
Map is an Interface which comes under Java Collection framework.
Main Characteristic of Map Interface
- It is an Object that used to map keys to values.
- A Map cannot contain Duplicate values.
- Every key can map to one value at most.
- This interface is replacement to Dictionary class which was an abstract class instead of Interface.
- Map interface allows 3 collection views
- Set of keys
- Collection of values
- Set of key-value mappings
- As Map provide 3 views as above, It allows you to iterate over keys, values or key value pair.
- Entry can be removed from a Map in a safe way during iteration.
- It is not permissible for a map to contain itself as a key.
- Map can contain itself as value.
- There are some restriction on the keys and values some map implementation can contain.
- Attempting to insert an ineligible key or value throws an unchecked exception.
Concrete Map Implementation
- HashMap
- Hashtable
- EnumMap
- IdentityHashMap
- LinkedHashMap
- Properties
- TreeMap
- WeakHashMap
- ConcurrentSkipListMap
- ConcurrentHashMap
Important Methods in Map Interface
- put(K key, V value) : Put the specified value in map with specified key.
- putAll(Map<? extends K, ? extends V> m) : Copies all mapping from given Map to this Map.
- keySet() : Returns a Set containing the key in this Map.
- values() : Returns a Collection containing all values in this Map.
- isEmpty() : Check if there is any element in given Map or not.
- remove(Object key) : Removes the mapping for a key from this map if it is present.
- containsKey(Object key) : Checks if there any mapping for specified key.
- containsValue(Object value) : Checks if there any mapping for specified Object (Could be more than one).
- get(Object key) : Returns the value to which this key is associated to.
- clear() : Used to remove all the mapping in given Map.
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