空指针异常

空指针异常

目标：实现日志类，可以吧一些文本相信写入指定的文件中

eg:

object class18 {
  trait Log {
    //文件名，抽象属性
    var fileName:String

    println(s"${fileName}")
    //具体属性
    //lazy 懒加载，懒
    lazy val fileWriter:FileWriter = new FileWriter(fileName)

    def writeLog (msg:String):Unit = {
      fileWriter.write(msg)
      fileWriter.close()
    }
  }
  //先执行父类构造器，所以报错
  class TextLog extends Log {
    var fileName:String = "text.log"
  }
  def main(args: Array[String]): Unit = {
    val textLog = new TextLog()
    textLog.writeLog("2025-11-19:下午，天气晴朗")
  }
}