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java Program runtime is too fast? Issue with Memory

So I am running some simulations that require some sample datasets. For the sake of simplicity I am using this http://loremipsum.sourceforge.net/ Lorem Ipsum generator. I am setting a test parameter called DATASIZE that sets the amount of words or paragraphs this generator creates. I am using this generated data to create an “input” and “output” hash. The output data will use a slightly different hash. For example,

String input = hash(new LoremIpsum().getWords(DATASIZE))
String output = hash(new LoremIpsum().getWords(DATASIZE-2))

My question is, does Java keep the first data set in memory and then slightly modify it to quickly produce output? Maybe I was just pessemistic on the runtime but it seems very small. Virtually zero in System.currentTimeMillis(); Could it be the jar?

I also noticed something odd with my output. I am creating several objects that store this input and output hash. On some of these that I generate, for some reason the runtime is 16. Otherwise it is 0. Something with memory or just shoddy code?

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Answer

It uses StringBuilder. So answer to your question is NO. There is no reuse/cache in getWords(..). – https://sourceforge.net/p/loremipsum/code/HEAD/tree/trunk/src/main/java/de/svenjacobs/loremipsum/LoremIpsum.java

Having said that, if you give really large number – say 1000000 then you may see difference. I checked using my latest all powerful macbook pro

public static void main(String[] args) {
    LoremIpsum loremipsum = new LoremIpsum();
    
    long start;
    int number = 100000;
    
    for(int i=0;i<5;i++) {
        start = System.currentTimeMillis();
        loremipsum.getWords(number);
        System.out.println("getWords():" +(System.currentTimeMillis()-start));
    }

}

Output in ms

getWords():11
getWords():7
getWords():5
getWords():4
getWords():4
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