Mary –> France Storing Custom objects as KeyĪs you can see, we are getting correct output after using Collections.synchronizedMap() and making incrementTime synchronized. Iterating over HashMap’s entrySet with foreach loop Iterating over HashMap’s entrySet with foreach and lambda Iterating over HashMap’s entrySet with iterator Iterating over HashMap’s keyset() with foreach and lambda: Iterating over HashMap using keyset() with foreach loop: Iterating over HashMap with foreach and lambda: Public HashMap(Map m): This constructor is used when you want to create HashMap from some other Map such as TreeMap or LinkedHashMap. In most of the scenarios, you should avoid using this constructor unless you are sure about this as load factor 0.75 provides a good tradeoff between time and space. Public HashMap(int initialCapacity,float loadFactor): This constructor is used to specify initial capacity of the HashMap and load factor. Public HashMap(int initialCapacity): This constructor is used to specify the initial capacity of HashMap and default load factor 0.75. It creates an empty HashMap with default initial capacity of 16 and load factor 0.75. Public HashMap(): This is the default constructor and used mostly. Yes, Just to make things more obvious, HashMap implements Map interface again and there is nothing wrong in implementing interface again.You don’t have to go through class Hierarchy to find it out that HashMap implements Map interface. (m.getKey()+" "+m.Did you notice HashMap implements Map interface even if AbstractMap already implements it? ("After invoking the putIfAbsent() method:: ") * This class is used to show the HashMap functionality. It will return the number of entries on the map. It will return a collection view of the values contained in the map. It will replace 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. It will replace the old value with the new value for a specified key. It will replace the specified value for a specified key.īoolean replace(K key, V oldValue, V newValue) It will associate the specified key with the given non-null value if it is not already associated with a value or is associated with null. V merge(K key, V value, BiFunction remappingFunction) It will return true if the map is empty returns false if it contains at least one key. It will return 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) It will return the object that contains the value associated with the key. It will perform the given action for each entry in the map until all entries have been processed or the action throws an exception. It will compare the specified Object with the Map. It will return true if some key equal to the key exists within the map, else return false. It will return true if some value equal to the value exists within the map, else return false. 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 will 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 will 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 will eliminate or delete the specified values with the associated specified keys from the map. It will delete or eliminate an entry for the specified key. It will add the specified value with the specified key in the map only if it is not already specified. It will add the specified map to the map. It will return a set view of the keys contained in this map. It will return a collection view of the mappings contained in this map. It will return a shallow copy of this HashMap instance: the keys and values themselves are not cloned. It will return true if this map contains no key-value mappings. It will eliminate or delete all of the mappings from this map. It will create and initialize both the capacity and load factor of the hash map by using its arguments. It will create and initialize the capacity of the hash map to the given integer value, capacity. It will create and initialize the hash map by using the elements of the given Map object m. K: The type of keys maintained by the HashMap.Public class HashMap extends AbstractMap implements Map, Cloneable, Serializable No order is maintained by the HashMap class.
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