What is the difference between ArrayList and LinkedList in Java?

Both ArrayList and LinkedList are commonly used collection classes in Java, with the main difference being their internal data structures and operational efficiency.

1. Internal data structure:

1. ArrayList is a dynamic array implemented based on an array structure, which can dynamically expand its capacity as needed. Consequently, it supports random access, allowing direct access to elements through indexes, but is less efficient when it comes to inserting and deleting elements.
2. LinkedList is implemented based on a doubly linked list, where each element contains references to the previous and next elements. This means that LinkedList supports efficient insertion and deletion operations, but does not support random access and requires traversing the list to find a specific element.

1. Operational efficiency:

1. The efficiency of random access in an ArrayList is higher than that in a LinkedList because elements can be directly accessed through an index with a time complexity of O(1). However, when it comes to insertion and deletion operations, elements need to be shifted, resulting in a time complexity of O(n).
2. The efficiency of insertions and deletions in a LinkedList is higher than in an ArrayList because it only requires changing references of adjacent elements, with a time complexity of O(1). However, accessing elements in a LinkedList requires traversing the entire list, with a time complexity of O(n).

In conclusion, if frequent insertions and deletions are needed, LinkedList can be chosen; if frequent random access operations are needed, ArrayList can be chosen. In actual applications, choose the appropriate collection class based on specific requirements to improve efficiency.