University of Central Florida (UCF) COP3330 Object Oriented Programming Final Practice Exam

A HashMap in Java is an implementation of the Map interface that uses a hash table for storage. This means that it allows for the efficient retrieval and storage of key-value pairs. The keys in a HashMap are hashed, and the resulting hash code determines the index at which the entry is stored within the table. This design enables average constant-time complexity for basic operations such as getting, putting, and removing elements.

Additionally, a HashMap does not maintain the order of its elements, contrasting it with data structures like TreeMap, which sorts entries based on the natural ordering of the keys or a specified comparator. Each key in a HashMap is unique, meaning that if you attempt to insert a key that already exists in the map, the new value will replace the existing value for that key.

Thus, the ability of a HashMap to store key-value pairs efficiently with unique keys is a fundamental characteristic of this data structure, making it ideal for various applications where quick access to data is necessary.