在UML当中有状态机视图，这个状态机可以用于自动售货机，自动售票机等等场景，下面是用java代码模拟的一个状态机：

1.状态机接口

package stateMachine;  
/** 
 * 状态机接口 
 * @author seacean 
 * @date 2013-8-29 
 */  
public interface State {  
    /** 
     * 投入硬币 
     */  
    void insertQuarter();  
    /** 
     * 根据摇动情况，处理摇动结果，返回处理结果，释放糖果 
     */  
    void ejectQuarter();  
    /** 
     * 转动摇柄 
     */  
    void turnCrank();  
    /** 
     * 机器放出糖果，处理机器内部状态，返回初始可投币状态 
     */  
    void dispense();  
}  

2.带有状态机的机器

package stateMachine;  
/** 
 * 机器类，包含多种状态，处理流程 
 * @author seacean 
 * @date 2013-8-29 
 */  
public class Machine {  
    //机器本身包含所有的状态机  
    private State soldOutState;  
    private State noQuarterState;  
    private State hasQuarterState;  
    private State soldState;  
  
    private State state; //机器的当前状态  
    private int count = 0;//机器中当前糖果的数量  
    /** 
     * 初始化机器，引入所有的状态机，初始化糖果数量，初始化机器状态 
     * @param count 
     */  
    public Machine(int count) {  
        this.soldOutState = new SoldOutState(this);  
        this.noQuarterState = new NoQuarterState(this);  
        this.hasQuarterState = new HasQuarterState(this);  
        this.soldState = new SoldState(this);  
        this.count = count;  
        if (this.count > 0) {  
            this.state = noQuarterState;  
        }  
    }  
    /** 
     * 释放糖果时的内部处理程序 
     */  
    public void releaseBall() {  
        System.out.println("a gumball comes rolling out the solt...");  
        if (count > 0) {  
            count -= 1;  
        }  
    }  
      
    public void insertQuerter() {  
        state.insertQuarter();//加入硬币  
    }  
  
    public void ejectQuarter() {  
        state.ejectQuarter();  
    }  
  
    public void turnCrank() {  
        state.turnCrank();  
        state.dispense();  
    }  
  
    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;  
    }  
  
    public void setState(State state) {  
        this.state = state;  
    }  
}  

3.下面是状态机的一些实现类

package stateMachine;  
/** 
 * 机器处于没有投硬币的状态 
 * @author seacean 
 * @date 2013-8-29 
 */  
public class NoQuarterState implements State {  
    private Machine machine;  
  
    public NoQuarterState(Machine machine) {  
        this.machine = machine;  
    }  
  
    @Override  
    public void insertQuarter() {  
        System.out.println("please insert a quarter!");  
        machine.setState(machine.getHasQuarterState());  
    }  
  
    @Override  
    public void ejectQuarter() {  
        System.out.println("please insert a quarter!");  
    }  
  
    @Override  
    public void turnCrank() {  
        System.out.println("please insert a quarter!");  
    }  
  
    @Override  
    public void dispense() {  
        System.out.println("please insert a quarter!");  
    }  
  
}  

package stateMachine;  
/** 
 * 机器处于有硬币，有糖果，没有摇动的状态 
 * @author seacean 
 * @date 2013-8-29 
 */  
public class HasQuarterState implements State {  
    private Machine machine;  
      
    public HasQuarterState(Machine machine){  
        this.machine=machine;  
    }  
    @Override  
    public void insertQuarter() {  
        System.out.println("You can not insert another quarter!");  
    }  
  
    @Override  
    public void ejectQuarter() {  
        System.out.println("Quarter returned!");  
        machine.setState(machine.getNoQuarterState());  
    }  
  
    @Override  
    public void turnCrank() {  
        System.out.println("You turned ... ");  
        machine.setState(machine.getSoldState());  
    }  
  
    @Override  
    public void dispense() {  
        System.out.println("No gumball dispensed!");  
    }  
  
}  

package stateMachine;  
  
/** 
 * 机器正在出售糖果的状态 
 *  
 * @author seacean 
 * @date 2013-8-29 
 */  
public class SoldState implements State {  
    private Machine machine;  
  
    public SoldState(Machine machine) {  
        this.machine = machine;  
    }  
  
    @Override  
    public void insertQuarter() {  
        System.out.println("please wait,we are already giving you a gumball!");  
    }  
  
    @Override  
    public void ejectQuarter() {  
        System.out.println("Sorry, you have turned the crank!");  
    }  
  
    @Override  
    public void turnCrank() {  
        System.out.println("Turning twice does not get you another gumball!");  
    }  
  
    @Override  
    public void dispense() {  
        machine.releaseBall();  
        if (machine.getCount() > 0) {  
            machine.setState(machine.getNoQuarterState());  
        } else {  
            System.out.println("Out of Gumballs!");  
            machine.setState(machine.getSoldOutState());  
        }  
    }  
  
}  

package stateMachine;  
/** 
 * 机器处于无糖果状态 
 * @author seacean 
 * @date 2013-8-29 
 */  
public class SoldOutState implements State {  
    private Machine machine;  
    public SoldOutState(Machine machine) {  
        this.machine=machine;  
    }  
  
    @Override  
    public void insertQuarter() {  
        System.out.println("Sorry, there is no gumball in the machine!");  
    }  
  
    @Override  
    public void ejectQuarter() {  
        System.out.println("Sorry, there is no gumball in sold!");  
    }  
  
    @Override  
    public void turnCrank() {  
        System.out.println("Sorry, there is no gumball!Turn is no meaning.");  
        machine.setState(machine.getNoQuarterState());  
    }  
  
    @Override  
    public void dispense() {  
        System.out.println("Sorry, there is no gumball!");  
    }  
  
}  

4.下面是测试类

package stateMachine;  
//测试类  
public class StateMachineTest {  
    public static void main(String[] args) {  
         Machine machine=new Machine(10);  
         for(int i=0;i<11;i++){ system.out.println(machine);="" machine.insertquerter();="" machine.turncrank();="" }="" <="" code="">