Hashmap which maintains order

Consider making your items sortable. In the case of strings, there is already a natural ordering; alphabetical. You can make objects that use the sortable class, and therefore you can use sorting algorithms to put these objects in a nice order, no matter what order you get them in from hash! It's time for a LinkedHashMap , it is meant exactly to preserve insertion order. Mind that even a TreeMap exists, which allows you to keep your desired order by using Comparable interface.

It is not an hash map anymore, but a tree. If you truly are unable to switch to another Map implementation LinkedHashMap is exactly what you want , then the only other possibility is to retain the original List, and use it to create the new List from the Map. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Maintaining order in HashMap [duplicate] Ask Question.

Asked 8 years, 1 month ago. Active 8 years, 1 month ago. Viewed 42k times. Improve this question. Add a comment. Active Oldest Votes. HashMap : This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time. And LinkedHashMap : Hash table and linked list implementation of the Map interface, with predictable iteration order. Improve this answer. Jon Skeet Jon Skeet 1.

Sir, I cannot change the implementation of the map because it is being used at a lot of other places! Save Close. Dashboard Logout. LinkedHashMap int capacity, float fillRatio This constructor initializes both the capacity and the fill ratio. LinkedHashMap int capacity, float fillRatio, boolean Order This constructor allows you to specify whether the elements will be stored in the linked list by insertion order, or by order of last access.

Object get Object key Returns the value to which this map maps the specified key. Entry eldest Returns true if this map should remove its eldest entry. A Map 's keys can be any value including functions, objects, or any primitive.

The keys of an Object must be either a String or a Symbol. The keys in Map are ordered. Thus, when iterating over it, a Map object returns keys in order of insertion. What is LinkedHashMap?

LinkedHashMap is a Hash table and linked list implementation of the Map interface, with predictable iteration order. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map insertion-order. How do you sort an ArrayList? To sort the ArrayList, you need to simply call the Collections.

This method will sort the elements country names of the ArrayList using natural ordering alphabetically in ascending order. Lets's write some code for it. Will ArrayList maintain insertion order? ArrayList maintains the insertion order i. HashSet is an unordered collection and doesn't maintain any order.

ArrayList allows duplicate values in its collection. Which is faster ArrayList or linked list? ArrayList is faster than LinkedList if I randomly access its elements. ArrayList has direct references to every element in the list, so it can get the n-th element in constant time.

LinkedList has to traverse the list from the beginning to get to the n-th element. LinkedList is faster than ArrayList for deletion. Why insertion is faster in linked list? If any element is removed from the array, all the bits are shifted in memory. Manipulation with LinkedList is faster than ArrayList because it uses doubly linked list so no bit shifting is required in memory.