Enum map
- 2. Contents ➢ What is EnumMap? ➢ Example ➢ Order of keys ➢ Concurrent Modification Exception ➢ Null Pointer Exception ➢ Synchronization ➢ Why Use EnumMap?
- 3. What is EnumMap? A specialized Map implementation for use with enum type keys. All of the keys in an enum map must come from a single enum type that is specified when the map is created. Enum maps are represented internally as arrays. This representation is extremely compact and efficient. This class is a member of the Java Collections Framework Enum Maps is the part of java Since jdk1.5.
- 4. Example public enum WeekDaysEnum { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY; } EnumMap<WeekDaysEnum,String> enumMap = new EnumMap<>(WeekDaysEnum.class); enumMap.put(WeekDaysEnum.SUNDAY, "SUNDAY"); enumMap.put(WeekDaysEnum.MONDAY, "MONDAY"); for(Entry<WeekDaysEnum, String> week:enumMap.entrySet()){ System.out.println(week.getKey() + " : " + week.getValue()); }
- 5. Order of keys Enum maps are maintained in the natural order of their keys (the order in which the enum constants are declared) . Means iteration will always fetch results according to enum constant order.
- 6. Concurrent Modification Exception Iterators returned by the EnumMap will never throw ConcurrentModificationException. Iterator may or may not show the effects of any modifications to the map that occur while the iteration is in progress. for (Entry<WeekDaysEnum, String> week : enumMap.entrySet()) { System.out.println(week.getKey().name() + " : " + week.getValue()); enumMap.put(WeekDaysEnum.WEDNESDAY, "WEDNESDAY"); }
- 7. Null Pointer Exception Null keys are not permitted. Attempts to insert a null key will throw NullPointerException. EnumMap<WeekDaysEnum, String> enumMap = new EnumMap<>(WeekDaysEnum.class); enumMap.put(null, "FRIDAY");
- 8. Synchronization EnumMap is not synchronized. If multiple threads access an enum map concurrently, and modifying it then it should be synchronized. Map<EnumKey, V> m = Collections.synchronizedMap(new EnumMap<EnumKey, V>(...));
- 9. Why Use EnumMap All basic operations execute in constant time. They are likely (though not guaranteed) to be faster than their HashMap. EnumMap Internally uses array in place of hashing technique.
- 10. Thanks