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)

 }