Re: Cost of creating objects?

Eric Sosman <esosman@comcast-dot-net.invalid>
Wed, 07 Aug 2013 20:51:52 -0400
On 8/7/2013 7:52 PM, Lew wrote:

Eric Sosman wrote:

Sebastian wrote:

[...] The reason I asked is we have a person in our group
who is very much in a micro-optimization mind-set. Among the things
that concern him are, for example, temporary local variables, wrappers
as method arguments wasting heap space compared to primitives,
multiple hash map lookups (containsKey() followed by get()) etc.

Overrule him. He's an idiot. Although doing a 'containsKey()' before a 'get()' is silly.

     Situation: A Map that is searched for keys that are usually
*not* present (poor man's Bloom filter, say), and some of whose
mapped values are null. Now, attend:

    if (map.containsKey(key)) { // usually false
        Value val = map.get(key); // seldom needed


    Value val = map.get(key);
    if (val == null // usually true
        || map.containsKey(key) // usually false
    ) {

If the key is present 0.0 <= p <= 1.0 of the time, the first
version does (1 + p) searches, the second (1 + (1 - p)) = (2 - p).
Even if the second search is cheaper than the first (maybe the
key's hashCode has been cached), for small p the first wins.

Eric Sosman

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