In Java, EnumMap is a class that implements the Map interface and is designed to be used with enum types as keys. It is part of the java.util package and provides a highly optimized implementation for mapping enums to values.

EnumMap is similar to other Map implementations, such as HashMap or TreeMap, but it is designed to take advantage of the fact that enums have a fixed number of values and can be efficiently represented as arrays. By using arrays internally, EnumMap can provide better performance and reduced memory overhead compared to other Map implementations.

Here are some of the most commonly used methods in the EnumMap class:

1. void clear(): This method removes all the key-value mappings from the EnumMap.

2. boolean containsKey(Object key): This method returns true if the EnumMap contains a mapping for the specified key, otherwise false.

3. boolean containsValue(Object value): This method returns true if the EnumMap contains one or more mappings to the specified value, otherwise false.

4. Set<Map.Entry<K, V>> entrySet(): This method returns a Set view of the key-value mappings in the EnumMap.

5. V get(Object key): This method returns the value to which the specified key is mapped, or null if the key is not mapped to any value.

6. boolean isEmpty(): This method returns true if the EnumMap contains no key-value mappings, otherwise false.

7. Set<K> keySet(): This method returns a Set view of the keys in the EnumMap.

8. V put(K key, V value): This method associates the specified value with the specified key in the EnumMap. If the EnumMap previously contained a mapping for the key, the old value is replaced with the new value and the old value is returned.

9. void putAll(Map<? extends K, ? extends V> m): This method copies all of the mappings from the specified Map to this EnumMap.

10. V remove(Object key): This method removes the mapping for the specified key from the EnumMap, if it is present.

11. int size(): This method returns the number of key-value mappings in the EnumMap.

12. Collection<V> values(): This method returns a Collection view of the values in the EnumMap.

The keys in an EnumMap must be instances of the same enum type, and the values can be of any type. When an EnumMap is created, it must be initialized with all the possible keys of the enum type, which allows the EnumMap to be implemented as an array internally. This means that EnumMap can provide constant-time performance for most operations, making it a highly efficient choice for mapping enums to values.