Kotlin使用Haversine公式根據物件的坐標（緯度和經度）對物件串列進行排序

我想根據他們的緯度和經度對串列進行排序......這是我的代碼：

import java.util.*
import com.google.gson.GsonBuilder
import java.io.File
import java.io.InputStream
import java.util.Comparator

data class Property(val Pcode: Int, val Locality: String, val State: String, val Comments: String, val Category: String, val Longitude: Double, val Latitude: Double)


class SortPlaces(currentLatitude: Double, currentLongitude: Double) : Comparator<Property> {
    var currentLat: Double
    var currentLng: Double
    override fun compare(property1: Property, property2: Property): Int {
        val lat1: Double = property1.Latitude
        val lon1: Double = property1.Longitude
        val lat2: Double = property2.Latitude
        val lon2: Double = property2.Longitude
        val distanceToPlace1 = distance(currentLat, currentLng, lat1, lon1)
        val distanceToPlace2 = distance(currentLat, currentLng, lat2, lon2)
        return (distanceToPlace1 - distanceToPlace2).toInt()
    }

    fun distance(fromLat: Double, fromLon: Double, toLat: Double, toLon: Double): Double {
        val radius = 6378137.0 // approximate Earth radius, *in meters*
        val deltaLat = toLat - fromLat
        val deltaLon = toLon - fromLon
        val angle = 2 * Math.asin(
            Math.sqrt(
                Math.pow(Math.sin(deltaLat / 2), 2.0)  
                        Math.cos(fromLat) * Math.cos(toLat) *
                        Math.pow(Math.sin(deltaLon / 2), 2.0)
            )
        )
        return radius * angle
    }

    init {
        currentLat = currentLatitude
        currentLng = currentLongitude
    }
}

fun main(args: Array<String>) {
    val command = Scanner(System.`in`)
    val running = true

    while (running) {

        val inputStream: InputStream = File("./src/main/kotlin/suburbs.json").inputStream()
        val inputString = inputStream.bufferedReader().use { it.readText() }
        val gson = GsonBuilder().create()
        val packagesArray = gson.fromJson(inputString , Array<Property>::class.java).toList()

        println("Please enter a suburb name: ")
        val suburbName = command.nextLine()

        println("Please enter the postcode: ")
        val postcode = command.nextLine()

        val userProperty: Property? = packagesArray.find{ it.Locality.toLowerCase().equals(suburbName.toLowerCase()) && it.Pcode == postcode.toInt()}

        //sort the list, give the Comparator the current location
        Collections.sort(packagesArray, new SortPlaces(userProperty.Latitude, userProperty.Longitude));


    }
    command.close()
}

我收到錯誤：公共開放樂趣的引數太多 <T : Comparable<T!>!> sort(list: (Mutable)List<T!>!): Unit defined in java.util.Collections at my sort{} 函式我的 userProperty 必須是 Property？因為 find{} 方法回傳屬性？那么 Collections.sort() 不能排序屬性？鍵入因為 SortPLaces 只接受 Comparator 而不是 Comparator<Property?> 我該怎么辦？

uj5u.com熱心網友回復：

您的代碼中有多個錯誤。要在 Kotlin 中創建一個新物件，您不必new像在 Java 中那樣撰寫單詞。此外，正如您所注意到的，它find回傳一個可為空的型別 - Property?。使用時需要檢查空值userProperty。Property畢竟，不一定能找到符合您想要的標準的A。

if (userProperty != null) {
    Collections.sort(packagesArray, SortPlaces(userProperty.Latitude, userProperty.Longitude))
} else {
    // no property is found! Think about what you should do in such a case
}

由于您正在對串列進行排序，因此在toList反序列化 JSON 時不應創建不可變串列，而應使用MutableList：

val packagesArray = gson.fromJson(inputString, Array<Property>::class.java).toMutableList()

此外，您似乎使用了很多 Java API。在 Kotlin 中，您使用的許多 Java API 都有更慣用的 Kotlin 對應物。要對串列進行排序，您根本不需要SortPlaces該類。只需sortBy在陣列上使用，然后distance在 lambda 中呼叫您的函式。

data class Property(
    val pcode: Int,
    val locality: String,
    val state: String,
    val comments: String,
    val category: String,
    val longitude: Double,
    val latitude: Double,
    )


fun distance(fromLat: Double, fromLon: Double, toLat: Double, toLon: Double): Double {
    val radius = 6378137.0 // approximate Earth radius, *in meters*
    val deltaLat = toLat - fromLat
    val deltaLon = toLon - fromLon
    val angle = 2 * asin(
        sqrt(
            sin(deltaLat / 2).pow(2.0)  
                    cos(fromLat) * cos(toLat) *
                    sin(deltaLon / 2).pow(2.0)
        )
    )
    return radius * angle
}

fun main(args: Array<String>) {
    val running = true

    while (running) {
        val inputStream = File("./src/main/kotlin/suburbs.json").inputStream()
        val inputString = inputStream.bufferedReader().use { it.readText() }
        val gson = GsonBuilder().create()
        val packagesArray = gson.fromJson(inputString , Array<Property>::class.java).toMutableList()

        println("Please enter a suburb name: ")
        val suburbName = readLine()

        println("Please enter the postcode: ")
        val postcode = readLine()

        val userProperty = packagesArray.find {
            it.locality.lowercase() == suburbName?.lowercase() && it.pcode == postcode?.toInt()
        }

        //sort the list, give the Comparator the current location
        if (userProperty != null) {
            packagesArray.sortBy {
                distance(userProperty.latitude, userProperty.longitude, it.latitude, it.longitude)
            }
        } else {
            // did not find such a property!
        }

    }
}

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