design pattern——状态模式

 

针对问题：有时候一个方法可能有很多if..else来判断状态后再执行相关操作，当很多方法都重复的出现这样的if..else判断时，就可以考虑用状态模式了。

      状态模式的结构图和策略模式一样，事实上状态模式和策略很相似，不同的是状态模式除了委托状态外，状态实体自身持有主实体对象的引用，在状态实体内部可以动态的改变主实体的状态。

 

 

 

 

状态模式结构图：

 

 

 

 

状态模式实现代码：

 

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





/**
 * 有钱状态
 * @author bruce
 *
 */
public class HasQuarterState implements State{
	
	GumballMachine gumballMachine;
	
	public HasQuarterState(GumballMachine gumballMachine){
		this.gumballMachine=gumballMachine;
	}

	public void dispense() {
		// TODO Auto-generated method stub
		System.out.println("No gumball dispensed");
	}

	public void ejectQuarter() {
		// TODO Auto-generated method stub
		System.out.println("Quarter returned");
		gumballMachine.setState(gumballMachine.getNoQuarterState());
	}

	public void insertQuarter() {
		// TODO Auto-generated method stub
		System.out.println("You can't insert another quarter");
	}

	public void turnCrank() {
		// TODO Auto-generated method stub
		System.out.println("You returned...");
		gumballMachine.setState(gumballMachine.getSoldState());
	}

}






/**
 * 没钱状态
 * @author bruce
 *
 */
public class NoQuarterState implements State{
	
	private GumballMachine gumballMachine;
	
	public NoQuarterState(GumballMachine gumballMachine){
		this.gumballMachine=gumballMachine;
	}

	public void dispense() {
		// TODO Auto-generated method stub
		System.out.println("You need to pay first");
	}

	public void ejectQuarter() {
		// TODO Auto-generated method stub
		System.out.println("You haven't inserted a quarter");
	}

	public void insertQuarter() {
		// TODO Auto-generated method stub
		System.out.println("You inserted a quarter");
		gumballMachine.setState(gumballMachine.getHasQuarterState());
	}

	public void turnCrank() {
		// TODO Auto-generated method stub
		System.out.println("You turned,but there's no quarter");
	}

}





/**
 * 售出状态
 * @author bruce
 *
 */
public class SoldState implements State{
	
	private GumballMachine gumballMachine;
	
	public SoldState(GumballMachine gumballMachine){
		this.gumballMachine=gumballMachine;
	}

	public void dispense() {
		// TODO Auto-generated method stub
		gumballMachine.releaseBall();
		if(gumballMachine.getCount()>0){
			gumballMachine.setState(gumballMachine.getNoQuarterState());
		}else{
			System.out.println("Oops,out of gumballs!");
			gumballMachine.setState(gumballMachine.getSoldOutState());
		}
	}

	public void ejectQuarter() {
		// TODO Auto-generated method stub
		System.out.println("Sorry, you already turned the crank");
	}

	public void insertQuarter() {
		// TODO Auto-generated method stub
		System.out.println("Please wait, we're already giving you a gumball");
	}

	public void turnCrank() {
		// TODO Auto-generated method stub
		System.out.println("Turning twice doesn't get you another gumball!");
	}

}





/**
 * 卖完状态
 * @author bruce
 *
 */
public class SoldOutState implements State{
	
	@SuppressWarnings("unused")
	private GumballMachine gumballMachine;
	
	public SoldOutState(GumballMachine gumballMachine){
		this.gumballMachine=gumballMachine;
	}

	public void dispense() {
		// TODO Auto-generated method stub
		System.out.println("No gumball dispensed");
	}

	public void ejectQuarter() {
		// TODO Auto-generated method stub
		System.out.println("You can't eject, you haven't inserted a quarter yet");
	}

	public void insertQuarter() {
		// TODO Auto-generated method stub
		System.out.println("You can't insert a quarter,the machine is sold out");
	}

	public void turnCrank() {
		// TODO Auto-generated method stub
		System.out.println("You turned, but there are no gumballs");
	}

}




/**
 * 糖果机
 * @author bruce
 *
 */
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;
		}
	}

	public State getSoldOutState() {
		return soldOutState;
	}

	public State getNoQuarterState() {
		return noQuarterState;
	}

	public State getHasQuarterState() {
		return hasQuarterState;
	}

	public State getSoldState() {
		return soldState;
	}

	public State getState() {
		return state;
	}

	public int getCount() {
		return count;
	}
	
	
}






/**
 * 测试
 * @author bruce
 *
 */
public class Client {
	
	public static void main(String[] args) {
		GumballMachine gumballMachine=new GumballMachine(5);
		
		System.out.println("-------------");
		
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		
		System.out.println("-------------");
		
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		
		System.out.println("-------------");
		
		
		/**
		 * output:
		 *  -------------
			You inserted a quarter
			You returned...
			A gumball comes rolling out the slot...
			-------------
			You inserted a quarter
			You returned...
			A gumball comes rolling out the slot...
			You inserted a quarter
			You returned...
			A gumball comes rolling out the slot...
			-------------
		 */
	}
}