Java LinkedHashMap Implementation Explained

LinkedHashMap is a subclass of HashMap that maintains the insertion order or access order through a doubly linked list. It builds upon HashMap by adding a doubly linked list that maintains the order of elements based on their insertion order or access order.

The elements of a LinkedHashMap are stored using the array structure of a HashMap, with each element having a pointer to the previous and next elements, maintaining the order of elements through this double-linked list.

When creating a new LinkedHashMap, you can specify the order of elements as insertion order or access order. If accessOrder is true, the order of elements will be maintained according to access order, meaning the most recently accessed element will be moved to the end of the linked list. If accessOrder is false, the order of elements will be maintained according to insertion order.

By maintaining a doubly linked list, LinkedHashMap ensures the order of elements and allows for elements to be output in a specified order during traversal. This design of LinkedHashMap makes it very efficient for sequential element access, while still retaining the fast lookup and insertion features of HashMap.