学习scala

https://docs.scala-lang.org/zh-cn/tour/tour-of-scala.html

1. main,class,object

The main method can only be written in objectdefined file
object和class啥区别：
Review a question：java中有一个知识点 静态
分号可有可无
scalais a package-level distinction,The class name can be inconsistent with the file name

2. scalaThe filename and classname can be different

3. You can write more than one in a fileobject
   

4. bare code andmainThe order of execution of the function code：
   

5. 使用s来拼接字符串
   
6. class和object的执行顺序：
   

7. scala是一门真正的面向对象的编程语言
   

8. option类型：getOrElse,优化null返回值的if判断,降低cpu开销

源码

package com.zxl.bigdata.scala


//约等于 static 单例对象
//static
//单例 new scalaThe compiler is very user-friendly Let you people write a lot less code
object ooxx {
    

  // private val xo:xxoo = new xxoo()
  private val xo = new ooxx(11)
  // Integer num = 0;
  // var/val var:变量 val常量 取代了final
  /* var a=3 a=4 val b=4 b=5*/

  private val name = "object:zhangsan"


  println("ooxx....up")

  def main(args: Array[String]): Unit = {
    
    println("hello from ooxx")
    xo.printMsg()
  }

  println("ooxx....down")

}

//类里,Exposed code is default constructed.有默认构造
//Personalized construction！！
//The parameters in the class name constructor are the member properties of the class,且默认是val类型,且默认是private
//Only parameters in the classname construct can be set tovar,Parameters in other method functions are allval类型的,and is not allowed to be set tovar类型
class ooxx(sex: String) {
    


  var name = "class:zhangsan"

  def this(xname: Int) {
    
    //The default constructor must be invoked
    this("abc")


  }

  var a: Int = 3

  // private val value = new ooxx()

  println(s"ooxx....up$a....")

  def printMsg(): Unit = {
    
    println(s"sex: ${
      ooxx.name}")
  }

  println(s"ooxx....up${
      a + 4}")
}