|NO.Z.00041|——————————|BigDataEnd|——|Hadoop&Scala.V03|——|Scala.v03|特质|特质构造顺序|

一、特质构造顺序

### --- 特质构造顺序

~~~     在Scala中，trait特质也是有构造器的，也就是trait中的不包含在任何方法中的代码。

### --- 构造器以如下顺序执行：

~~~     执行父类的构造器；
~~~     执行trait的构造器，多个trait从左到右依次执行；
~~~     构造trait时会先构造父trait，如果多个trait继承同一个父trait，则父trait只会构造一次；
~~~     所有trait构造完毕之后，子类的构造器才执行

### --- 编程示例

class Person2 { println("Person's constructor!") }
trait Logger { println("Logger's constructor!") }
trait MyLogger extends Logger { println("MyLogger's constructor!") }
trait TimeLogger extends Logger { println("TimeLogger's constructor!") }
//类既继承了类又继承了特质，要先写父类
class Student2 extends Person2 with MyLogger with TimeLogger {
    println("Student's constructor!")
}

### --- 上面代码的输出结果：

Person's constructor!
Logger's constructor!
MyLogger's constructor!
TimeLogger's constructor!
Student's constructor!

二、编程实现

### --- 编程代码

package yanqi.cn.part06

class Person2 {
  println("Person's Constructor!")
}

trait Logger {
  println("Logger's Constructor!")
}

trait MyLogger extends Logger {
  println("MyLogger's Constructor!")
}

trait TimeLogger extends Logger {
  println("TimeLogger's Constructor!")
}

//如果一个类既继承了父类，也继承特质，那么要先写父类，再写特质
//extends 父类  with 特质1 with 特质2.....
class Student2 extends Person2 with MyLogger with TimeLogger {
  println("Student's Constructor!")
}

object TraitDemoThree {
  def main(args: Array[String]): Unit = {
    val stu = new Student2
  }
}

### --- 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=57055: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.TraitDemoThree
Person's Constructor!
Logger's Constructor!
MyLogger's Constructor!
TimeLogger's Constructor!
Student's Constructor!

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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