一、Ordered和Ordering
### --- Ordered和Ordering
~~~ 在Java中对象的比较有两个接口，分别是Comparable和Comparator。它们之间的区别在于：
~~~ 实现Comparable接口的类，重写compareTo()方法后，其对象自身就具有了可比较性；
~~~ 实现Comparator接口的类，重写了compare()方法后，
~~~ 则提供一个第三方比较器，用于比较两个对象。
~~~ 在Scala中也引入了以上两种比较方法(Scala.math包下):
~~~ Ordered特质混入Java的Comparable接口，
~~~ 它定义了相同类型间的比较方式，但这种内部比较方式是单一的；
trait Ordered[A] extends Any with java.lang.Comparable[A]{......}
~~~ # Ordering特质混入Comparator接口，
~~~ 它是提供第三方比较器，可以自定义多种比较方式，在实际开发中也是使用比较多的，灵活解耦合。
trait Ordering[T] extends Comparator[T] with PartialOrdering[T] with Serializable {......}
### --- 使用Ordered特质进行排序操作
case class Project(tag:String, score:Int) extends Ordered[Project] {
def compare(pro:Project ) = tag.compareTo(pro.tag)
}
object OrderedDemo {
def main(args: Array[String]): Unit = {
val list = List(Project("hadoop",60), Project("flink",90),
Project("hive",70),Project("spark",80))
println(list.sorted)
}
}
~~~ # 使用Ordering特质进行排序操作
object OrderingDemo {
def main(args: Array[String]): Unit = {
val pairs = Array(("a", 7, 2), ("c", 9, 1), ("b", 8, 3))
// Ordering.by[(Int,Int,Double),Int](_._2)表示从Tuple3转到Int型
// 并按此Tuple3中第二个元素进行排序
Sorting.quickSort(pairs)(Ordering.by[(String, Int, Int), Int](_._2))
println(pairs.toBuffer)
}
}
二、编程实现
### --- 编程代码
package yanqi.cn.part06
import scala.util.Sorting
case class Project(tag: String, score: Int) extends Ordered[Project] {
override def compare(that: Project): Int = {
tag.compareTo(that.tag)
}
}
object OrderDemo {
def main(args: Array[String]): Unit = {
val list = List(Project("hadoop", 40), Project("flink", 90), Project("spark", 80), Project("hive", 60))
println(list.sorted)
val pairs = Array(("a", 7, 2), ("b", 9, 1), ("c", 8, 3))
//Ordering.by[(String,Int,Int),Int](_._2)表示从Tuple3转到Int型，根据Tuple3中的第二个元素进行排序
Sorting.quickSort(pairs)(Ordering.by[(String,Int,Int),Int](_._2))
println(pairs.toBuffer)
}
}
### --- 编译打印
D:\JAVA\jdk1.8.0_231\bin\java.exe "-javaagent:D:\IntelliJIDEA\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=57219:D:\IntelliJIDEA\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath D:\JAVA\jdk1.8.0_231\jre\lib\charsets.jar;D:\JAVA\jdk1.8.0_231\jre\lib\deploy.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\access-bridge-64.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\cldrdata.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\dnsns.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\jaccess.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\jfxrt.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\localedata.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\nashorn.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunec.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunjce_provider.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunmscapi.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunpkcs11.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\zipfs.jar;D:\JAVA\jdk1.8.0_231\jre\lib\javaws.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jce.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jfr.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jfxswt.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jsse.jar;D:\JAVA\jdk1.8.0_231\jre\lib\management-agent.jar;D:\JAVA\jdk1.8.0_231\jre\lib\plugin.jar;D:\JAVA\jdk1.8.0_231\jre\lib\resources.jar;D:\JAVA\jdk1.8.0_231\jre\lib\rt.jar;E:\NO.Z.10000——javaproject\NO.Z.00002.Hadoop\ScalaPro\out\production\ScalaPro;D:\JAVA\scala-2.12.2\lib\scala-library.jar;D:\JAVA\scala-2.12.2\lib\scala-reflect.jar yanqi.cn.part06.OrderDemo
List(Project(flink,90), Project(hadoop,40), Project(hive,60), Project(spark,80))
ArrayBuffer((a,7,2), (c,8,3), (b,9,1))
Process finished with exit code 0
Walter Savage Landor:strove with none,for none was worth my strife.Nature I loved and, next to Nature, Art:I warm'd both hands before the fire of life.It sinks, and I am ready to depart
——W.S.Landor
