Why HashMaps are Better than Arrays

A HashMap in Java is a data structure that is used to store data in the form of key-value pairs. It's part of the Java Collections Framework and is very popular because of its efficiency and simplicity.
Key characteristics of a HashMap include:
HashMap stores data as key-value pairs, meaning you can retrieve a value using its corresponding key.
It does not allow duplicate keys. If you try to insert a duplicate key, the new value will replace the old value associated with that key.
HashMap allows one null key and multiple null values, which means you can have null as a key or a value in the map.
By default, HashMap is not synchronized, which means it is not thread-safe. If you need to use it in a multi-threaded environment, you should either synchronize it manually or use a ConcurrentHashMap.
HashMap does not guarantee any specific order for the stored key-value pairs. The order can change over time as elements are added or removed.
Internally, HashMap works by using a technique called hashing:
When you add a key-value pair to a HashMap, the key is hashed to produce a hash code. This hash code determines where in the internal array the entry will be stored.
HashMap uses an array of nodes called buckets to store its entries. Each bucket is essentially a list that holds all entries that hash to the same index.
If two keys produce the same hash code, a collision occurs. HashMap handles collisions using a linked list. When a collision happens, the new entry is added to the linked list in the corresponding bucket.
HashMap uses a load factor to decide when to resize. By default, the load factor is 0.75, which means that the HashMap will increase its capacity when it is 75% full. This resizing involves creating a larger array and rehashing all existing entries.
Common operations with HashMap include:
Adding elements using the put method, which takes a key and a value. If the key already exists, the associated value is updated.
Accessing elements using the get method, which returns the value associated with a given key. If the key is not found, it returns null.
Removing elements using the remove method, which deletes the entry for a specific key.
Checking for the existence of keys or values using containsKey and containsValue methods.
Iterating through elements by using keySet, values, or entrySet methods to go through the keys, values, or key-value pairs.
HashMap is widely used due to its fast performance for basic operations like adding, removing, and looking up elements. However, because it does not maintain the order of elements and is not synchronized by default, it might not be suitable for all use cases, especially in multi-threaded environments or where the order of elements is important.