Scala提供两个特质（trait）Ordered与Ordering用于比较。其中，Ordered混入（mix）Java的Comparable接口，而Ordering则混入Comparator接口。众所周知，在Java中
Ordered与Ordering的区别与之相类似：
Ordered特质更像是rich版的Comparable接口，除了compare方法外，更丰富了比较操作（<, >, <=, >=）：
trait Ordered[T] extends Comparable[T] {
def compare(that: A): Int
def < (that: A): Boolean = (this compare that) < 0
def > (that: A): Boolean = (this compare that) > 0
def <= (that: A): Boolean = (this compare that) <= 0
def >= (that: A): Boolean = (this compare that) >= 0
def compareTo(that: A): Int = compare(that)
}
Ordering，内置函数Ordering.by与Ordering.on进行自定义排序：
import scala.util.Sorting
val pairs = Array(("a", 5, 2), ("c", 3, 1), ("b", 1, 3))
// sort by 2nd element
Sorting.quickSort(pairs)(Ordering.by[(String, Int, Int), Int](_._2))
// sort by the 3rd element, then 1st
Sorting.quickSort(pairs)(Ordering[(Int, String)].on(x => (x._3, x._1)))
参考文献：
【1】Scala比较器：Ordered与Ordering - Jason的专栏 - CSDN博客
原文：https://www.cnblogs.com/nxf-rabbit75/p/11829001.html