![]() ![]() Let's suppose a HashMap is created with the initial default capacity of 16 and the default load factor of 0.75. Collision: A collision occurs when a hash function returns the same bucket location for two different keys.When the number of entries in the hash table exceeds the threshold value, the Map is rehashed so that it has approximately twice the number of buckets as before. Rehashing: Rehashing is the process of re-calculating the hash code of already stored entries.Threshold: The threshold of a HashMap in Java is approximately the product of the current capacity and load factor.The default load factor is 75% of the capacity. The load factor is the measure that decides when to increase the capacity of the Map. ![]() Load Factor: The capacity is expanded as the number of elements in the HashMap increases.The initial default capacity of the HashMap is 16`. The initial capacity is the capacity at which the Map is created. Capacity: Capacity is the number of buckets in the HashMap.This helps it quickly find all Node(s) with the same specified hashcode. HashMap ensures those Node(s) having the same hashcode will have consecutive references. It may not be the next element in the array. The next field is a reference to the next Node object. HashMap manages an array of Node objects that will be replaced by another larger array if all of its elements has been assigned value. So the Hash function is applied to the key object to calculate the index of the bucket in order to store and retrieve any key-value pair. hashCode() method of object class returns the memory reference of object in integer form. Hashing is a process of converting an object into integer form by using the method hashCode(). Hashing: HashMap in Java works on the principle of hashing - an algorithm to map object data to some representative integer values.HashMap(int initialCapacity, float loadFactor)īefore discussing the constructors in detail, let's take a deep dive into a few other terms for better understanding:.HashMap in Java has 4 constructors, and each one has public access modifier. The HashMap in Java implements Serializable, Cloneable, Map interfaces. ![]() We will learn more about the put() method later in this article. Here, we have used the put() method to add elements to the hashmap. In the above example, we have created a HashMap named languages. After the import is done, we can create HashMap in Java as below: Example: Create HashMap in Javaįirst, the package needs to be imported to create a HashMap in Java. We will look at the performance of HashMap in Java later in the article. The advantage of HashMap is that the time complexity to insert and retrieve a value is O ( 1 ) O(1) O ( 1 ) on average, and space complexity is O ( n ) O(n) O ( n ). To find a specific element in a list, the time complexity is O ( n ) O(n) O ( n ) for insertion and lookup and if the list is sorted, it will be O ( l o g n ) O(log n) O ( l o g n ) on using binary search. Now, one might question that if we simply want to add values, then why can't we use a list? Why do we need HashMap? The simple reason is performance. HashMap in Java is the implementation of map, which is a key-value mapping.
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