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

}
}

附件 ：