It replaces the old value with the new value for a specified key. It replaces the specified value for a specified key.Д«oolean replace(K key, V oldValue, V newValue) If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.

V merge(K key, V value, BiFunction remappingFunction) This method returns true if the map is empty returns false if it contains at least one key. It returns the value to which the specified key is mapped, or defaultValue if the map contains no mapping for the key. V getOrDefault(Object key, V defaultValue)

This method returns the object that contains the value associated with the key. It performs the given action for each entry in the map until all entries have been processed or the action throws an exception. It is used to compare the specified Object with the Map. This method returns true if some key equal to the key exists within the map, else return false. This method returns true if some value equal to the value exists within the map, else return false. 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. V computeIfPresent(K key, BiFunction remappingFunction) 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. V computeIfAbsent(K key, Function mappingFunction) It is used to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping). V compute(K key, BiFunction remappingFunction) It removes the specified values with the associated specified keys from the map. It is used to delete an entry for the specified key. It inserts the specified value with the specified key in the map only if it is not already specified. It is used to insert the specified map in the map. It is used to insert an entry in the map. It is used to return a set view of the keys contained in this map. It is used to return a collection view of the mappings contained in this map. It is used to return a shallow copy of this HashMap instance: the keys and values themselves are not cloned. It is used to return true if this map contains no key-value mappings. It is used to remove all of the mappings from this map. It is used to initialize both the capacity and load factor of the hash map by using its arguments. It is used to initializes the capacity of the hash map to the given integer value, capacity. It is used to initialize the hash map by using the elements of the given Map object m. It is used to construct a default HashMap. K: It is the type of keys maintained by this map.Д¬onstructors of Java HashMap class Constructor.Public class HashMap extends AbstractMap implements Map, Cloneable, Serializable The initial default capacity of Java HashMap class is 16 with a load factor of 0.75.ДЄs shown in the above figure, HashMap class extends AbstractMap class and implements Map interface.

Java HashMap may have one null key and multiple null values.

Java HashMap contains only unique keys.

Java HashMap contains values based on the key.

It inherits the AbstractMap class and implements the Map interface. Since Java 5, it is denoted as HashMap, where K stands for key and V for value. It allows us to store the null elements as well, but there should be only one null key. HashMap in Java is like the legacy Hashtable class, but it is not synchronized.

HashMap class is found in the java.util package. It is easy to perform operations using the key index like updation, deletion, etc. If you try to insert the duplicate key, it will replace the element of the corresponding key. Java HashMap class implements the Map interface which allows us to store key and value pair, where keys should be unique.

Hashmap java