Scala.List和Java.util.List之間的互操作

Question

我是Scala新手。我正在使用谷歌番石榴庫Collections2.permutations()方法作爲輸入java.util.Collection collection

我有下面的代碼，改編自我寫的相應的Java程序。

import java.util 

import com.google.common.collect.Collections2 
import collection.JavaConversions._ 

class OptimalTSP { 

    def distance(point1: Point, point2: Point): Double = { 
     Math.sqrt(Math.pow(point2.y - point1.y, 2) + Math.pow(point2.x - point1.x, 2)) 
    } 

    def findCheapestPermutation(points: java.util.List[Point]): java.util.List[Point] = { 
     var cost: Double = Double.MaxValue 
     var minCostPermutation: java.util.List[Point] = null 
     val permutations: util.Collection[java.util.List[Point]] = Collections2.permutations(points) 
     import scala.collection.JavaConversions._ 
     for (permutation <- permutations) { 
     val permutationCost: Double = findCost(permutation) 
     if (permutationCost <= cost) { 
      cost = permutationCost 
      minCostPermutation = permutation 
     } 
     } 
     println("Cheapest distance: " + cost) 
     minCostPermutation 
    } 
} 

上述工作正常，但明確需要完整軟件包名稱java.util.List。有沒有一種更習慣的scala方法來做到這一點，即將scala List轉換成預計Java Collection的方法？

Answer 1

更地道，你可以嘗試使用permutations和minBy：

points.permutations.minBy(permutation => findCost(permutation)) 
points.permutations.minBy(findCost) //equivalent 

Answer 2

正如鮑里斯指出permutation的方法scala List可以直接使用，如下圖所示。

class OptimalTSP { 

    def distance(point1: Point, point2: Point): Double = { 
     Math.sqrt(Math.pow(point2.y - point1.y, 2) + Math.pow(point2.x - point1.x, 2)) 
    } 

    def findCheapestPermutation(points: List[Point]): List[Point] = { 
    var cost: Double = Double.MaxValue 
    var minCostPermutation: List[Point] = null 
    for (permutation <- points.permutations) { 
     val permutationCost: Double = findCost(permutation) 
     if (permutationCost <= cost) { 
     cost = permutationCost 
     minCostPermutation = permutation 
     } 
    } 
    println("Cheapest distance: " + cost) 
    minCostPermutation 
    } 
}