|NO.Z.00072|——————————|BigDataEnd|——|Hadoop&Scala.V04|——|Scala.v04|隐式机制|隐式参数和隐式值|

一、隐式参数和隐式值

### --- 隐式参数和隐式值

~~~     在函数定义的时候，支持在最后一组参数中使用 implicit ，表明这是一组隐式参数。
~~~     在调用该函数的时候，可以不用传递隐式参数，
~~~     而编译器会自动寻找一个implicit 标记过的合适的值作为参数。

### --- Scala编译器会在两个范围内查找：

~~~     当前作用域内可见的val或var定义隐式变量
~~~     隐式参数类型的伴生对象内隐式值

### --- 编程示例

object Doubly {
    //在print函数中定义一个隐式参数fmt
    def print(num: Double)(implicit fmt: String): Unit = {
        println(fmt format (num))
    }
    def main(args: Array[String]): Unit = {
        //此时调用print函数需要为第二个隐式参数赋值
        print(3.12)("%.1f")
        //定义一个隐式变量
        implicit val printFmt="%.3f"
        //当调用print函数时没有给第二个隐式参数赋值，
        //那么Scala会在当前作用域内寻找可见的val或var定义的隐式变量，一旦找到就会应用
        print(3.12)
}
}

二、编程实现

### --- 编程代码

package yanqi.cn.part10

object DoublyDemo {
  def print(num:Double)(implicit fmt:String): Unit ={
    println(fmt format(num))
  }

  def main(args: Array[String]): Unit = {
    print(3.245)("%.1f")

    //定义一个隐式变量
    implicit val printFmt="%.3f"
    print(3.24)
  }
}

### --- 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=61336: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.part10.DoublyDemo
3.2
3.240

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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