構造函數

• 主構造函數如果不加val 和var ,只是構造傳參而已，不屬于類變量

class Demo(name: String)? sbt_demo javap -p Demo Compiled from "Demo.scala" public class Demo {public Demo(java.lang.String); }

• 加了var 和val類型的主構造變量會升級為私有變量。同時生成一個公開的訪問方法。而且val 的變量是final,var不是。

class Demo(name: String, var age: Int, val home: String)? sbt_demo javap -p Demo* Compiled from "Demo.scala" public class Demo {private int age;public int age();public void age_$eq(int);private final java.lang.String home;public java.lang.String home();public Demo(java.lang.String, int, java.lang.String); }

• 成員變量寫在主構造方法里和類里面在可見性和可變性上沒有區別，唯一的區別在于構造函數

class Demo(name: String) {var age: Int = 0val home: String = "ok" }? sbt_demo javap -p Demo* Compiled from "Demo.scala" public class Demo {private int age;public int age();public void age_$eq(int);private final java.lang.String home;public java.lang.String home();public Demo(java.lang.String); }

trait

• trait不能有構造函數

trait people(name:String) // error trait people(val name:String) // error trait people(var name:String) // error trait people{name:String} // error trait people{val name:String} // right trait people{var name:String} // right

trait的繼承

• 普通的類繼承trait，主構造函數不能作為接口的實現.但是抽象類和樣例類可以
• var 類型的變量可以被 val類型的變量覆蓋。反之不行

trait people {val name: Stringvar age: Int }case class son(name: String, age: Int) extends people // right abstract class son(name: String, age: Int) extends people // right class son(name: String, age: Int) extends people // error class son(val name: String, var age: Int) extends people // right class son(val name: String, val age: Int) extends people // right class son(var name: String, val age: Int) extends people // error

abstract class

• 樣例類，抽象類，普通類繼承抽象類，抽象類的主構造函數可以被覆蓋

abstract class people(home: String) {val name: Stringvar age: Int }case class son(name: String, age: Int, home: String) extends people(home) // right abstract class son(name: String, age: Int, home: String) extends people(home) // right class son(val name: String, var age: Int, home: String) extends people(home) // right

• 只有樣例類覆蓋后，才能對外可見.其他的可見性，繼承者和被繼承著保持一致

abstract class people(var home: String) {val name: Stringvar age: Int }case class son(name: String, age: Int, override var home: String) extends people(home) // right abstract class son(name: String, age: Int, home: String) extends people(home) // right class son(val name: String, var age: Int, home: String) extends people(home) // right

總結

以上是生活随笔為你收集整理的scala trait ,abstract class,case class,class 的一些琐碎注意事项,仅针对3.0以下的全部內容，希望文章能夠幫你解決所遇到的問題。

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