|NO.Z.00056|——————————|BigDataEnd|——|Hadoop&Scala.V04|——|Scala.v04|模式匹配和样例类|高阶函数|

一、高阶函数

### --- 高阶函数

~~~     高阶函数：接收一个或多个函数作为输入 或 输出一个函数。
~~~     函数的参数可以是变量，而函数又可以赋值给变量，
~~~     由于函数和变量地位一样，所以函数参数也可以是函数；
~~~     常用的高阶函数：map、reduce、flatMap、foreach、filter、count … … (接收函数作为参数)

### --- 编程示例

package yanqi.cn.part08

object HighFunction {
  def main(args: Array[String]): Unit = {
    //接收一个或多个函数作为输入的高阶函数
    val func = (n) => "*" * n
    (1 to 5).map(func(_)).foreach(println)

    //输出一个函数的高阶函数
    val URLBuilder = (ssl: Boolean, domainName: String) => {
      val schema = if (ssl) "https://" else "http://"
      //输出一个匿名函数
      (endpoint: String, query: String) => s"$schema$domainName/$endpoint?$query"
    }
    val domainName = "www.yanqi.com"

    def getURl = URLBuilder(true, domainName)

    val endpoint = "show"
    val query = "id=1"
    val url = getURl(endpoint, query)
    println(url)

  }
}

二、编程实现

### --- 编程代码

package yanqi.cn.part08

object HighFunction {
  def main(args: Array[String]): Unit = {
    //接收一个或多个函数作为输入的高阶函数
    val func = (n) => "*" * n
    (1 to 5).map(func(_)).foreach(println)

    //输出一个函数的高阶函数
    val URLBuilder = (ssl: Boolean, domainName: String) => {
      val schema = if (ssl) "https://" else "http://"
      //输出一个匿名函数
      (endpoint: String, query: String) => s"$schema$domainName/$endpoint?$query"
    }
    val domainName = "www.yanqi.com"

    def getURl = URLBuilder(true, domainName)

    val endpoint = "show"
    val query = "id=1"
    val url = getURl(endpoint, query)
    println(url)

  }
}

### --- 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=58677: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.part08.HighFunction
*
**
***
****
*****
https://www.yanqi.com/show?id=1

Process finished with exit code 0

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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

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