Question: What are the Useful methods of Map interface?

Answer: Method:   V put(Object key, Object value)
Description: It is used to insert an entry in the map.

Method:   void putAll(Map map)
Description: It is used to insert the specified map in the map.

Method:   V putIfAbsent(K key, V value)
Description: It inserts the specified value with the specified key in the map only if it is not already specified.

Method:   V remove(Object key)
Description: It is used to delete an entry for the specified key.

Method:  boolean remove(Object key, Object value) 
Description: It removes the specified values with the associated specified keys from the map.

Method:   Set keySet()
Description: It returns the Set view containing all the keys

Method: Set<Map.Entry<K,V>> entrySet()  
Description: It returns the Set view containing all the keys and values.

Method:   void clear()
Description: It is used to reset the map.

Method:   V compute(K key, BiFunction<? super K,? super V,? extends V> remappingFunction)
Description: It is used to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping).


Method:  V computeIfAbsent(K key, Function<? super K,? extends V> mappingFunction) 
Description: It is used to compute its value using the given mapping function, if the specified key is not already associated with a value (or is mapped to null), and enters it into this map unless null.

Method:   V computeIfPresent(K key, BiFunction<? super K,? super V,? extends V> remappingFunction)
Description: It is used to compute a new mapping given the key and its current mapped value if the value for the specified key is present and non-null.

Method:   boolean containsValue(Object value)
Description: This method returns true if some value equal to the value exists within the map, else return false.

Method:   boolean containsKey(Object key)
Description: This method returns true if some key equal to the key exists within the map, else return false.

Method:  boolean equals(Object o) 
Description: It is used to compare the specified Object with the Map.

Method:   void forEach(BiConsumer<? super K,? super V> action)
Description: It performs the given action for each entry in the map until all entries have been processed or the action throws an exception.

Method:   V get(Object key)
Description: This method returns the object that contains the value associated with the key.

Method:  V getOrDefault(Object key, V defaultValue) 
Description: It returns the value to which the specified key is mapped, or defaultValue if the map contains no mapping for the key.

Method:   int hashCode()
Description: It returns the hash code value for the Map

Method: boolean isEmpty()  
Description: This method returns true if the map is empty; returns false if it contains at least one key.

Method:   V merge(K key, V value, BiFunction<? super V,? super V,? extends V> remappingFunction)
Description: If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.

Method:   V replace(K key, V value)
Description: It replaces the specified value for a specified key.

Method:   boolean replace(K key, V oldValue, V newValue)
Description: It replaces the old value with the new value for a specified key.

Method:   void replaceAll(BiFunction<? super K,? super V,? extends V> function)
Description: It replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception.

Method:   Collection values()
Description: It returns a collection view of the values contained in the map.

Method:   int size()
Description: This method returns the number of entries in the map.