Scala 学习笔记（8）

2019独角兽企业重金招聘Python工程师标准>>>

一、trait

trait Logger {
  def log(msg: String)
}

class ConsoleLogger extends Logger with Serializable{
  def log(msg: String) {println(msg)}
}

注意，没有implements，用extends就好了，另外，这里其实也是override，但是不需要写上。log在Logger当中是抽象的，如果要实现多个trait，用with连上就行了。另外，跟java一样，一个父类+若干个Interface

二、有具体实现的特质

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

class Account(val name: String, val password: String) extends Logger {
  def check() = {log("Account = " + name + " and password = " + password); name == "bajie" && password == "change" }
}

object Account {
  def main(args: Array[String]) {
    val acc = new Account("bajie", "change")
    acc.check
  }
}

前一节当中，对trait的使用，类似于java的interface。那么本节当中，它该怎么理解？

三、带有trait的对象

trait Logger {
  def log(msg: String) {}
}

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

class Account(val name: String, val password: String) extends Logger {
  def check() = {log("Account = " + name + " and password = " + password); name == "bajie" && password == "change" }
}

object Account {
  def main(args: Array[String]) {
    val acc = new Account("bajie", "change")
    acc.check
    
    val acc1 = new Account("bajie", "change") with ConsoleLogger
    acc1.check
  }
}

又做了一些修改， Logger.log有一个空实现， ConsoleLogger.log干了活了， Account 混合了 Logger ，所以 acc.check ，并不做输出的工作，而 val acc1 = new Account("bajie", "change") with ConsoleLogger ，acc1.check有输出了。

好吧，目前我还想不清楚这样的一种设计，具体应该用来完成什么样的工作，但是它一定是有用的，尽量记住它吧。

四、特质的叠加（屌爆了）

trait Logger {
  def getLog: String = "I am the root; "
}

trait ConsoleLogger extends Logger {
  override def getLog = super.getLog + "Something happend "
}

trait TimeLogger extends Logger{
  override def getLog = super.getLog + "at " + new Date() + " "
}

class Account(val name: String, val password: String) extends Logger {
  def check() = {println(getLog); name == "bajie" && password == "change" }
}

object Account {
  def main(args: Array[String]) {   
    val acc1 = new Account("bajie", "change") with TimeLogger with ConsoleLogger
    acc1.check
    
    val acc2 = new Account("bajie", "change") with ConsoleLogger with TimeLogger
    acc2.check
  }
}

最后是输出

I am the root;
I am the root; at Fri Aug 12 01:32:24 PDT 2016 Something happend
I am the root; Something happend at Fri Aug 12 01:32:24 PDT 2016

体会一下吧，说不清楚了！

五、interface + abstract class

trait Logger {
  def log(message: String)
  def info(message: String) {println(message)}
}

class Account extends Logger {
  var accName = "bajie"
  var accPass = "change"
  def check() = {info("a user login "); accName == "bajie" && accPass == "change"}

  def log(message: String) { println(message) }
}

在这里Logger，既是一个interface，又是一个abstract class。Account可以直接使用info方法，又必须自己实现log方法。

六、具体属性和抽象属性

trait Logger {
  def log(message: String)
  def info(message: String) {println(message)}
 
  val logLevel: Int
  val maxlength = 20
}

class Account extends Logger {
  var accName = "bajie"
  var accPass = "change"
  def check() = {info("a user login "); accName == "bajie" && accPass == "change"}

  def log(message: String) { println(message) }
 
  val logLevel = 3
}

和前面一节类似，属性也有具体和抽象之分，具体字段可以再Account当中直接使用，抽象字段必须具体化。

转载于:https://my.oschina.net/dongtianxi/blog/731894