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ArrayList vs LinkedList

ArrayList and LinkedList are two of the most commonly used data structures in Java, and understanding the differences between them can help you choose the right data structure for your particular use case.

ArrayList and LinkedList are both part of the Java Collections Framework, which provides a set of interfaces and classes for storing and manipulating groups of objects.

ArrayList is implemented as a resizable array, while LinkedList is implemented as a doubly linked list. The most important difference between these two data structures is their underlying implementation, which can affect performance and memory usage.

Here are some of the key differences between ArrayList and LinkedList:

Insertion and deletion performance:​

ArrayList provides constant-time O(1) access to elements based on their index, which means that accessing an element in the list takes the same amount of time, regardless of the size of the list. However, inserting or deleting an element in the middle of an ArrayList requires shifting all subsequent elements to the right or left, which can be a costly operation. The worst-case scenario for insertion or deletion in an ArrayList is O(n), where n is the number of elements in the list.

LinkedList, on the other hand, provides O(1) insertion and deletion performance, since each element in the list has a pointer to the next and previous elements. However, accessing an element at a particular index in a LinkedList requires iterating over all the elements in the list until you reach the desired index, which can be a costly operation. The worst-case scenario for accessing an element in a LinkedList is also O(n), where n is the number of elements in the list.

Memory usage​

ArrayList uses a contiguous block of memory to store elements, which means that it requires a fixed amount of memory, regardless of the number of elements in the list. This makes ArrayList a more memory-efficient data structure for small to medium-sized lists.

LinkedList, on the other hand, uses pointers to link elements together, which means that it requires more memory overhead than ArrayList. Each element in a LinkedList requires two pointers (one to the next element and one to the previous element), which can add up to a significant amount of memory usage for large lists.

Iteration performance:​

Iterating over all the elements in an ArrayList is generally faster than iterating over all the elements in a LinkedList. This is because ArrayList provides O(1) access to elements based on their index, while LinkedList requires iterating over all the elements in the list until you reach the end.

When to use ArrayList:​

  • When you need to access elements in the list based on their index.
  • When you need to iterate over all the elements in the list frequently.
  • When you have a small to medium-sized list and memory usage is a concern.

When to use LinkedList:​

  • When you need to insert or delete elements frequently.
  • When you have a large list and memory usage is not a concern.
  • When you need to maintain the order of the elements in the list.