先是输入的枚举类型

public enum Input {
  NICKEL(5), DIME(10), QUARTER(25), DOLLAR(100),
  TOOTHPASTE(200), CHIPS(75), SODA(100), SOAP(50),
  ABORT_TRANSACTION {
    public int amount() { // Disallow
      throw new RuntimeException("ABORT.amount()");
    }
  },
  STOP { // This must be the last instance.
    public int amount() { // Disallow
      throw new RuntimeException("SHUT_DOWN.amount()");
    }
  };    
  int value; // In cents
  Input(int value) { this.value = value; }
  Input() {}
  int amount() { return value; }; // In cents
  static Random rand = new Random(47);
  public static Input randomSelection() {
    // Don't include STOP:
    return values()[rand.nextInt(values().length - 1)];
  }
} 

分析里面的values都是NICKEL(5), DIME(10), QUARTER(25), DOLLAR(100),
TOOTHPASTE(200), CHIPS(75), SODA(100), SOAP(50)
代表的钱的面值和商品的价格
randomSelection()方法随机输出一个values数组中的值除了STOP；

enum Category {
  MONEY(NICKEL, DIME, QUARTER, DOLLAR),
  ITEM_SELECTION(TOOTHPASTE, CHIPS, SODA, SOAP),
  QUIT_TRANSACTION(ABORT_TRANSACTION),
  SHUT_DOWN(STOP);
 //Input.values
  private Input[] values;
  Category(Input... types) { values = types; }  
  private static EnumMap<Input,Category> categories =
    new EnumMap<Input,Category>(Input.class);
  //将enum赋值给c 将Input 和c加入EnumMap
  static {
    for(Category c : Category.class.getEnumConstants())
      for(Input type : c.values)
        categories.put(type, c);
  }
  //返回c.values的值
  public static Category categorize(Input input) {
    return categories.get(input);
  }
}   

public class VendingMachine {
    //state是状态
  private static State state = State.RESTING;
  //加入自动贩卖机的钱
  private static int amount = 0;
  private static Input selection = null;
  enum StateDuration { TRANSIENT } // Tagging enum
  enum State {
      //初始状态
    RESTING {
      void next(Input input) {
        switch(Category.categorize(input)) {
          case MONEY:
            amount += input.amount();
            print("amount"+amount);
            state = ADDING_MONEY;
            break;
          case SHUT_DOWN:
            state = TERMINAL;
          default:
        }
      }
    },  
    //价钱到贩卖机
    ADDING_MONEY {
      void next(Input input) {
        switch(Category.categorize(input)) {
          case MONEY:
            amount += input.amount();
            break;
            //选择商品
          case ITEM_SELECTION:
            selection = input;
            if(amount < selection.amount())
              print("Insufficient money for " + selection);
            else state = DISPENSING;
            break;
          case QUIT_TRANSACTION:
            state = GIVING_CHANGE;
            break;
          case SHUT_DOWN:
            state = TERMINAL;
          default:
        }
      }
    },  
    //出商品
    DISPENSING(StateDuration.TRANSIENT) {
      void next() {
        print("here is your " + selection);
        amount -= selection.amount();
        state = GIVING_CHANGE;
      }
    },
    //找钱
    GIVING_CHANGE(StateDuration.TRANSIENT) {
      void next() {
        if(amount > 0) {
          print("Your change: " + amount);
          amount = 0;
        }
        state = RESTING;
      }
    },  
    //终端
    TERMINAL { void output() { print("Halted"); } };
    private boolean isTransient = false;
    State() {}
    State(StateDuration trans) { isTransient = true; }
    void next(Input input) {
      throw new RuntimeException("Only call " +
        "next(Input input) for non-transient states");
    }
    void next() {
      throw new RuntimeException("Only call next() for " +
        "StateDuration.TRANSIENT states");
    }
    void output() { print(amount); }
  } 
  static void run(Generator<Input> gen) {
    while(state != State.TERMINAL) {
      state.next(gen.next());
      while(state.isTransient)
        state.next();
      state.output();
    }
  }
  public static void main(String[] args) {
    Generator<Input> gen = new RandomInputGenerator();
    //判断从哪里输入
    if(args.length == 1)
      gen = new FileInputGenerator(args[0]);
      运行
    run(gen);
  }
}   

//输入Input
class RandomInputGenerator implements Generator<Input> {
  public Input next() { return Input.randomSelection(); }
}

//文件输入
class FileInputGenerator implements Generator<Input> {
  private Iterator<String> input;
  public FileInputGenerator(String fileName) {
    input = new TextFile(fileName, ";").iterator();
  }
  public Input next() {
    if(!input.hasNext())
      return null;
    return Enum.valueOf(Input.class, input.next().trim());
  }
}

在看程序执行的过程RandomInputGenerator或者FileInputGenerator输入Input，
判断从哪里输入 执行run。
run方法，判断是否为Transient。若为Transient，异常，输出剩余的amount（钱）
新手：欢迎指正