collections - java.lang.IllegalArgumentException: Comparison method violates its general contract (not reproducible) -

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• comparison method violates general contract exception 1 answer

i trying reproduce exception (java.lang.illegalargumentexception: comparison method violates general contract!) need debug piece of code, code below never throws it,

try {   arraylist al = new arraylist();   (int = 1; <= 36; i++) {     typeadaptersort t = new typeadaptersort();     t.order = i;     al.add(t);   }   system.out.println(al.size());   collections.sort(al, new comparator() {     public int compare(object o1, object o2) {       typeadaptersort tas1 = (typeadaptersort) o1;       typeadaptersort tas2 = (typeadaptersort) o2;       if (tas1.order < tas2.order)         return -1;       else         return 1;     }   });  } catch (exception e) {   system.out.println(e); } 

also, when checked jdk code seems exception thrown collections.sort method when size of collection sorted greater 32?. change should made in code block collections.sort throws exception.

this problem

if (tas1.order < tas2.order)     return -1; else     return 1; 

if order equal you'll different result depending on goes comparator first, not right.

the contract if < b , b < c < c, in case can broken depending order arguments passed.

try like

return tas1.order -tas2.order; 

this explains why can't reproduce test data never has duplicates. try adding dupes in test data , see if can reproduce (before applying fix obviously...)