Scala 多继承问题
2024-08-31 08:55:53
多继承问题：
object LoadIssueDemo extends App {
import java.io.PrintWriter
trait Logger {
def log(msg: String): Unit
}
trait FileLogger extends Logger {
val fileName: String
val fileOutput = new PrintWriter(fileName: String)
fileOutput.println("#")
def log(msg: String): Unit = {
fileOutput.print(msg)
fileOutput.flush()
}
}
class Person
class Student(var name: String) extends Person with FileLogger {
override val fileName: String = "file.log"
}
new Student("Win").log("trait demo")
}
运行结果：
原因：fileName还未初始化，就被方法调用。
解决方法：
1. 提前定义 （代码不够优雅）
object PreDefineDemo extends App{
import java.io.PrintWriter
trait Logger{
def log(msg: String): Unit
}
trait FileLogger extends Logger {
val fileName: String
val fileOutput = new PrintWriter(fileName: String)
fileOutput.println("#")
def log(msg: String): Unit ={
fileOutput.print(msg)
fileOutput.flush()
}
}
class Person
class Student(var name: String) extends Person with FileLogger{
override val fileName: String = "file.log"
}
new { override val fileName: String = "file.log"} with Student("Win").log("trait demo")
}
2. 懒加载（推荐）
object LazyLoadDemo extends App{
import java.io.PrintWriter
trait Logger{
def log(msg: String): Unit
}
trait FileLogger extends Logger {
val fileName: String
lazy val fileOutput = new PrintWriter(fileName: String)
def log(msg: String): Unit ={
fileOutput.print(msg)
fileOutput.flush()
}
}
class Person
class Student(var name: String) extends Person with FileLogger{
override val fileName: String = "file.log"
}
val s = new Student("Win")
s.log("#")
s.log("Lazy demo")
}
最新文章
- 初学者-PHP笔记
- ipad
- 基于Qt5.5.0的sql数据库、SDK_tts文本语音朗读的CET四六级单词背诵系统软件的编写V1.0
- smdkv210
- SQLServer异常捕获
- RESTful API 设计最佳实践(转)
- Android之提交数据到服务端方法简单封装
- C语言随笔_区分=与==
- php读取excel文档内容（转载）
- Cookie禁用 获取session
- A.01.11—模块的输出—输出复用和可配
- Hadoop学习笔记（五）：java开发MapReduce
- new Vue 发生了什么
- https://github.com/Lushenggang/show-pdf在线浏览pdf文件在线浏览pdf文件
- ASP.NET 之 MVC框架及搭建
- SpringData修改和删除操作
- eigen安装
- leetcode-209-长度最小的子数组
- java基本编译
- 浅谈ES6基础——Promise