What is difference between Array List And LinkedList ?

 ArrayList and LinkedList are two different types of data structures in Java that are used to store and manipulate collections of objects. The main difference between them lies in the way they store and access elements.

1. Memory allocation: An ArrayList internally uses an array to store the elements, while a LinkedList uses a doubly linked list.

2. Random Access: ArrayList provides constant-time access to elements based on their index, i.e., O(1) time complexity, whereas LinkedList requires O(n) time complexity to access elements based on their index.

3. Insertion and deletion: Inserting or deleting elements from an ArrayList requires shifting elements to maintain the order, which can be an expensive operation for large arrays. In contrast, insertion or deletion operations in a LinkedList are faster because they only require updating a few pointers.

4. Memory usage: ArrayList requires more memory compared to LinkedList because it needs to allocate memory for the entire array. In contrast, LinkedList only needs to allocate memory for each individual node in the list.

5. Iteration: ArrayList is faster than LinkedList for sequential access, i.e., iterating through all elements, because it provides constant-time access to elements. In contrast, LinkedList requires O(n) time complexity to traverse all elements.

In general, ArrayList is a better choice when the focus is on random access, and the list is not frequently modified. On the other hand, LinkedList is a better choice when the focus is on frequent modification of the list, such as insertion or deletion, and sequential access is more common.