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)

 }