Improve this answer. BalusC 1. I think Set has the same performance with ArrayList?? Set is an interface. HashSet is an implementation that will overall perform better here.
TreeSet will perform between the two, but guarantee order on top of uniqueness. JohnGaughan nitpick clarification: TreeSet guarantees natural order. LinkedHashSet guarantees insertion order. I believe the ArrayList considerations are quite inaccurate, from the documentation: "The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. The add operation runs in amortized constant time, that is, adding n elements requires O n time.
All of the other operations run in linear time roughly speaking. The constant factor is low compared to that for the LinkedList implementation. Show 2 more comments. Makoto Makoto Bonus: Java has LinkedHashSet which iterates in insertion order like lists. Add a comment. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.
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Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 12 years, 1 month ago. Active 6 years, 6 months ago. Viewed 79k times. I currently believe that: When you need a structure from which you will be retrieving items randomly - use a HashMap When you will be retrieving items in order e. Are there situations where this is not correct? Improve this question. Ankur Ankur 48k gold badges silver badges bronze badges. Add a comment. Active Oldest Votes. On a map, you can ask for an element by its key, instead of by its index as you do with a list.
Improve this answer. Using a hashset, you are guaranteed to not have duplicates granted equals and hashcode are implemented correctly. Presumably this is more optimal than testing in List contains a given entry per every insertion operation.
It's also worth noting that if these collections are to be persisted to a database via JPA or an ORM like Hibernate , useful alternative implementations like LinkedHashMap cannot be readily used because of the limited fashion in which ORMs reconstitute collections.
I doubt a linked list would give you better performance. Array access is O 1 , just like a single link traversal, but I'd expect locality of reference to be better with an array, giving you a better results. LinkedList is not significantly better than ArrayList for iterative performance.
And it definitely uses more memory! But it is significantly better for some kinds of list insertion and deletion operations. My comments were a response to, "for pure iterative performance How about addition time over long period? How can you compare ArrayList with HashMap both are different kinds of data structure , Map holds two objects e. Anonymous, that's the difference and aticle says diference between ArrayList and HashMap.
To add on that there are couple of others, which are worth noting : 1 HashMap has load factor to decide when to resized but ArrayList doesn't have load factor.
Hello Prachi, if you just want to store an object than use ArrayList, if you have a mapping e. Feel free to comment, ask questions if you have any doubt. Pages Home core java spring online courses thread java 8 coding sql books oop interview certification free resources best. Difference between ArrayList and HashMap in Java One of the most critical differences between the HashMap and ArrayList class is that the former is the implementation of the hash table while the latter is a dynamic array that can resize itself.
Though both are used to store objects they are completely different in their implementation, working, and usage.
The main difference between ArrayList and HashMap is that ArrayList is an index-based data structure backed by an array while HashMap is a map data structure that works on hashing to retrieve stored values.
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