Kotlin: How to format a list of LocalDateTime to String?-CodePudding

I have succedded to format LocalDateTime to String but now how can I do the same for a list ?

The first function works but the second one doesn't work.

Here my class

class DateFormat {

    companion object {
    
        const val PATTERN = "dd-MM-yyyy HH:mm:ss"
    
        fun format(date: LocalDateTime): String {
            val formatter = DateTimeFormatter.ofPattern(PATTERN)
            return date.format(formatter)
        }
    
        fun formatList(date: List<LocalDateTime>): String {
            val formatter = DateTimeFormatter.ofPattern(PATTERN)
            return date.forEach {
                format(formatter)
            }
        }
    }
}

CodePudding user response：

to return a list of strings you could do this

fun formatList(date: List<LocalDateTime>): List<String> {
    val formatter = DateTimeFormatter.ofPattern(PATTERN)
    return date.map { it.format(formatter) }
}

or even shorter by referring to your other function like this:

fun formatList(date: List<LocalDateTime>): List<String> {
    return date.map { format(it)}
}

or even this to make it super short

fun formatList(date: List<LocalDateTime>) = date.map { format(it)}

Edit: realized you could even write this

fun formatList(date: List<LocalDateTime>) = date.map(::format)

CodePudding user response：

You would need to join your list elements to String. How a "good format" looks like is up to you, the example below will output your dates separated by a "|" - you can use any separator you want (note: this calls your first format function):

fun formatList(date: List<LocalDateTime>): String = date.joinToString(separator = "|") { format(it) }

EDIT: if you are on Android, note that the usage of DateTimeFormatter requires API level 26.

CodePudding user response：

Based on your second method implementation, you should return list of string instead of single result.

Also I have updated argument for first method to accept DateTimeFormatter, which will be useful while calling from second method.

class DateFormat {

    companion object {
    
        const val PATTERN = "dd-MM-yyyy HH:mm:ss"
    
        fun format(date: LocalDateTime, formatter: DateTimeFormatter): String {
            return date.format(formatter)
        }
    
        fun formatList(date: List<LocalDateTime>): List<String> {
            val listResult = listOf<String>()
            val formatter = DateTimeFormatter.ofPattern(PATTERN)
            date.forEach {
                listResult.add(format(formatter))
            }
            return listResult
        }
    }
}