使用Enum的自动贩卖机
package enumerated;import java.util.EnumMap;import java.util.Iterator;import Container.Generator;import static enumerated.Input.*;enum Category{MONEY(NICKEL, DIME, QUARTER),TIME_SELECTION( CHIPS, SODA, SOAP),QUIT_TRANSACTION(ABORT_TRANSACTION),SHUT_DOWN(STOP);private Input[] values;Category(Input... types){values = types;}private static EnumMap<Input, Category> categories = new EnumMap<Input, Category>(Input.class);static{for(Category c : Category.class.getEnumConstants()){for(Input type : c.values){categories.put(type, c);}}}public static Category categorize(Input input){return categories.get(input);}}public class VendingMachine {private static State state = State.RESTING;private static int amount = 0;private static Input selection = null;enum StateDuration{TRANSIENT}enum State{RESTING{void next(Input input){switch(Category.categorize(input)){case MONEY:amount += input.amount();state = ADDING_MONEY;break;case SHUT_DOWN:state = TERMINAL;default:}}},ADDING_MONEY{void next(Input input){switch(Category.categorize(input)){case MONEY:amount += input.amount();break;case TIME_SELECTION:selection = input;if(amount < selection.amount())System.out.println("Insufficient money for "+selection);elsestate = DISPENSING;break;case QUIT_TRANSACTION:state = GIVING_CHANGE;break;case SHUT_DOWN:state = TERMINAL;default:}}},DISPENSING(StateDuration.TRANSIENT){void next(){System.out.println("hers is your "+selection);amount -= selection.amount();state = GIVING_CHANGE;}},GIVING_CHANGE(StateDuration.TRANSIENT){void next(){if(amount > 0){System.out.println("Your change: "+amount);amount = 0;}state = RESTING;}},TERMINAL{void output(){System.out.println("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(){System.out.println(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();if(args.length == 1){gen = new FileInputGenerator(args[0]);}run(gen);}}class RandomInputGenerator implements Generator<Input>{public Input next(){return Input.randomSelection();}}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());}}?
Category enum将不同类型的Input进行分组，因为可以使用categorize()方法为switch语句生成
恰当的Category实例。 使用EnumMap确保了查询时的效率和安全。
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?设计缺陷： 它要求 enum State实例访问的VendingMachine属性必须声明为static,这意味着，
只能有一个VendiingMachine实例(事实上够了，因为每台机，只有一个应该程序)。