Internal working of Hashmap:
HashMap is a data structure in Java that is used to store and retrieve key-value pairs. It uses a hash table for storage and retrieval, where each key is hashed and the resulting hash code is used to index the corresponding value.
Internal Working of Hashmap?
Here is the basic internal working of
HashMap in Java:
- When a new
HashMapobject is created, it is initialized with a default capacity and load factor.
- The key-value pairs are stored in an array called the table. Initially, the table is empty.
- When a key-value pair is added to the
HashMap, the key is hashed to generate an index in the table. If the table location is empty, the key-value pair is stored at that location. If the location is not empty, a collision occurs.
- In the case of a collision, the
HashMapuses a linked list to store all the key-value pairs that have the same hash code. Each element of the linked list contains a key-value pair and a reference to the next element in the list.
- When a key-value pair is retrieved from the
HashMap, the key is hashed to determine the index in the table. The
HashMapthen searches the linked list at that index to find the key-value pair with the matching key.
- If the
HashMapneeds to be resized due to an increase in the number of key-value pairs, a new, larger table is created, and all the key-value pairs are rehashed and stored in the new table.
HashMap provides constant-time performance for basic operations such as adding, retrieving, and removing key-value pairs, as long as the load factor is maintained at a reasonable level. However, if the load factor becomes too high, collisions will occur more frequently, which can slow down the performance of the
HashMap. To maintain good performance, it is important to choose an appropriate initial capacity and load factor for the
HashMap. Internal Working of Hashmap?
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Hashmap vs HashtTable vs Hashset
HashMap, HashTable, and HashSet are all data structures in Java that are used to store and manipulate collections of data.
HashMap and HashTable are both implementations of the Map interface and use key-value pairs to store and retrieve data. The main difference between them is that HashMap is not synchronized, meaning that it is not thread-safe and can lead to inconsistent behavior when accessed by multiple threads simultaneously, whereas HashTable is synchronized and therefore thread-safe. Internal Working of Hashmap?
HashSet, on the other hand, is an implementation of the Set interface and stores a collection of unique elements, meaning that it does not allow duplicates. HashSet uses a hash table to store and retrieve its elements, similar to HashMap and HashTable.
In terms of performance, HashMap and HashSet both provide constant-time O(1) performance for most operations, including insertion, deletion, and retrieval. However, HashTable’s synchronized nature can make it slower in multi-threaded environments. Internal Working of Hashmap?
In summary, HashMap and HashTable are used for key-value pair mappings, with HashTable providing thread-safety at the expense of performance, while HashSet is used for unique element storage.
Collection important interview Questions
Here are some important interview questions related to Java Collections: Internal Working of Hashmap?
- What is the difference between List and Set in Java Collections?
- What is the difference between ArrayList and LinkedList in Java Collections?
- What is the difference between HashMap and HashTable in Java Collections?
- What is the difference between TreeMap and TreeSet in Java Collections?
- What is the difference between Iterator and ListIterator in Java Collections?
- What is the difference between Collection and Collections in Java?
- What is the difference between Comparable and Comparator interfaces in Java Collections?
- What is the difference between fail-fast and fail-safe iterators in Java Collections?
- How do you sort an ArrayList in descending order in Java Collections?
- What is the use of the toArray() method in Java Collections?
These are just a few examples of questions related to Java Collections that you may encounter in an interview. It is important to have a good understanding of the different types of collections and their uses, as well as their common methods and interfaces. Additionally, it is always helpful to have some practical experience working with collections in Java.
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