構(gòu)造函數(shù)

• 主構(gòu)造函數(shù)如果不加val 和var ,只是構(gòu)造傳參而已，不屬于類(lèi)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(lèi)型的主構(gòu)造變量會(huì)升級(jí)為私有變量。同時(shí)生成一個(gè)公開(kāi)的訪問(wèn)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(xiě)在主構(gòu)造方法里和類(lèi)里面在可見(jiàn)性和可變性上沒(méi)有區(qū)別，唯一的區(qū)別在于構(gòu)造函數(shù)

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(gòu)造函數(shù)

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(lèi)繼承trait，主構(gòu)造函數(shù)不能作為接口的實(shí)現(xiàn).但是抽象類(lèi)和樣例類(lèi)可以
• var 類(lèi)型的變量可以被 val類(lèi)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(lèi)，抽象類(lèi)，普通類(lèi)繼承抽象類(lèi)，抽象類(lèi)的主構(gòu)造函數(shù)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(lèi)覆蓋后，才能對(duì)外可見(jiàn).其他的可見(jiàn)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(jié)

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