快学Scala 第二十课 （trait的构造顺序）

trait的构造顺序：

1. 首先调用超类构造器
2. 特质构造器在超类构造器之后，类构造器之前执行
3. 特质从左向右被构造
4. 每个特质当中，父特质先被构造
5. 如果多个特质共有一个父特质，而那个父特质已经被构造，则不会被再次构造
6. 所有特质构造完毕，子类被构造

class Account {
  println("Account constructor")
}

trait Logged {
  println("Logged constructor")
  def log(msg: String){ println("Logged")}
}

trait LongLogger extends Logged{
  println("LongLogger constructor")
   override def log(msg: String){
   println("LongLogger")  
     super.log(msg)
  }
  
}

trait ShortLogger extends Logged{
    println("ShortLogger constructor")  
   override def log(msg: String){
   println("ShortLogger")  
     super.log(msg)
  }
  
}

trait ConsoleLogger extends Logged {
  println("ConsoleLogger constructor")
  
 override def log(msg: String){
   println("ConsoleLogger")
    super.log(msg)
  }
  
}

trait DetailedLogger{
  println("DetailedLogger constructor")
   def log2(msg: String){
    println("DetailedLogger")
  }
  
}

class SavingsAccount extends Account with LongLogger with ShortLogger with ConsoleLogger {
  println("SavingsAccount constructor")
  log("funds")
  
}

new SavingsAccount() with DetailedLogger

运行结果：

Account constructor
Logged constructor
LongLogger constructor
ShortLogger constructor
ConsoleLogger constructor
SavingsAccount constructor
ConsoleLogger
ShortLogger
LongLogger
Logged
DetailedLogger constructor