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I'm trying to solve the following problem:
I have some expensive work to do which I then cache the result of
The work is keyed by a string
Many requests may arrive simultaneously for the same key
I'd like to avoid doing the work more than once per key
I'd like to add callbacks against the key which will be invoked when the work is completed; not all of these are known when the work is first submitted.
This feels like a problem which ought to have been solved already; does anybody know of a Java framework or library which covers it?
I can imagine a wrapper around guava's LoadingCache but I'm not aware of a library which does everything out of the box.
While LoadingCache#get is synchronous, it does get you 1-4 and there may be some mileage in using refresh which can return a ListenableFuture (although to get all the features you list it might become a fairly chunky wrapper?)
For Reference:
http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/cache/LoadingCache.html#refresh(K)
http://www.theotherian.com/2013/11/non-blocking-cache-with-guava-and-listenable-futures.html
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In a recent interview with Amazon I have been rejected because I could not tell the advantage and disadvantage of making model and Entity classes different and same.
I have always created Model and Entity class same.
Can anybody help me on that with an example? Interviewer said you are making strong binding of UI+DB if you are keeping it same.
It's true by making same class for Entity and Model you are tightly binding UI and DB, simple example of why should avoid is -> most of the time, we modify response like adding DTO, modifying format of date and so on. which could impact your database calls (DTO layer).you can read more here
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I was reading about Garbage Collector performance and found the term max-jOPS and critical jOPS.
Link: http://openjdk.java.net/jeps/333
Can someone tell the full form and explain what is it?
These (jOPS, max-jOPS and critical-jOPS) are not GC terms.
I believe that you are referring to the terminology used in the SPECjbb2015 Benchmark; e.g. https://www.spec.org/jbb2015/docs/userguide.pdf. (This is confirmed by your update.)
The documents about the benchmark that I read don't specifically say what jOPS stands for. However the Glossary says that OPS stands for Operations Per Second, and I infer from the context that the j refers to jbb2015.
In other words, jOPS represents the rate at which a "unit of work" is performed by the jbb2015 benchmark. The unit is artificial, and is not designed to directly map to any real world measures ... though there will often be a correlation.
And the max-jOPS and critical-jOPS are specific points in the RT (Response-Throughput) curve that the benchmark captures.
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I'm looking for a Java/Android implementation of promises that allow chaining and joining.
With chaining I mean chaining then calls so code looks like synchronous.
// Example:
getCity().then(getRestaurants).then(findBestMenu);
With joining I mean waiting for multiple promises to be fulfilled, or any of them fail.
// Example:
Promise p1 = getFlights();
Promise p2 = getHotels();
PromiseManager.when(p1,p2).then(planTrip).fail(stayAtHome);
I have found these solutions:
RxJava-Promises supports chaining via PromiseFunction and RepromiseFunction.
jdeferred supports joining via DeferredManager. EDIT: It also supports chaining via DonePipe.
EDIT2:
RxJava or RxAndroid are for reactive paradigm. A bit more complex but powerful.
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I am a complete newbie to Java programming and I am trying to learn caching and hash tables. I have seen tutorials online but they are complex, does anyone here know of any relatively short programs that utilise caching and hash tables?
Thanks for any help given
UPDATE:
I am basically starting from scratch. I know hash tables and sort of know caching (more simple caching programs would be much appreciated), but I don't get how the two work together. For example saving to a hash table and caching the data.
As the comments mention, a cache is just a store where you keep the output so you won't have to do the calculation again.
Here's a really simple example
Map<String,Double> answers = new HashMap<String,Double>();
// checking cache if we have the answer
If (answers.get("volatility") != null) {
System.out.println("volatility found in cache:" +
answers.get("volatility"));
}
// store a value in cache
answers.put("rate",1.887);
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I want to match regular expressions very fast, low overhead. And I want to be able to choose between multiple expressions.
E.g.
AB* -> case A
XXX -> case B
etc
So I want to name all of which cases matched.
The problem is very similar to a lexical analyzer but the patterns are dynamic. That is, a user could change them at any time. So I don't have the luxuary of re-running Lex. Plus, I could have any number of different matchers.
I don't need any of the subpattern identification/capture stuff in Java or the overhead.
Just need to know which cases matched.
I could write software to do this efficiently...but it would almost be like re-writing lex.
Are there any tools that can do this?
Are there any more efficient regular expression libraries than the built in ones in java? Thread safe, etc.
thanks.