Difference between arraylist & linkedlist
ArrayList and LinkedList are both implementations of the List interface in Java, but they have different underlying data structures and performance characteristics:

Table of Contents
1. Underlying Data Structure:
- ArrayList uses a dynamic array to store elements internally. It dynamically resizes its internal array when needed to accommodate more elements.
- LinkedList uses a doubly linked list to store elements internally. Each element is stored as a separate node, and each node maintains references to the previous and next nodes in the list.
2. Performance:
- ArrayList provides faster access to elements by index (random access) because it directly indexes into the underlying array. Retrieving an element by index has a time complexity of O(1).
- LinkedList provides slower access to elements by index because it needs to traverse the list from the beginning or end to reach the desired index. Retrieving an element by index has a time complexity of O(n).
- Insertions and deletions at the end of the list are faster in ArrayList compared to LinkedList because ArrayList does not require traversal to reach the end. Appending an element has a time complexity of O(1) for ArrayList and O(n) for LinkedList (due to traversal to the end).
3. Memory Overhead:
- ArrayList has less memory overhead per element compared to LinkedList because it only needs to store the elements in a contiguous array.
- LinkedList has more memory overhead per element compared to ArrayList because it needs to store additional pointers (references to the previous and next nodes) for each element.
4. Iterating Over Elements:
- ArrayList provides faster iteration over elements using indexed for loops because it supports random access. Iterating over elements has a time complexity of O(n).
- LinkedList provides slower iteration over elements compared to ArrayList because it needs to traverse the list from one node to the next. Iterating over elements also has a time complexity of O(n).
5. Use Cases:
- ArrayList is suitable for scenarios where random access and fast iteration are important, such as when frequent access or modifications are made to elements at specific indices.
- LinkedList is suitable for scenarios where frequent insertions or deletions are made at the beginning or middle of the list, as well as when memory fragmentation is a concern.
In summary, the choice between ArrayList and LinkedList depends on the specific requirements of the application. ArrayList is generally preferred for scenarios requiring random access and fast iteration, while LinkedList is preferred for scenarios requiring frequent insertions or deletions.