Accessing complexity
Actually, if you don't want to entirely read this article, you should know that in almost all cases accessing a list is faster.
When you're accessing a hashmap, you'll first create a hash representation of your key, get to the right "bucket" and then get the value from an implemented list, whereas accessing a value from an ArrayList will merely fetch the value from the list.
After this fact, you might not want to use Maps, but don't worry, there's more..
Two Entirely Different Datastructures
You should never forget that both Map and List are two entirely different datastructures, each with its own advantages.
For example, the keys for a Map aren't linear. Anything can be the key, which becomes very handy when dealing with Strings as keys.
Remember this:
If you need a List, use a list. If you need a Map, use a Map. If at any time you can pick one of both data structures - for example when dealing with consecutive Integers as keys - you're probably better off picking the ArrayList implementation.
But there's more
Remember ArrayList isn't the only List implementation! Choosing the right interface is a first step to choosing the right datastructure, but sometimes a lot of performance can be gained by using another implementation of the chosen interface.If you frequently add elements to the beginning of a List or iterate over the List to delete elements from its interior, you should consider using LinkedList.
Lists: ArrayLists, LinkedList, Vector (synchronised list)
Maps: HashMap, TreeMap, LinkedHashMap
Finally, there's also a Set interface, used when you don't need access by key, and want to use methods like "contains()"
Sets: HashSet, TreeSet, LinkedHashSet
Comments
If you'd like to add something to this, or you want to correct me on something, feel free to leave a comment below or on my twitterpage!
@Qkyrie and David
Remember ArrayList isn't the only List implementation! Choosing the right interface is a first step to choosing the right datastructure, but sometimes a lot of performance can be gained by using another implementation of the chosen interface.
BeantwoordenVerwijderenIf you frequently add elements to the beginning of a List or iterate over the List to delete elements from its interior, you should consider using LinkedList.
Lists: ArrayLists, LinkedList, Vector (synchronised list)
Maps: HashMap, TreeMap, LinkedHashMap
Finally, there's also a Set interface, used when you don't need access by key, and want to use methods like "contains()"
Sets: HashSet, TreeSet, LinkedHashSet
thanks very useful, i want to know Which implementing? my system have a group of words that need to ignore in some prhases, i want to know the more convenient structure to do that
BeantwoordenVerwijderenHi Diego
BeantwoordenVerwijderenWell, I'd play around with the method contains() which is in most collections. I do think that a List would be the best approach for your problem. You should put all the words that need to be ignored in a List - let's call it myList - and then do somethingn like:
for(String s : thePhrases.split[" "])
{
if(!myList.contains(s))
System.out.print(s + " ");
}
Do note that you shouldn't just take this code as it is, it's merely something to learn from. You might want to try to work with sets and Maps (not suggested, you don't have a value, just a key) to check which is faster..
Kind regards
Qkyrie
@DeduXion