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Time Complexity of HashMap.toArray()

Mike Broadbear
Ranch Hand

Joined: Jan 14, 2002
Posts: 39
I was wondering if anyone knows the time complexity of a HashMap.toArray() operation.

...Mike B.
Henry Wong
author
Sheriff

Joined: Sep 28, 2004
Posts: 18847
    
  40

First, I am assuming that you mean get a Set first, as Maps don't have a toArray() method.

If memory serves, I believe it is just a simple loop with an iterator to fill an newly created array -- so it should be O(n).

Henry


Books: Java Threads, 3rd Edition, Jini in a Nutshell, and Java Gems (contributor)
Rob Spoor
Sheriff

Joined: Oct 27, 2005
Posts: 19697
    
  20

I don't think it can be done more efficiently. In the end, all elements need to be copied to the new array. While an ArrayList could possibly do it faster because it can use native code like System.arraycopy and perhaps even cloning its array, that still copies all elements.


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