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Key existence check in HashMap

Asked 2010-09-02T11:45:16.013
383

Is checking for key existence in HashMap always necessary?

I have a HashMap with say a 1000 entries and I am looking at improving the efficiency. If the HashMap is being accessed very frequently, then checking for the key existence at every access will lead to a large overhead. Instead if the key is not present and hence an exception occurs, I can catch the exception. (when I know that this will happen rarely). This will reduce accesses to the HashMap by half.

This might not be a good programming practice, but it will help me reduce the number of accesses. Or am I missing something here?

[Update] I do not have null values in the HashMap.

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2 Answers

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Just use containsKey() for clarity. It's fast and keeps the code clean and readable. The whole point of HashMaps is that the key lookup is fast, just make sure the hashCode() and equals() are properly implemented.

answered 2010-09-02T13:25:35.123
0
  1. If key class is your's make sure the hashCode() and equals() methods implemented.
  2. Basically the access to HashMap should be O(1) but with wrong hashCode method implementation it's become O(n), because value with same hash key will stored as Linked list.
answered 2010-09-02T12:02:21.873

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