|NO.Z.00048|——————————|BigDataEnd|——|Hadoop&Scala.V04|——|Scala.v04|模式匹配和样例类|匹配类型|

一、匹配类型

### --- 匹配类型

~~~     Scala的模式匹配还有一个强大的功能，它可以直接匹配类型，而不是值。
~~~     这一点是Java的switch case做不到的。
~~~     匹配类型的语法：case 变量 : 类型 => 代码，而不是匹配值的“case 值 => 代码”这种语法。

### --- 代码示例

def main(args: Array[String]): Unit = {
    val a = 3
    val obj = if(a == 1) 1
else if(a == 2) "2"
else if(a == 3) BigInt(3)
else if(a == 4) Map("aa" -> 1)
else if(a == 5) Map(1 -> "aa")
else if(a == 6) Array(1, 2, 3)
else if(a == 7) Array("aa", 1)
else if(a == 8) Array("aa")
val r1 = obj match {
    case x: Int => x
    case s: String => s.toInt
    // case BigInt => -1 //不能这么匹配
    case _: BigInt => Int.MaxValue
    case m: Map[String, Int] => "Map[String, Int]类型的Map集合"
    case m: Map[_, _] => "Map集合"
    case a: Array[Int] => "It's an Array[Int]"
    case a: Array[String] => "It's an Array[String]"
    case a: Array[_] => "It's an array of something other than Int"
    case _ => 0
}
println(r1 + ", " + r1.getClass.getName)
}

二、编程实现

### --- 编程代码

package yanqi.cn.part07

import scala.util.Random

object MatchDemo {
  def main(args: Array[String]): Unit = {
    //对字符进行模式匹配
    val character = '*'
    character match {
      case '+' => println("加号")
      case '-' => println("减号")
      case '*' => println("乘号")
      case '/' => println("除号")
      case _ => println("不是运算符！")
    }

    //对字符串进行模式匹配
    val content = Array("hadoop", "spark", "flink")
    val project = content(Random.nextInt(content.length))

    project match {
      case "hadoop" => println("大数据计算框架")
      case "spark" => println("大数据内存框架")
      case "flink" => println("大数据实时框架")
      case _ => println("不送，慢走~~")
    }

    //守卫式匹配，添加if判断
    val char = '/'
    val num = char match {
      case '+' => 1
      case '-' => 2
      case _ if char.equals('*') => 3
      case _ => 4
    }
    println(num)

    typeMatch(Array(1,2))
  }

  //匹配类型，语法：case 变量:类型 => 代码
  def typeMatch(x: Any) = {
    x match {
      case x: String => println("这是一个字符串类型")
      case x: Int => println("是一个整型")
      case x: Boolean if (x == false) => println("是一个false的布尔类型")
      case x: Array[Int] => println("是一个整型数组")
      case _ => println("不知是啥类型！")
    }
  }
}

### --- 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=57628: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.part07.MatchDemo
乘号
大数据实时框架
4
是一个整型数组

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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