[Solved] How does the Comparator works with Arrays.sort?

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Rules for a.compareTo(b)

  • returns negative value : a is before b
  • returns 0 : a equal to b
  • return positive value : a is after b

Because the parameter are first, second and you compare like second.compareTo(first) you’ll get reverse order : 

(second+first)   344 first+ second  434 comparing : -1 >>   4 is before 34
(second+first)   423 first+ second  234 comparing : 2  >>  23 is after   4
(second+first)  3423 first+ second 2334 comparing : 1  >>  23 is after  34
(second+first)  3415 first+ second 1534 comparing : 2  >>  15 is after  34
(second+first)  2315 first+ second 1523 comparing : 1  >>  15 is after  23

With these 5 before/after rules the order is 4 34 23 15

Which is Reverse Lexical Order (Lexical because use of String, reverse because compare second to first)

Details for one case

  • The sort method will compare 4 and 34, so first=4 and second=34
  • you compute "344".compareTo("434"), because 344 is before 434 is lexical order you got -1
  • Because of -1 the sort method will remember that 4 is before 34

solved How does the Comparator works with Arrays.sort?