CODEWITHSUNDEEP
javaperformanceobjectarraylist
Svitlana Onish
Svitlana Onish

Reputation: 284

What is faster with item manipulation in Java ArrayList?

I have to replace an element in an ArrayList. Which is faster—using remove() and add() or getting the needed item index and using set(int, E)?

If you know some books about similiar themes, please give me some advice.

Upvotes: 1

Views: 504

Answers (3)

Lucas Santos
Lucas Santos

Reputation: 170

The remove(Object) will perform a linear search in your ArrayList and then remove the first occurrence of the specified object, which means that in the worst case you'll get an O(N) complexity.

If you already know the index to replace, for sure will be faster to call .set(index, object), but if you don't, there is no difference because in both cases you will have to perform a linear search getting O(N) complexity.

add(Object) always add the object at the end of the ArrayList, so it runs in O(1) complexity to add a single object in your ArrayList.

Upvotes: 1

assylias
assylias

Reputation: 328598

It's all in the javadoc (emphasis mine):

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).

To recap: set = O(1) whereas add/remove = O(n) ==> use set.

Upvotes: 2

Yevhen Surovskyi
Yevhen Surovskyi

Reputation: 961

If this is the last item of ArrayList, almost no difference. In othe case - set(int, E) will be faster because no nee to copy part of array

Upvotes: 2

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