Sort List<T> based on String DateTime - kotlin

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) }