Scala学习之延迟绑定

package com.swust.example
 
object TraitDemo2 extends App{
 
   //抽象类
     abstract class Writer {
        def writeMessage(message: String)
     }
     /**
      * 继承这个抽象类，并且用super调用了这个抽象方法
      * scala要求将方法声明为abstract override
      * override告诉scala要为基类的一个已知方法提供一个实现
      * abstract表示这个方法实际最后的终极实现要由混入这个trait的类提供
      */
     trait UpperCaseWriter extends Writer{
        abstract override def writeMessage(message: String)={
           super.writeMessage(message.toUpperCase)
        }
     }
     /**
      * 为了调用super.writeMessage，scala做了两件事情
      * 1、对这个调用进行了延迟绑定
      * 2、要求混入这些trait的类提供该方法的实现
      */
     trait WordFilterWriter extends Writer{
        abstract override def writeMessage(message: String)={
           super.writeMessage(message.replace("stupid","s-----"))
        }
     }
     class StringWriterDelegate extends Writer{
        val writer = new java.io.StringWriter
        //实现抽象类的方法，不用override
        def writeMessage(message: String) = writer.write(message)
        override def toString(): String = writer.toString
     }
     //创建实例时混入trait
     val first = new StringWriterDelegate with UpperCaseWriter with WordFilterWriter
     val last = new StringWriterDelegate with WordFilterWriter with UpperCaseWriter
     first.writeMessage("there is no sin except stupidity")
     last.writeMessage("there is no sin except stupidity")
     println(first)
     println(last)
      
}