Sort Objects in Arraylist by Date

Sort objects in ArrayList by date?

You can make your object comparable:

public static class MyObject implements Comparable<MyObject> {

  private Date dateTime;

  public Date getDateTime() {
    return dateTime;
  }

  public void setDateTime(Date datetime) {
    this.dateTime = datetime;
  }

  @Override
  public int compareTo(MyObject o) {
    return getDateTime().compareTo(o.getDateTime());
  }
}

And then you sort it by calling:

Collections.sort(myList);

However sometimes you don't want to change your model, like when you want to sort on several different properties. In that case, you can create comparator on the fly:

Collections.sort(myList, new Comparator<MyObject>() {
  public int compare(MyObject o1, MyObject o2) {
      return o1.getDateTime().compareTo(o2.getDateTime());
  }
});

However, the above works only if you're certain that dateTime is not null at the time of comparison. It's wise to handle null as well to avoid NullPointerExceptions:

public static class MyObject implements Comparable<MyObject> {

  private Date dateTime;

  public Date getDateTime() {
    return dateTime;
  }

  public void setDateTime(Date datetime) {
    this.dateTime = datetime;
  }

  @Override
  public int compareTo(MyObject o) {
    if (getDateTime() == null || o.getDateTime() == null)
      return 0;
    return getDateTime().compareTo(o.getDateTime());
  }
}

Or in the second example:

Collections.sort(myList, new Comparator<MyObject>() {
  public int compare(MyObject o1, MyObject o2) {
      if (o1.getDateTime() == null || o2.getDateTime() == null)
        return 0;
      return o1.getDateTime().compareTo(o2.getDateTime());
  }
});

Sorting list of objects by date property

You can use Collections.sort with a Comparator. In Java 8 with Lambdas it looks like this:

    Collections.sort(list, (x, y) -> x.startDate.compareTo(y.startDate));

    for (int i = 0; i < (list.size() - 1); i++) {
        list.get(i).endDate = list.get(i + 1).startDate;
    }

How to Sort Date in a Custom Arraylist in Android Studio?

You can use below method to sort your list by date.

 Collections.sort(list, (item1, item2) -> {
            Date date1 = stringToDate(item1.getDate());
            Date date2 = stringToDate(item2.getDate());

            if (date1 != null && date2 != null) {
                boolean b1;
                boolean b2;
                if (isAscending) {
                    b1 = date2.after(date1);
                    b2 = date2.before(date1);
                }else {
                    b1 = date1.after(date2);
                    b2 = date1.before(date2);
                }

                if (b1 != b2) {
                    if (b1) {
                        return -1;
                    }
                    if (!b1) {
                        return 1;
                    }
                }
            }
            return 0;
        });

public static Date stringToDate(String strDate) {
        if (strDate == null)
            return null;

        // change the date format whatever you have used in your model class.
        SimpleDateFormat format = new SimpleDateFormat("MMM dd, yyyy hh:mm:ss a", Locale.US);
        Date date = null;
        try {
            date = format.parse(strDate);
            System.out.println(date);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return date;
    }

Sorting arraylist of objects based on the date time

If you meant they have Java Date object. You can just do Collections#sort()

How to sort objects according to string date in java

LocalDate as your property

The best solution is to alter your Customer class to use LocalDate class as the type of your property.

Tip: Use a more descriptive name for your member fields that just date.

public class Customer {
    public LocalDate firstContact ; 
    …
}

Now your Comparator becomes quite simple, as the LocalDate class already implements the Comparable interface and its compareTo method.

public static Comparator< Customer > CustomerComparator = new Comparator< Customer >() 
{
    @Override
    public int compare( Customer c1 , Customer c2 ) {
        return ( c1.firstContact.compareTo( c2.firstContact ) ) ;
    }
};

If you cannot change the data type of your class property, see the correct Answer by Ezequiel.

Sorting objects of ArrayList by their date and time

I’m assuming your Appointment class looks something like this:

class Appointment {
    private int patientId;
    private LocalDateTime appointmentDate;

    // Getters & setters
}

If so, you’d create a Comparator to sort using the Comparator.comparing method:

ArrayList<Appointment> appointments = new ArrayList<>();

Collections.sort(appointments, Comparator.comparing(appointment -> {
    return appointment.getAppointmentDate();
}));

That lambda function tells the comparator how to take your object (an Appointment) and extract the element used to sort (the key; appointmentDate). It can be condensed down to a method reference if you like:

Collections.sort(appointments, Comparator.comparing(Appointment::getAppointmentDate));

You can also call Collection#sort() directly on the ArrayList:

appointments.sort(Comparator.comparing(Appointment::getAppointmentDate));

---

If you’re always (or usually) going to sort your Appointment objects by date, you might consider making Appointment implement Comparable so that you can call .sort() without passing a Comparator:

class Appointment implements Comparable<Appointment> {
    private int patientId;
    private LocalDateTime appointmentDate;

    // Getters & setters

    @Override
    public int compareTo(final Appointment other) {
        return appointmentDate.compareTo(other.appointmentDate);
    }
}

How to sort a list of objects by date when date is String?

I think that you can create a custom comparator with an structure similar to the below:

Collections.sort(datestring, new Comparator<String>() {
    DateFormat df = new SimpleDateFormat("your format");
    @Override
    public int compare(String s1, String s2) {
       try {
            return df.parse(s1).compareTo(df.parse(s2));
        } catch (ParseException e) {
            throw new IllegalArgumentException(e);
        }
    }
});

---

Related Topics