Scala：基于trait的多重继承构造器的执行顺序、基于trait的AOP实践

多重继承

package kmust.hjr.learningScala15/** * Created by Administrator on 2015/7/20. */class  Human{  println("Human")}trait TTeacher extends Human{  println("TTeacher")    def teach}trait PianoPlayer extends Human{  println("PianoPlayer")    def playPiano={println("I'm playing piano.")}}class PianoTeacher extends Human with TTeacher with PianoPlayer{  override def teach={println("I'm training students. ")}}

实例一

object UseTrait {  def main(args:Array[String]): Unit ={    val t1=new PianoTeacher    t1.playPiano    t1.teach  }}

**说明（1）：**class PianoTeacher extends Human with TTeacher with PianoPlayer{...}的构造顺序为：**从左向右**。即：先构造Human ，在构造TTeacher ，之后构造PianoPlayer。

说明（2）：在构造TTeacher的时候，发现它的父类Human已经被构造，就不会再重复构造（这是Scala特有的）,同理，构造TTeacher的时候，发现它的父类Human已经被构造，则不必重复构造。 

实例二

object UseTrait {  def main(args:Array[String]): Unit ={    val t1=new PianoTeacher    t1.playPiano    t1.teach    val t2= new Human with TTeacher with PianoPlayer{      def teach={println("I'm teaching students.")}    }    t2.playPiano    t2.teach  }}

AOP

package kmust.hjr.learningScala15/** * Created by Administrator on 2015/7/20. *//*AOP*/trait Action{  def doAction}trait TBeforeAfter extends Action{  abstract override def doAction: Unit ={    println("Initialization")    super.doAction    println("Destroyed")  }}class Work extends Action{  override def doAction=println("Working...")}

object UseTrait {  def main(args:Array[String]): Unit ={    val work=new Work with TBeforeAfter    work.doAction  }}

完整代码

package kmust.hjr.learningScala15/** * Created by Administrator on 2015/7/20. */class  Human{  println("Human")}trait TTeacher extends Human{  println("TTeacher")    def teach}trait PianoPlayer extends Human{  println("PianoPlayer")    def playPiano={println("I'm playing piano.")}}class PianoTeacher extends Human with TTeacher with PianoPlayer{  override def teach={println("I'm training students. ")}}/*AOP*/trait Action{  def doAction}trait TBeforeAfter extends Action{  abstract override def doAction: Unit ={    println("Initialization")    super.doAction    println("Destroyed")  }}class Work extends Action{  override def doAction=println("Working...")}object UseTrait {  def main(args:Array[String]): Unit ={  /*  val t1=new PianoTeacher    t1.playPiano    t1.teach    val t2= new Human with TTeacher with PianoPlayer{      def teach={println("I'm teaching students.")}    }    t2.playPiano    t2.teach*/    val work=new Work with TBeforeAfter    work.doAction  }}

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