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.Ĭonstructors 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.Īs 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. Map immutableMap = Map.Java HashMap class implements the Map interface which allows us to store key and value pair, where keys should be unique. boolean isEmpty() checks if a map contains no key-value mappings, O(1).int size() gets the number of key-value mappings in a map, O(1).boolean containsValue(Object value) method checks if a map contains a mapping for the specified value.boolean containsKey(Object key) method checks if a map contains a mapping for the specified key.Java 8+ V getOrDefault(Object key, V defaultValue) method gets the value mapped to the key argument or defaultValue if there is no mappings for the key.The returned value may be null if the key is mapped to null or there is no mapping value to it V get(Object key) method gets the value mapped to the key argument ImmutableMap.values().forEach(System.out::println) Collection values() method gets all values contained in the map.ImmutableMap.keySet().forEach(System.out::println) Set keySet() method gets all keys contained in the map.ImmutableMap.entrySet().forEach(System.out::println) Set> entrySet() method gets all key-value mappings entries contained in the map.You can query a HashMap in Java with entrySet(), keySet() and values() methods to get all keys and values mapping get methods to return value by the specified key containsKey and containsValue methods to check existing size and isEmpty methods to check the HashMap size Get all HashMap keys and values
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