scala特质

1.scala中不支持多继承类，但是可以多继承特质

2.当做接口使用的特质

//特质可以同时拥有抽象方法和具体方法
trait Logger {
  def log(msg: String) //抽象方法  无需使用abstract关键字
}

class ConsoleLogger extends Logger with Serializable with Cloneable { //多个特质使用with连接
  override def log(msg: String): Unit = {
    println(msg)
  }
}

3.带有具体实现的特质

trait ConsoleLogger {
  def log(msg: String) {
    println(msg)
  }
}

class Account extends ConsoleLogger {
  //ConsoleLogger的功能混入Account类中
}

4.带有特质的对象

trait ConsoleLogger {
  def log(msg: String) {
    println(msg)
  }
}

class Account {

}

object Test extends App {
  val account = new Account with ConsoleLogger
  account.log("....")
}

5.叠加在一起的特质

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

//给日志消息添加时间戳
trait TimestampLogger extends Logged {
  override  def log(msg: String): Unit = super.log(new java.util.Date() + " " + msg)
}

//截断冗长的日志消息
trait ShortLogger extends Logged {
  val maxLength = 15

  override def log(msg: String): Unit = {
    if (msg.length < maxLength) {
      super.log(msg)
    } else {
      super.log(msg.substring(0, msg.length - 3))
    }
  }
}

class Account {

}

class SavingsAccount extends Account {

}

object Test extends App {
  val acct1 = new SavingsAccount with TimestampLogger with ShortLogger //从右向左执行
  acct1.log("abcdefg")
  
}

6.特质中重写抽象方法

trait Logged {
  def log(msg: String) //抽象方法
}


trait TimestampLogger extends Logged {
  override def log(msg: String): Unit = super.log(new java.util.Date() + " " + msg)
}

class Account {}

object Test extends App {
  val account = new Account with TimestampLogger
  account.log("a")

  Error:(7, 47) method log in trait Logged is accessed from super. It may not be abstract unless it is overridden by a member declared `abstract' and `override'
  override def log(msg: String): Unit = super.log(new java.util.Date() + " " + msg)
}

trait Logged {
  def log(msg: String) //抽象方法
}


trait TimestampLogger extends Logged {
  abstract override def log(msg: String): Unit = super.log(new java.util.Date() + " " + msg)
}

class Account {}

object Test extends App {


}

7.当做富接口使用的特质

trait Logged {
  def log(msg: String)

  def info(msg: String) {
    log("info: " + msg)
  }

  def warn(msg: String) {
    log("warn: " + msg)
  }

  def severs(msg: String) {
    log("severs: " + msg)
  }
}

class Account extends Logged {
  override def log(msg: String): Unit = {
    println(msg)
  }
}

object Test extends App {


}

10.特质构造顺序

/*
特质构造顺序
1.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
3.特质由左到右被构造
4.每个特质中父特质先被构造
5.多个特质公用一个父特质，父特质只会被构造一次
6.所有特质构造完成，子类被构造
 */
trait Logger {

}

trait FileLogger extends Logger {}

trait ShortLogger extends Logger {}

class Account {}

class SavingsAccount extends Account with FileLogger with ShortLogger {}

/*
1.Account(超类)
2.Logger(第一个特质父特质)
3.FileLogger(第一个特质)
4.ShortLogger(第二个特质)  父特质已经被构造
5.SavingsAccount(类)

 */