为什么这段代码同时打印"initialization1“和"initialization2"，而只打印一个doAction？

Question

trait Action {
  def doAction
}

trait TBeforeAfter extends Action {
  abstract override def doAction: Unit = {
    println("Initialization")
    super.doAction 
    println("Destoryed")
  }
}

trait TBeforeAfter2 extends Action {
  abstract override def doAction: Unit = {
    println("Initialization2")
    super.doAction 
    println("Destoryed2")
  }
}

class Work extends Action {
  override def doAction = println("doAction")
}

object TraitLearning extends App {
  val work = new Work with TBeforeAfter with TBeforeAfter2
  work.doAction
}

成果产出：

Initialization2
Initialization
doAction
Destoryed
Destoryed2

有人能告诉我为什么只叫一次doAction而叫两次吗？

Answer 1

这两个特征，Work和他们的doAction方法都被称为。调用链是这样执行的：

1. work.doAction ->调用TBeforeAfter2.doAction，因为它是实例化图中的最后一次混合。
2. TBeforeAfter2.doAction打印"Initialization2"，并调用super.doAction，这是TBeforeAfter.doAction，是对象图中的下一个混音。
3. TBeforeAfter.doAction打印“初始化”，并调用它的super，即Work。
4. Work.doAction打印"doAction"，并返回
5. TBeforeAfter.doAction打印“销毁”并返回到TBeforeAfter2
6. TBeforeAfter2.doAction打印"Destroyed2“并返回，并结束调用链。