|NO.Z.00050|——————————|BigDataEnd|——|Hadoop&Scala.V06|——|Scala.v06|模式匹配和样例类|样例类|

一、样例类

### --- 样例类

~~~     # case class样例类是Scala中特殊的类。当声明样例类时，以下事情会自动发生：
~~~     主构造函数接收的参数通常不需要显式使用var或val修饰，Scala会自动使用val修饰
~~~     自动为样例类定义了伴生对象，并提供apply方法，不用new关键字就能够构造出相应的对象
~~~     将生成toString、equals、hashCode和copy方法，除非显示的给出这些方法的定义
~~~     继承了Product和Serializable这两个特质，也就是说样例类可序列化和可应用Product的方法
~~~     # case class是多例的，后面要跟构造参数，case object是单例的。
~~~     # 此外，case class样例类中可以添加方法和字段，并且可用于模式匹配。

### --- 编程示例

class Amount
    //定义样例类Dollar，继承Amount父类
    case class Dollar(value: Double) extends Amount
    //定义样例类Currency，继承Amount父类
    case class Currency(value: Double, unit: String) extends Amount
    //定义样例对象Nothing，继承Amount父类
    case object Nothing extends Amount
    object CaseClassDemo {
    def main(args: Array[String]): Unit = {
    judgeIdentity(Dollar(10.0))
    judgeIdentity(Currency(20.2,"100"))
    judgeIdentity(Nothing)
}
//自定义方法，模式匹配判断amt类型
def judgeIdentity(amt: Amount): Unit = {
    amt match {
    case Dollar(value) => println(s"$value")
    case Currency(value, unit) => println(s"Oh noes,I got $unit")
    case Nothing => println("Oh,GOD!")
    }
    }
}

二、编程实现

### --- 编程代码

package yanqi.cn.part07

class Amount
//样例类中主构造器的参数默认用val修饰
//样例类中自动生成apply方法
case class Dollar(value: Double) extends Amount

case class Currency(value: Double, unit: String) extends Amount

case object Nothing extends Amount

object CaseClassDemo {
  def main(args: Array[String]): Unit = {
    judgeIdentity(Dollar(10.0))
    judgeIdentity(Currency(20.0, "100"))
    judgeIdentity(Nothing)
  }

  def judgeIdentity(amt: Amount): Unit = {
    amt match {
      case Dollar(value) => println(s"$value")
      case Currency(value, unit) => println(s"$value   $unit")
      case Nothing => println("nothing")
    }
  }
}

### --- 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=57843: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.CaseClassDemo
10.0
20.0   100
nothing

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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