Sort ArrayList w.r.t Date in java

Question

I am trying to sort ArrayList w.r.t termDate ArrayList contains firstName,lastName,email,startDate,termDate

Dates can be either empty or null. I have to compare accordingly and put all the null/empty date values at the end.

Collections.sort(usersList, new Comparator<User>() {
                public int compare(User o1, User o2) {
                    if(o1.getTermDate() == null && o2.getTermDate() == null)
                        return 0; //They are both null, both equal
                    if(o1.getTermDate() == null && o2.getTermDate() != null)
                        return -1; // The first is null and the second is not, return the first as lower than the second
                    if(o1.getTermDate() != null && o2.getTermDate() == null)
                        return 1; //The first is not null and the second is, return the first as higher than the second
                    else
                        return o1.getTermDate().compare(o2.getTermDate()); //Return the actual comparison
                }
            });

It is not compiling compare method.

Please guide.

@Tunaki thanks. compareTo is not giving compilation issues. do i need to pass the Collections.sort(..) to ArrayList again or the existing userList will be sorted and I can access it? — prashanth
– prashanth, Commented Aug 25, 2015 at 13:42
Collections.sort sorts the list in-place. That means the list given as argument will be sorted after the call to this method. — Tunaki
– Tunaki, Commented Aug 25, 2015 at 13:48
@Tunaki I don't understand why it is not swapping in my case. i have put sysouts to check Term Date: null 2015-08-31 00:00:00.0 Term Date2: -1 null 2015-08-31 00:00:00.0 Term Date: 2015-08-31 00:00:00.0 2015-12-31 00:00:00.0 Term Date4: 2015-08-31 00:00:00.0 2015-12-31 00:00:00.0 Term Date: 2015-12-31 00:00:00.0 null Term Date3: 1 2015-12-31 00:00:00.0 null Term Date: 2015-08-31 00:00:00.0 null Term Date3: 1 2015-08-31 00:00:00.0 null Term Date: null null Term Date1: 0 null null — prashanth
– prashanth, Commented Aug 25, 2015 at 14:41

kai · Accepted Answer · 2015-08-25 13:37:48Z

1

You should change return o1.getTermDate().compare(o2.getTermDate()); to return o1.getTermDate().compareTo(o2.getTermDate()); Because the class java.util.Date; has not method called compare.

answered Aug 25, 2015 at 13:37

kai

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