In today's insightful lesson, we will delve into a cornerstone of Java's Data Structure ecosystem, the HashMap. Building upon our understanding of HashSets from previous lessons, this session introduces you to HashMaps, a powerful structure that stores key-value pairs. This setup makes HashMap an ideal choice for swift data access through keys is necessary.
HashMaps utilize the principle of hashing, which enables constant time complexity for several core operations, thereby enhancing its efficiency. By the end of this lesson, you will have gained practical knowledge of creating, manipulating, and understanding the workings of HashMaps, including their implementation and complexity in handling data.
Before we commence, let's formally define a HashMap. A HashMap in the world of Java, functions based on a hashtable, implementing the Map interface. This interface implies that HashMaps can store key-value pairs, and interestingly, it allows null values and a null key. HashMaps do not guarantee any specific map order; in other words, the order can change over time.
HashMaps function using the principle of hashing. Here, a key is rendered to a hash code by a hash function, and this numeric code identifies the storage location for the key-value pair. Let's visualize a simple creation of a HashMap:
