
		System.out.println("release a Quarter,the Number left : " + count);
	}

	public State getNoQuarterState() {
		return noQuarterState;
	}

	public State getHasQuarterState() {
		return hasQuarterState;
	}

	public State getSoldState() {
		return soldState;
	}

	public State getSoldOutState() {
		return soldOutState;
	}

	public int getCount() {
		return count;
	}
	
	public static void main(String[] args) {
		GumballMachine g = new GumballMachine(10);
		g.insertQuarter();
		//g.ejectQuarter();
		g.turnCrank();
		
	}
}

运行GumballMachine类当插入一个25分钱后转动转轴, 售出糖果,数量减少一

结果:

You insert a Quarter
You turned
dispense....
release a Quarter,the Number left : 9

比较一下状态模式与策略模式我们发现它们的类图基本相同.它们的区别主要在使用它们的意图.