Arraylist or hashmap which is better

The third difference between HashMap and ArrayList is that keys of HashMap must implement equals and hashCode method correctly, ArrayList doesn't have that requirement but its good to have that because contains method of ArrayList will use the equals method to see if that object already exists or not. The fourth difference between HashMap and ArrayList is that ArrayList maintains the order of objects, in which they are inserted while HashMap doesn't provide any ordering guarantee.

Another difference between ArrayList and HashMap is that ArrayList allows duplicates but HashMap doesn't allow duplicates key though it allows duplicate values. ArrayList get index method always gives an O 1 performance but HashMap get key can be O 1 in the best case and O n in the worst case. They both are completely different from each other and exist for different purposes.

Use HashMap if you need a map kind of structure to map keys to values and use ArrayList if you just looking to store objects in Java. Labels: ArrayList , core java , Java collection tutorial. Ethical Hacking. Computer Graphics. Software Engineering. Web Technology. Cyber Security. C Programming. Control System. Data Mining. Data Warehouse. Javatpoint Services JavaTpoint offers too many high quality services.

ArrayList vs. For each value, there must be a key associated with HashMap. Syntax: ArrayList list. Skip to content. Change Language. Related Articles. Table of Contents. Save Article.

Improve Article. Like Article. Last Updated : 09 Nov, Asked 8 years, 1 month ago. Active 8 years, 1 month ago. Viewed 59k times. Using ArrayList or HashMap 1. Konstantin Burov Why dont you test it? I want to know if have any better pattern for my problem — hieuxit. If you only want to insert items that aren't already in the collection, why not use a Set?

Often, certain programmers spend too much time addressing performance problems that don't yet exist. If your application spends only a fraction of its time accessing your data in this way then, frankly, the implementation of HashMap or ArrayList may not even matter one iota. The only way anybody can say that this detail is important for performance is by profiling your application. Trying to first find and then fix a reason for a big application being slow is often a big task.

Show 1 more comment. Active Oldest Votes. So finally, to answer your question, my advice is to use the HashMap. BalusC 1. I think Set has the same performance with ArrayList?? Set is an interface.