Enum、EnumMap、EnumSet

一、Enum

• 不帶參數

public enum Car {  
    AUDI {  
        @Override  
        public int getPrice() {  
            return 25000;  
        }  
    },  
    MERCEDES {  
        @Override  
        public int getPrice() {  
            return 30000;  
        }  
    },  
    BMW {  
        @Override  
        public int getPrice() {  
            return 20000;  
        }  
    };  
      
    public abstract int getPrice();  
}

• 帶參數

// Create an EnumMap that contains all constants of the Car enum.  
        EnumMap cars = new EnumMap(Car.class);  
          
        // Put some values in the EnumMap.  
        cars.put(Car.BMW, Car.BMW.getPrice());  
        cars.put(Car.AUDI, Car.AUDI.getPrice());  
        cars.put(Car.MERCEDES, Car.MERCEDES.getPrice());  
          
        // Print the values of an EnumMap.  
        for(Car c: cars.keySet())  
            System.out.println(c.name());  
          
        System.out.println(cars.size());  
          
        // Remove a Day object.  
        cars.remove(Car.BMW);  
        System.out.println("After removing Car.BMW, size: " + cars.size());  
          
        // Insert a Day object.  
        cars.put(Car.valueOf("BMW"), Car.BMW.getPrice());  
        System.out.println("Size is now: " + cars.size());

二、EnumMap 

EnumMap cars = new EnumMap(Car.class);  
          
        // Put some values in the EnumMap.  
        cars.put(Car.BMW, Car.BMW.getPrice());  
        cars.put(Car.AUDI, Car.AUDI.getPrice());  
        cars.put(Car.MERCEDES, Car.MERCEDES.getPrice());

三、EnumSet

// Create an EnumSet that contains all days of the week.  
        EnumSet week = EnumSet.allOf(Day.class);  
          
        // Print the values of an EnumSet.  
        for(Day d: week)  
            System.out.println(d.name());  
          
        System.out.println(week.size());  
          
        // Remove a Day object.  
        week.remove(Day.FRIDAY);  
        System.out.println("After removing Day.FRIDAY, size: " + week.size());  
          
        // Insert a Day object.  
        week.add(Day.valueOf("FRIDAY"));  
        System.out.println("Size is now: " + week.size());