What is HashMap and Map

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Map is Interface which is part of Java collections framework. This is to store Key Value pair, and Hashmap is class that implements that using hashing technique.

In Core Java:

  1. Map:
    • A Map is an interface in Java that represents a collection of key-value pairs, where each key is associated with exactly one value.
    • It is part of the Java Collections Framework and is designed to store, retrieve, and manipulate data in the form of key-value pairs.
    • Some common implementations of the Map interface include HashMap, TreeMap, and LinkedHashMap.
  2. HashMap:
    • HashMap is a class in Java that implements the Map interface.
    • It is a data structure that allows you to store and retrieve key-value pairs.
    • It is based on the hashing principle, where each key is hashed, and the resulting hash code is used to determine the index at which the corresponding value is stored.
    • HashMap does not guarantee the order of the elements, and it allows null keys and values (with some restrictions).

In summary, a Map is a more general concept representing a collection of key-value pairs, and HashMap is a specific implementation of the Map interface in Java using a hashing mechanism for efficient data retrieval. Other implementations of the Map interface might use different underlying data structures and provide different guarantees regarding order and null values.