i'm sorry stupid question, have been searching how use binarysearch arraylist :
list<integer> arrlist = new arraylist<integer>(); arrlist.add(3); arrlist.add(5); arrlist.add(7); arrlist.add(2); the problem when use :
collections.sort(arrlist); collections.reverse(arrlist); int indeks = collections.binarysearch(arrlist, 7); the value of indeks -5, thought should 2 because after reversing myarrlist output looks :
[7, 5, 3, 2] so should here in order right indeks of 7...? in advance
collections.binarysearch() expects elements in ascending order:
the list must sorted ascending order according natural ordering of elements (as
sort(list)method) prior making call. if not sorted, results undefined.
if want binary search on descending list, use comparator.reverseorder():
int indeks = collections.binarysearch(arrlist, 7, comparator.reverseorder()); indeks 0, corresponding first element of list.
note can use same comparator sort list descending, instead of sorting ascending , reversing:
collections.sort(arrlist, comparator.reverseorder()); 