HashMap In Java In Java, HashMap is a widely used data structure that belongs to the Java Collections Framework. It is part of the java.util package and implements the Map interface. HashMap stores key-value pairs, where each key is associated with a corresponding value. Here are some key points about HashMap in Java: Key-Value Pairs: Each element in a HashMap is a key-value pair. Keys must be unique, but values can be duplicated. Null Keys and Values: A HashMap can have one null key. It can have multiple null values. Ordering: HashMap does not guarantee any specific order of elements. If you need ordering, you can use LinkedHashMap, which maintains the order of insertion. Performance: The performance of HashMap is generally O(1) for basic operations (get, put, remove), assuming a good hash function and proper handling of collisions. The actual performance may degrade in the presence of collisions (when different keys hash to the same bucket). Synchronization: HashMap is not synchronized, meaning it is not thread-safe. For thread-safe operations, you can use Collections.synchronizedMap(Map) to create a synchronized version or use ConcurrentHashMap which provides better concurrent performance. Click on link for more knowledge - https://www.youtube.com/watch?v=E0-c7H5VNp0