Hash table based implementation of the Map interface. This implementation provides all of the optional map operations, and permits null values and the null key. (The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.)

Mar 7, 2025 · In Java, HashMap is part of the Java Collections Framework and is found in the java.util package. It provides the basic implementation of the Map interface in Java. HashMap stores data in (key, value) pairs. Each key is associated with a value, and you can access the value by using the corresponding key.

All HashMap Methods. A list of all HashMap methods can be found in the table below. Some methods use the type of the HashMap's entries as a parameter or return value. The type of the key will be referred to as K and the type of the value will be referred to as V in the table.

Java HashMap. In the ArrayList chapter, you learned that Arrays store items as an ordered collection, and you have to access them with an index number (int type). A HashMap however, store items in "key/value" pairs, and you can access them by an index of another type (e.g. a String). One object is used as a key (index) to another object (value).

Mar 16, 2023 · HashMap is a data structure that uses a hash function to map identifying values, known as keys, to their associated values. It contains “key-value” pairs and allows retrieving value by key. The most impressive feature is it’s fast lookup of …

Hash table based implementation of the Map interface. This implementation provides all of the optional map operations, and permits null values and the null key. (The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.)

Jan 16, 2025 · In this tutorial, we’ll see how to use HashMap in Java, and we’ll look at how it works internally. A class very similar to HashMap is Hashtable. Please refer to a couple of our other articles to learn more about the java.util.Hashtable class itself and the differences between HashMap and Hashtable. 2. Basic Usage.

In this reference page, you will find all the hashmap methods available in Java. For example, if you need to add an element to the hashmap, use the put () method. remove all elements from HashMap. makes the copy of the hashmap. checks if the HashMap is empty. returns the number of items in HashMap. inserts the specified item to the hashmap.

Dec 5, 2024 · We can create HashMap using different ways, specific to the requirements. For example, we can create an empty HashMap containing no key-value pairs initially. Later, we can add the key-value pairs in this empty HashMap. Additionally, we can specify the initial load capacity and load factor for performance reasons discussed later in this article.

By understanding its methods, use cases, and best practices, you can effectively utilize HashMap in your Java applications. This tutorial covers the essential methods with examples and demonstrates a real-time example with CRUD operations.