In this tutorial, we will learn about the Java Map interface and its methods.
A map contains values on the basis of key, i.e. key and value pair. Each key and value pair is known as an entry. A Map contains unique keys.
A Map is useful if you have to search, update or delete elements on the basis of a key.
Working of Map
In Java, elements of Map are stored in key/value pairs. Keys are unique values associated with individual Values. A map cannot contain duplicate keys. And, each key is associated with a single value.
| Sr.No. | Method & Description |
|---|---|
| 1 | void clear( ) Removes all key/value pairs from the invoking map. |
| 2 | boolean containsKey(Object k) Returns true if the invoking map contains k as a key. Otherwise, returns false. |
| 3 | boolean containsValue(Object v) Returns true if the map contains v as a value. Otherwise, returns false. |
| 4 | Set entrySet( ) Returns a Set that contains the entries in the map. The set contains objects of type Map.Entry. This method provides a set-view of the invoking map. |
| 5 | boolean equals(Object obj) Returns true if obj is a Map and contains the same entries. Otherwise, returns false. |
| 6 | Object get(Object k) Returns the value associated with the key k. |
| 7 | int hashCode( ) Returns the hash code for the invoking map. |
| 8 | boolean isEmpty( ) Returns true if the invoking map is empty. Otherwise, returns false. |
| 9 | Set keySet( ) Returns a Set that contains the keys in the invoking map. This method provides a set-view of the keys in the invoking map. |
| 10 | Object put(Object k, Object v) Puts an entry in the invoking map, overwriting any previous value associated with the key. The key and value are k and v, respectively. Returns null if the key did not already exist. Otherwise, the previous value linked to the key is returned. |
| 11 | void putAll(Map m) Puts all the entries from m into this map. |
| 12 | Object remove(Object k) Removes the entry whose key equals k. |
| 13 | int size( ) Returns the number of key/value pairs in the map. |
| 14 | Collection values( ) Returns a collection containing the values in the map. This method provides a collection-view of the values in the map. |