Scala面向对象
1.面向对象概述
封装：属性方法封装到类中
继承：父类和子类直接的关系
多态：***** 父类引用指向子类对象 精髓所在，开发框架的基石
2.类的定义和使用
package com.gwf.scala.course04
object SimpleObjectApp {def main(args: Array[String]): Unit = {
val person = new People()
person.name = "Messi"println(person.name+" "+person.age)
println("invoke eat method "+person.eat)
person.watchFootball("Barcelona")
person.printInfo()
}class People{
var name:String = _ //_代表占位符val age = 10// 私有变量，外部不能访问，[]里的this代表访问权限，可以填当前所在包，则包内可以访问private [this] var gender:String = "male"def printInfo(): Unit ={
println(gender)
}def eat():String={
name + "eat ....."}def watchFootball(teamName: String)={
println(name+"is watching match of "+teamName)
}
}
}scala> var d:Double = _ d: Double = 0.0scala> val i:Int = _ <console>:11: error: unbound placeholder parameter val i:Int = _ ^ scala> var i:Int = _ i: Int = 0scala> var s:String = _ s: String = nullscala>
3.主构造器和附属构造器
// 主构造器,如果不加val/var修饰符则默认是private[this] val 类型class Person(val name:String,val age:Int,other:String){
println("Person Constructor enter...")
val school = "ustc"var gender:String = _
def getOther(): String = other
def this(name:String,age:Int,other:String,gender:String){this(name,age,other) // 附属构造器的第一行必须调用主构造器或者其他构造器this.gender = gender
}
println("Person Constructor leave...")
}4.继承
// 子类继承父类，父类的属性在子类构造函数中可以不加val/var声明，子类特有的属性必须要加，否则也会变成private[this] valclass Student(name:String,age:Int,other:String,val school:String) extends Person(name,age,other){
}5.重写
class Student(name:String,age:Int,other:String,val school:String) extends Person(name,age,other){// 重写必须加overrideoverride val country: String = "USA"// $代表thisoverride def toString = s"Student($country, $school)"}6.抽象类
/**
* 类的一个或者多个方法没有完整的实现(只有定义，没有实现)
*/abstract class Person2{
def speak
var name:String
var age:Int
}/**
* 普通了继承抽象类要实现未实现的抽象方法和抽象属性
*/class Student2 extends Person2{
override def speak: Unit = println("speak")
override var name: String = _
override var age: Int = _
}7.伴生类和伴生对象
/**
* 如果有一个class,还有一个与class同名的object
* 那么就称称这个个object是class的伴生対象, class是object的伴生类，两者相辅相成
*/class ApplyTest{
}
object ApplyTest{
}8.Apply 方法
package com.gwf.scala.course04
object ApplyApp {def main(args: Array[String]): Unit = {for(i <- 1 to 10){
ApplyTest.incr
}
println("count:"+ApplyTest.count) // 10 说明object本身就是一个单例对象println("~~~~~~~~~~~~~")
val b = ApplyTest() // ==>Object.println("~~~~~~~~~~~~~")
val c = new ApplyTest()
println(c)
c() // ==>Class.// 类名() ===> Object.apply// 对象() ===> Class.apply}
}/**
* 如果有一个class,还有一个与class同名的object
* 那么就称称这个个object是class的伴生対象, class是object的伴生类，两者相辅相成
*/class ApplyTest{def apply()= {
println("Class ApplyTest apply...")
}
}
object ApplyTest{
println("Object ApplyTest enter...")
var count = 0def incr = {
count = count + 1}// 最佳实践:在0bject的apply方法中去new Classdef apply()= {
println("Object ApplyTest apply...")
}
println("Object ApplyTest leave...")
}9.case class
package com.gwf.scala.course04// 通常用到模式匹配里object CaseClassApp {def main(args: Array[String]): Unit = {
println(Dog("wangcai").name)
}
}case class Dog(name:String)10.Trait
Trait 类似于java的接口，但是可以集成抽象类，并实现其抽象方法。
// Triat多集成：XXX extends ATrait with BTraitclass SparkConf(loadDefaults: Boolean) extends Cloneable with Logging with Serializable {
作者：Meet相识_bfa5
链接：https://www.jianshu.com/p/ab06b0222b14
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