|NO.Z.00035|——————————|BigDataEnd|——|Hadoop&Scala.V02|——|Scala.v02|继承|构造器执行顺序|

一、构造器执行顺序

### --- 构造器执行顺序

~~~     Scala在继承的时候构造器的执行顺序：首先执行父类的主构造器，其次执行子类自身的主构造器。
~~~     类有一个主构造器和任意数量的辅助构造器，
~~~     而每个辅助构造器都必须以对先前定义的辅助构造器或主构造器的调用开始。
~~~     子类的辅助构造器最终都会调用主构造器。只有主构造器可以调用父类的构造器。

### --- 编程示例

// Person类
class Person(name:String,age:Int){
    println("这是父类Person")
}

//Student继承Person类
class Student(name:String,age:Int,studentNo:String) extends Person(name,age){
    println("这是子类Student")
}

object Demo{
    def main(args: Array[String]): Unit = {
        //下面的语句执行时会打印下列内容:
        //这是父类Person
        //这是子类Student
        //也就是说，构造Student对象之前，首先会调用Person的主构造器
        val student=new Student("john",18,"1024")
}
}

二、编程实现

### --- 编程代码

package yanqi.cn.part05

class Person(name: String, age: Int){
  println("这是父类Person！")
}

class Student(name: String, age: Int, var stuNo: String) extends Person(name, age){
  println("这是子类Student！")
}

object ExtendsDemo {
  def main(args: Array[String]): Unit = {
    val student = new Student("jacky", 30, "1001")
//    student.stuNo="1002"
//    println(student.stuNo)
  }
}

### --- 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=56444: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.part05.ExtendsDemo
这是父类Person！
这是子类Student！

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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