I want to sort the objects, and I have applied the approach two ways, however none works. When printing the the content of the arraylist, the elements are in the order they were inserted, and not lexicographically sorted.

I did do research within stackoverlow:

1. 

   In case it works and you want an explanation on anything, I can try to explain it in details! I hope it helps.

   CodePudding user response：

   You can try adding this code to your sortPue() method:

   public void sortPue() {
       Collections.sort(pue_ArrayList,
           new Comparator<Pue>()
           {
               public int compare(Pue pp1, Pue pp2)
               {
                   return pp1.toString().compareTo(pp2.toString());
               }        
           });
   }
   

   When implementing Comparator, you have to specify the types you want to compare, in this case there is <Pue>. Then, we have to add an implementation for the compare method, passing two object references to be compared. In the end, String's compareTo method is used to sort the list.

   Collections.sort takes 2 parameters:

   • the list to be sorted;
   • the comparator to determine the order of the list. A null value indicates that the elements' natural ordering should be used.

   String compareTo returns:

   • the value 0 if the argument string is equal to this string;
   • a value less than 0 if this string is lexicographically less than the string argument;
   • a value greater than 0 if this string is lexicographically greater than the string argument.

   CodePudding user response：

   At a quick glance, this is probably the source of the problem.

       Pue tempPue = pue_ArrayList.get(i);
   
       pue_ArrayList.set(i, pue_ArrayList.get(j));
       
       pue_ArrayList.set(i, tempPue);
       
   

   So you take out the i'th element, set the i'th element to something else, then set the i'th element back to what it was. Net result: nothing changed.

   Likely that last use of 'i' should be 'j', but I did not analyze this in any detail.