What is the Difference Between Map and Hashmap

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Map is Interface and Hashmap is class that implements that

In Java, Map is an interface that represents a collection of key-value pairs, where each key is associated with exactly one value. HashMap is a specific implementation of the Map interface.

Here are some key differences between Map and HashMap:

  1. Interface vs. Implementation:
    • Map is the interface that defines the basic contract for implementing a map data structure.
    • HashMap is a class that implements the Map interface and provides a specific way to store and retrieve key-value pairs.
  2. Synchronization:
    • Map is not synchronized, meaning it is not thread-safe. Multiple threads can access it concurrently without any restriction.
    • HashMap is also not synchronized. If you need a synchronized version, you can use Collections.synchronizedMap(Map) to obtain a synchronized map.
  3. Null Keys and Values:
    • Map allows a single null key and multiple null values.
    • HashMap allows a single null key and multiple null values. In fact, it allows one null key and any number of null values.
  4. Ordering:
    • The Map interface does not guarantee any specific order of elements.
    • HashMap does not guarantee any specific order of elements. If you need ordering, you can use LinkedHashMap, which maintains the order of the elements based on their insertion order.
  5. Performance:
    • HashMap generally has better performance compared to some other map implementations for most operations (such as adding, removing, and retrieving elements). However, performance characteristics may vary depending on the specific use case.
  6. Iterating:
    • When you iterate over a Map, the order of the elements is not guaranteed.
    • If you need predictable iteration order, you can use a LinkedHashMap.

In summary, Map is an interface, and HashMap is a specific implementation of that interface with certain characteristics. Depending on your requirements, you may choose different implementations of the Map interface, such as HashMap, TreeMap, or LinkedHashMap.