java - Sorting cusom type in Set (Set<MyType>) -

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• is collections.sort method used list type of collections? 7 answers

why can't collections.sort set<mytype>? code below. when use arraylistthis code works perfectly, when use kind of set, error.

set<auto> set = new hashset<auto>();  set.add(auto1); set.add(auto2); set.add(auto3); set.add(auto4); set.add(auto5);  collections.sort(set, new comparator<auto>() {     @override     public int compare(auto o1, auto o2) {         return o1.getmarka().compareto(o2.getmarka());     } }); 

hashset not ordered collection; in other words, not contain elements in order.

you can see hashset bag contains objects. when stick hand in , pull out objects 1 one, don't know in order elements out. can't sort elements in bag - because bag doesn't keep them in order sorted them in.

the order of elements lost; sorting hashset has no effect (besides fact collections.sort takes list instead of set mureinik noticed, code doesn't compile).

if need elements in set in specific, defined order, use different set implementation, example treeset.