In Java, the Map interface is a collection that maps keys to values. Each key can map to at most one value, and the keys in a Map must be unique. The Map interface is part of the java.util package and is implemented by several classes, including HashMap, TreeMap, and LinkedHashMap.

Here are some of the most commonly used methods in the Map interface:

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

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

3. boolean containsValue(Object value): This method returns true if the Map 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 Map.

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 Map contains no key-value mappings, otherwise false.

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

8. V put(K key, V value): This method associates the specified value with the specified key in the Map. If the Map 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 Map.

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

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

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

These methods provide the basic functionality to manipulate a Map. The choice of which method to use depends on the specific requirements of the application.