Java collection insertion: Set vs. List

Question

I\'m thinking about filling a collection with a large amount of unique objects. How is the cost of an insert in a Set (say HashSet) compared to an List (say ArrayList)?

Answer 1

I don't think you can make this judgement simply on the cost of building the collection. Other things that you need to take into account are:

• Is the input dataset ordered? Is there a requirement that the output data structure preserves insertion order?
• Is there a requirement that the output data structure is ordered (or reordered) based on element values?
• Will the output data structure be subsequently modified? How?
• Is there a requirement that the output data structure is duplicate free if other elements are added subsequently?
• Do you know how many elements are likely to be in the input dataset?
• Can you measure the size of the input dataset? (Or is it provided via an iterator?)
• Does space utilization matter?

These can all effect your choice of data structure.