JAVA编程思想第十九章练习题

public class E01 {
    Signal color = Signal.RED;
    public void change(){
        switch (color){
            case RED: color = Signal.GREEN;
            break;
            case GREEN: color = Signal.YELLOW;
            break;
            case YELLOW:color = Signal.RED;
        }
    }

    @Override
    public String toString() {
        return "The traffic light is "+ color;
    }

    public static void main(String[] args) {
        E01 t = new E01();
        for (int i = 0; i < 7; i++) {
            System.out.println(t);
            t.change();
        }
    }
}

 练习3：

package menu;

public interface Food {
    enum Appetizer implements Food{
        SALAD, SOUP, SPRING_ROLLS;
    }
    enum Beverage implements Food{
        BEER,VINE,JUICE,COLA,WATER;
    }
    enum MainCourse implements Food {
        LASAGNE, BURRITO, PAD_THAI,
        LENTILS, HUMMOUS, VINDALOO;
    }
    enum Dessert implements Food {
        TIRAMISU, GELATO, BLACK_FOREST_CAKE,
        FRUIT, CREME_CARAMEL;
    }
    enum Coffee implements Food {
        BLACK_COFFEE, DECAF_COFFEE, ESPRESSO,
        LATTE, CAPPUCCINO, TEA, HERB_TEA;
    }
}