DSA Complete Course in Java #3 HashMap in Java

DSA Complete Course in Java #3 HashMap in Java
HashMap(K, V) is a part of Java’s collection since Java 1.2. This class is found in java.util package. It provides the basic implementation of the Map interface of Java. It stores the data in (Key, Value) pairs, and you can access them by an index of another type (e.g. an Integer). One object is used as a key (index) to another object (value). If you try to insert the duplicate key, it will replace the element of the corresponding key.

HashMap is similar to HashTable, but it is unsynchronized. It allows to store the null keys as well, but there should be only one null key object and there can be any number of null values. This class makes no guarantees as to the order of the map. To use this class and its methods, you need to import java.util.HashMap package or its superclass.

Parameters: It takes two parameters namely as follows:

The type of keys maintained by this map
The type of mapped values
HashMap implements Serializable, Cloneable, Map(K, V) interfaces. HashMap extends AbstractMap(K, V) class. The direct subclasses are LinkedHashMap, PrinterStateReasons.

Constructors in HashMap is as follows:
HashMap provides 4 constructors and the access modifier of each is public which are listed as follows:

HashMap()
HashMap(int initialCapacity)
HashMap(int initialCapacity, float loadFactor)
HashMap(Map map)

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