title: Why is Collections.sort() much slower than Arrays.sort()?
body: <p>I tried to do a test, regarding <code>Collection.sort()</code> and <code>Arrays.sort()</code>. In the test, I created an array of <code>int</code>s of length <code>1e5</code> 100 times, which contained random numbers from 1 to 1e5. I also created a list of type <code>Integer</code>, which contained the same values at the same positions as that of the array. Then I sorted the array using <code>Arrays.sort()</code> and the list using <code>Collections.sort()</code>. </p>
  
  <hr>
  
  <p><strong>UPDATE:</strong> As @Holger pointed out, my code had a bug. The corrected code is now:</p>
  
  <pre><code>import java.util.* ;
  
  
  class TestClass {
      public static void main(String args[] ) throws Exception {
          double ratSum = 0 ;
          for(int j=0;j&lt;100;j++)
          {
          int[] A = new int[(int)1e5] ;
          List&lt;Integer&gt; L = new ArrayList&lt;Integer&gt;() ;
          for(int i=0;i&lt;A.length;i++)
          {
              int no = (int)(Math.random()*(int)1e5) ;
              A[i] = no ;
              L.add(A[i]) ;
          }
  
          long startTime = System.nanoTime() ;
          Arrays.sort(A) ;
          long endTime = System.nanoTime() ;
          Collections.sort(L) ;
          long endTime2 = System.nanoTime() ;
          long t1 = (endTime-startTime), t2 = (endTime2-endTime) ;
          ratSum+=(double)t2/t1 ;
          System.out.println("Arrays.sort took :"+t1+" Collections.sort took :"+t2+" ratio :"+((double)t2/t1)) ;
      }
      System.out.println("Average ratio :"+(ratSum/100)) ;
      }
  }
  </code></pre>
  
  <p>And the output is:</p>
  
  <pre><code>Arrays.sort took :24106021 Collections.sort took :92353602 ratio :3.8311425182944956
  Arrays.sort took :8672831 Collections.sort took :50936497 ratio :5.873110752417521
  Arrays.sort took :8561227 Collections.sort took :25611480 ratio :2.991566512603859
  Arrays.sort took :7123928 Collections.sort took :17368785 ratio :2.4380910362934607
  Arrays.sort took :6280488 Collections.sort took :16929218 ratio :2.6955258890710403
  Arrays.sort took :6248227 Collections.sort took :16844915 ratio :2.695951187432851
  Arrays.sort took :6220942 Collections.sort took :16979669 ratio :2.7294369566538315
  Arrays.sort took :6213841 Collections.sort took :17439817 ratio :2.8066081832476883
  Arrays.sort took :6286385 Collections.sort took :19963612 ratio :3.175690321225951
  Arrays.sort took :6209668 Collections.sort took :17008307 ratio :2.7390042430609816
  Arrays.sort took :6286623 Collections.sort took :17007163 ratio :2.705293923303497
  Arrays.sort took :6256505 Collections.sort took :16911950 ratio :2.703098614961548
  Arrays.sort took :6225031 Collections.sort took :16914494 ratio :2.7171742598550916
  Arrays.sort took :6233918 Collections.sort took :17005995 ratio :2.72797861633727
  Arrays.sort took :6210554 Collections.sort took :17606028 ratio :2.834856278522013
  Arrays.sort took :6239384 Collections.sort took :20342378 ratio :3.260318326296314
  Arrays.sort took :6207695 Collections.sort took :16519089 ratio :2.6610664666997974
  Arrays.sort took :6227147 Collections.sort took :16605884 ratio :2.666692146499834
  Arrays.sort took :6225187 Collections.sort took :16687597 ratio :2.680657946500242
  Arrays.sort took :6152338 Collections.sort took :16475373 ratio :2.6779043999208105
  Arrays.sort took :6184746 Collections.sort took :16511024 ratio :2.6696365541931715
  Arrays.sort took :6130221 Collections.sort took :16578032 ratio :2.7043122915144493
  Arrays.sort took :6271927 Collections.sort took :16507152 ratio :2.631910734930429
  Arrays.sort took :6232482 Collections.sort took :16562166 ratio :2.657394919070765
  Arrays.sort took :6218992 Collections.sort took :16552468 ratio :2.661599821964717
  Arrays.sort took :6230427 Collections.sort took :21954967 ratio :3.52383022865046
  Arrays.sort took :8204666 Collections.sort took :16607560 ratio :2.024160398485447
  Arrays.sort took :6272619 Collections.sort took :22061291 ratio :3.5170781136236715
  Arrays.sort took :8618253 Collections.sort took :19979549 ratio :2.3182829513127543
  Arrays.sort took :6198538 Collections.sort took :17002645 ratio :2.743008915973412
  Arrays.sort took :6265018 Collections.sort took :17079646 ratio :2.7261926462142645
  Arrays.sort took :6302335 Collections.sort took :17040082 ratio :2.7037728080148073
  Arrays.sort took :6293948 Collections.sort took :17133482 ratio :2.722215372608735
  Arrays.sort took :6272364 Collections.sort took :17099717 ratio :2.7261997231028046
  Arrays.sort took :6219540 Collections.sort took :17026849 ratio :2.737637992520347
  Arrays.sort took :6231000 Collections.sort took :17149439 ratio :2.7522771625742255
  Arrays.sort took :6309215 Collections.sort took :17118779 ratio :2.713297771592821
  Arrays.sort took :6200511 Collections.sort took :17123517 ratio :2.7616299688848227
  Arrays.sort took :6263169 Collections.sort took :16995685 ratio :2.7135919532109063
  Arrays.sort took :6212243 Collections.sort took :17101848 ratio :2.7529264389689843
  Arrays.sort took :6247580 Collections.sort took :17089850 ratio :2.735435160494143
  Arrays.sort took :6283626 Collections.sort took :17088109 ratio :2.7194662763188004
  Arrays.sort took :6312678 Collections.sort took :17055856 ratio :2.7018415955954036
  Arrays.sort took :6222695 Collections.sort took :17071263 ratio :2.7433873908330715
  Arrays.sort took :6300990 Collections.sort took :17016171 ratio :2.7005551508572463
  Arrays.sort took :6262923 Collections.sort took :17084477 ratio :2.727875945465081
  Arrays.sort took :6256482 Collections.sort took :17062232 ratio :2.7271287602202006
  Arrays.sort took :6259643 Collections.sort took :17036036 ratio :2.721566709155778
  Arrays.sort took :6248649 Collections.sort took :16944960 ratio :2.711779778316881
  Arrays.sort took :6264515 Collections.sort took :16986876 ratio :2.7116027338109974
  Arrays.sort took :6241864 Collections.sort took :17367903 ratio :2.782486609769133
  Arrays.sort took :6297429 Collections.sort took :17080086 ratio :2.7122316107097038
  Arrays.sort took :6184084 Collections.sort took :17584862 ratio :2.843567778186713
  Arrays.sort took :6315776 Collections.sort took :22279278 ratio :3.5275598754610678
  Arrays.sort took :6253047 Collections.sort took :17091694 ratio :2.7333384828228544
  Arrays.sort took :6291188 Collections.sort took :17147694 ratio :2.725668665441249
  Arrays.sort took :6327348 Collections.sort took :17034007 ratio :2.6921242517402235
  Arrays.sort took :6284904 Collections.sort took :17049315 ratio :2.712740719667317
  Arrays.sort took :6190436 Collections.sort took :17143853 ratio :2.7694096183209065
  Arrays.sort took :6301712 Collections.sort took :17070237 ratio :2.7088253160411013
  Arrays.sort took :6208193 Collections.sort took :17060372 ratio :2.74804149935416
  Arrays.sort took :6247700 Collections.sort took :16961962 ratio :2.7149130079869392
  Arrays.sort took :6344996 Collections.sort took :17084627 ratio :2.6926143058246215
  Arrays.sort took :6214232 Collections.sort took :17150324 ratio :2.759846108095095
  Arrays.sort took :6224359 Collections.sort took :17081254 ratio :2.744259127727048
  Arrays.sort took :6256722 Collections.sort took :17005451 ratio :2.7179489515436357
  Arrays.sort took :6286439 Collections.sort took :17061112 ratio :2.713954911516679
  Arrays.sort took :6250634 Collections.sort took :17091313 ratio :2.7343327092899696
  Arrays.sort took :6252900 Collections.sort took :17041659 ratio :2.7254008540037424
  Arrays.sort took :6222192 Collections.sort took :17125062 ratio :2.75225547524088
  Arrays.sort took :6227037 Collections.sort took :17013314 ratio :2.7321684454420296
  Arrays.sort took :6223609 Collections.sort took :17086112 ratio :2.745370411283871
  Arrays.sort took :6280777 Collections.sort took :17091821 ratio :2.7212908530266238
  Arrays.sort took :6254551 Collections.sort took :17148242 ratio :2.741722307484582
  Arrays.sort took :6250927 Collections.sort took :17053331 ratio :2.7281283240069834
  Arrays.sort took :6270616 Collections.sort took :17067948 ratio :2.721893351466586
  Arrays.sort took :6223093 Collections.sort took :17034584 ratio :2.737317922132933
  Arrays.sort took :6286002 Collections.sort took :17128280 ratio :2.7248289135129133
  Arrays.sort took :6239485 Collections.sort took :17032062 ratio :2.7297224049741287
  Arrays.sort took :6191290 Collections.sort took :17017219 ratio :2.748574045150526
  Arrays.sort took :6134110 Collections.sort took :17069485 ratio :2.782715830006309
  Arrays.sort took :6207363 Collections.sort took :17052862 ratio :2.747199092432648
  Arrays.sort took :6238702 Collections.sort took :17056945 ratio :2.734053493819708
  Arrays.sort took :6185356 Collections.sort took :17006088 ratio :2.749411351585907
  Arrays.sort took :6309226 Collections.sort took :17056503 ratio :2.703422416632405
  Arrays.sort took :6256706 Collections.sort took :17082903 ratio :2.7303349398229675
  Arrays.sort took :6194988 Collections.sort took :17069426 ratio :2.7553606237816766
  Arrays.sort took :6184266 Collections.sort took :17054641 ratio :2.757746998592881
  Arrays.sort took :6271022 Collections.sort took :17086036 ratio :2.724601508334686
  Arrays.sort took :6246482 Collections.sort took :17077804 ratio :2.733987546910405
  Arrays.sort took :6194985 Collections.sort took :17119911 ratio :2.763511291794895
  Arrays.sort took :6319199 Collections.sort took :17444587 ratio :2.760569337980969
  Arrays.sort took :6262827 Collections.sort took :17065589 ratio :2.7249018693954024
  Arrays.sort took :6301245 Collections.sort took :17195611 ratio :2.728922776371971
  Arrays.sort took :6214333 Collections.sort took :17024645 ratio :2.739577199998777
  Arrays.sort took :6213116 Collections.sort took :17382033 ratio :2.7976353572024086
  Arrays.sort took :6286394 Collections.sort took :17124874 ratio :2.7241171965995132
  Arrays.sort took :6166308 Collections.sort took :16998293 ratio :2.756640278104824
  Arrays.sort took :6247395 Collections.sort took :16957056 ratio :2.7142602636779007
  Arrays.sort took :6245054 Collections.sort took :16994147 ratio :2.72121698227109
  Average ratio :2.792654880602193
  </code></pre>
  
  <p>Moreover, I ran the code locally, 1000 times (instead of 100) and the average ratio was: :3.0616
  So, the ratio is still significant and thus worthy of discussion.</p>
  
  <p><strong>Question:</strong>
  Why does <code>Collections.sort()</code> take approximately 3 times of the time taken by <code>Arrays.sort()</code> to sort the same values?
  Is it because now we're not comparing primitives? Why would that take more time?</p>