Sorting Values of Set

Question

I am trying to sort elements of a set but unable to do so far  here is my code which i am trying to do  public static void main String    args       Set lt String gt  set new HashSet lt String gt         set add  12        set add  15        set add  5        List lt String gt  list asSortedList set      public static  lt T extends Comparable lt   super T gt  gt  List lt T gt  asSortedList Collection lt T gt  c      List lt T gt  list   new ArrayList lt T gt  c     Collections sort list     return list      but this or other way is not working since its all time giving me the same order in which they have been filled 12 15 5

User · Accepted Answer

If you sort the strings  12    15  and  5  then  5  comes last because  5     1   i e  the natural ordering of Strings doesn t work the way you expect   If you want to store strings in your list but sort them numerically then you will need to use a comparator that handles this  e g   Collections sort list  new Comparator lt String gt          public int compare String o1  String o2            Integer i1   Integer parseInt o1           Integer i2   Integer parseInt o2           return  i1  gt  i2   -1    i1    i2   0   1                Also  I think you are getting slightly mixed up between Collection types  A HashSet and a HashMap are different things

User · Answer

You need to pass in a Comparator instance to the sort method otherwise the elements will be sorted in their natural order   For more information check Collections sort List  Comparator

User · Answer

Use the Integer wrapper class instead of String because it is doing the hard work for you by implementing Comparable lt Integer gt   Then java util Collections sort list   would do the trick

User · Answer

Use a SortedSet  TreeSet is the default one    SortedSet lt String gt  set new TreeSet lt String gt     set add  12    set add  15    set add  5    List lt String gt  list new ArrayList lt String gt  set     No extra sorting code needed   Oh  I see you want a different sort order  Supply a Comparator to the TreeSet   new TreeSet lt String gt  Comparator comparing Integer  valueOf      Now your TreeSet will sort Strings in numeric order  which implies that it will throw exceptions if you supply non-numeric strings   Reference    Java Tutorial  Collections Trail     Object Ordering The SortedSet interface  Javadocs  TreeSet Javadocs  Comparator

User · Answer

You re using the default comparator to sort a Set lt String gt   In this case  that means lexicographic order  Lexicographically   12  comes before  15   comes before  5    Either use a Set lt Integer gt    Set lt Integer gt  set new HashSet lt Integer gt     set add 12   set add 15   set add 5     Or use a different comparator   Collections sort list  new Comparator lt String gt          public int compare String a  String b            return Integer parseInt a  - Integer parseInt b

User · Answer

Strings are sorted lexicographically   The behavior you re seeing is correct   Define your own comparator to sort the strings however you prefer   It would also work the way you re expecting  5 as the first element  if you changed your collections to Integer instead of using String

[java] Sorting Values of Set

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