Which one is more efficient to instantiate a list ?
List<Type> list = new ArrayList<Type>(2);
list.add(new Type("one"));
list.add(new Type("two"));
OR
List<Type> list = Arrays.asList(new Type("one"), new Type("two"));
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1 Answer
They create different types of objects. new ArrayList<>() creates a java.util.ArrayList, which can be added to, etc.
Arrays.asList() uses a type which happens to also be called ArrayList, but is a nested type (java.util.Arrays$ArrayList) and doesn't allow elements to be added or removed. It just wraps an array.
Now, if you don't care about those differences, you end up with two roughly-equivalent implementations, both wrapping an array in the List<> interface. I would be very surprised to see them differ in performance in any significant way - but as ever, if you have specific performance concerns, you should test them in your particular context.
2 Comments
exception1
Wow, I didn't even know that ArrayList from
Arrays.asList() actually is another ArrayList than the java.util.ArrayList.
ParkerHalo
I didn't know that either... As it seems the 2 variants differ a bit in efficiency (at least on my machine). On 100 million runs the first variant needs ~ 1500 ms and the second ~ 900 ms