Linked HashMap Example

A LinkedHashMap maintains the insertion order. It's slower than the Hashmap for adding and removing elements. It's faster than the HashMap for iterating through the elements of your collection.

Use the LinkedHashMap when the order of insertion is important. For example: showing values in a shopping cart.

LinkedHashMap is an implementation of java.util.Map interface with predictable iteration order (the order of insertion). LinkedHashMap will iterate in the order in which the entries were put into the map.

This implementation differs from HashMap. It maintains a doubly-linked list running through its entries. This linked list defines the iteration ordering. Items are stored in the order in which keys were inserted into the map. The insertion order is not affected if a key is re-inserted into the map.

The other two important implementations of Map interface are java.util.HashMap and java.util.TreeMap. They offer mostly the same functionality. The most important difference is the order in which iteration through the entries will happen. HashMap makes no guarantee about the order. The order can even change completely when new elements are added. TreeMap will iterate according to the “natural ordering” of the keys according to their compareTo() method (or an externally supplied java.util.Comparator). LinkedHashMap will iterate in the order in which the entries were put into the map.