Sort List based on String DateTime

Question

I want to sort list descending based on UTC DateTime which is in String form.

My Class

    data class CartEntity( val itemId: String,  var itemName: String, var createdDate: String)

in this createdDate is "2020-07-28T14:28:52.877Z"

What I have tried

    const val UTC_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"

    Collections.sort(list, object : Comparator<CartEntity> {
        var f: DateFormat =
            SimpleDateFormat(
                AppConstants.UTC_FORMAT, Locale.ENGLISH
            )
    
        override fun compare(o1: CartEntity?, o2: CartEntity?): Int {
            return try {
                val firstitem = f.parse(o1?.createdDate!!)
                val seconditem = f.parse(o2?.createdDate!!)
                firstitem.compareTo(seconditem)
            } catch (e: ParseException) {
                throw IllegalArgumentException(e)
            }
        }
    
    })

But still sort by descending is not working as expected

Answer 1

In kotlin style, you can use the standard library functions (following idioms):

Create a new sorted list out of the list you wanna sort:

fun main() {
    val list = listOf<CartEntity>(
        CartEntity(itemId = "", itemName = "", createdDate = "2020-07-28T14:28:52.877Z"),
        CartEntity(itemId = "", itemName = "", createdDate = "2020-09-28T14:28:52.877Z"),
        CartEntity(itemId = "", itemName = "", createdDate = "2020-08-28T14:28:52.877Z"),
        CartEntity(itemId = "", itemName = "", createdDate = "2020-04-28T14:28:52.877Z"),
    )

    val format: DateFormat = SimpleDateFormat(AppConstants.UTC_FORMAT, Locale.ENGLISH)

    val sortedList = list.sortedByDescending { format.parse(it.createdDate) }

    println(sortedList)  // `sortedList` is sorted out list, the `list` is holding the original order
}

Sort the original list (List should be mutable):

fun main() {
    val list = mutableListOf<CartEntity>(
        CartEntity(itemId = "", itemName = "", createdDate = "2020-07-28T14:28:52.877Z"),
        CartEntity(itemId = "", itemName = "", createdDate = "2020-09-28T14:28:52.877Z"),
        CartEntity(itemId = "", itemName = "", createdDate = "2020-08-28T14:28:52.877Z"),
        CartEntity(itemId = "", itemName = "", createdDate = "2020-04-28T14:28:52.877Z"),
    )

    val format: DateFormat = SimpleDateFormat(AppConstants.UTC_FORMAT, Locale.ENGLISH)
    list.sortByDescending { format.parse(it.createdDate) }

    println(list)  // `list` is sorted out list
}

Answer 2

This could be done using following approach.

import java.time.ZonedDateTime;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class Tester {

    static class Car {

        private String date;

        String getDate() {
            return this.date;
        }

        void setDate(String date) {
            this.date = date;
        }

        @Override
        public String toString() {
            return date;
        }

        // Imagine if you keep date not as strings
        ZonedDateTime toDateTime(){
            return ZonedDateTime.parse(this.date);
        }
    }

    public static void main(String[] args) {

        Car first = new Car();
        first.setDate("2020-07-28T14:28:52.877Z");

        Car second = new Car();
        second.setDate("2010-07-28T14:28:52.877Z");

        Car third = new Car();
        third.setDate("2021-07-28T14:28:52.877Z");

        List<Car> cars = Arrays.asList(first, second, third);

        List<Car> sorted = cars.stream().sorted(Comparator.nullsLast(
                (current, next) -> {
                    ZonedDateTime currentDate = ZonedDateTime.parse(current.getDate());
                    ZonedDateTime nextDate = ZonedDateTime.parse(next.getDate());

                    return nextDate.compareTo(currentDate);
                })).collect(Collectors.toList());
    }
}

If you keep the date as regular Date object it will be easier to work with them and the code above could be simplified a bit.

List<Car> sorted = cars.stream()
                               .sorted(Comparator.comparing(Car::toDateTime, Comparator.nullsLast(Comparator.reverseOrder())))
                               .collect(Collectors.toList());

Answer 3

Your code works pretty much fine @Charwaka.

data class CartEntity(val itemId: String, var itemName: String, var createdDate: String)
const val UTC_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
fun main() {
    val list = mutableListOf<CartEntity>().apply {
        add(CartEntity(itemId = "", itemName = "", createdDate = "2020-07-28T14:28:52.877Z"))
        add(CartEntity(itemId = "", itemName = "", createdDate = "2020-09-28T14:28:52.877Z"))
        add(CartEntity(itemId = "", itemName = "", createdDate = "2020-08-28T14:28:52.877Z"))
        add(CartEntity(itemId = "", itemName = "", createdDate = "2020-04-28T14:28:52.877Z"))
    }
    Collections.sort(list, object : Comparator<CartEntity> {
        var f: DateFormat = SimpleDateFormat(UTC_FORMAT, Locale.ENGLISH)

        override fun compare(o1: CartEntity, o2: CartEntity): Int {
            return try {
                val firstitem = f.parse(o1.createdDate)
                val seconditem = f.parse(o2.createdDate)
                seconditem.compareTo(firstitem)
            } catch (e: ParseException) {
                throw IllegalArgumentException(e)
            }
        }
    })
    list
}

output:

CartEntity(itemId=, itemName=, createdDate=2020-09-28T14:28:52.877Z), 
CartEntity(itemId=, itemName=, createdDate=2020-08-28T14:28:52.877Z), 
CartEntity(itemId=, itemName=, createdDate=2020-07-28T14:28:52.877Z), 
CartEntity(itemId=, itemName=, createdDate=2020-04-28T14:28:52.877Z)

code from @Animesh Sahu also works!

val format: DateFormat = SimpleDateFormat(AppConstants.UTC_FORMAT, Locale.ENGLISH) list.sortByDescending { format.parse(it.createdDate) }