Scala入门与进阶（四）- Scala面向对象

4. 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 = _ //_表明占位符
val age = 10

// 私有变量，外部不能访问，[]里的this表明访问权限，能够填当前所在包，则包内能够访问
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)
}

}
}
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scala> var d:Double = _
d: Double = 0.0

scala> val i:Int = _
<console>:11: error: unbound placeholder parameter
val i:Int = _
^

scala> var i:Int = _
i: Int = 0

scala> var s:String = _
s: String = null

scala>
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3.主构造器和附属构造器

// 主构造器,若是不加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余构造器
this.gender = gender
}
println("Person Constructor leave...")

}
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4.继承

// 子类继承父类，父类的属性在子类构造函数中能够不加val/var声明，子类特有的属性必需要加，不然也会变成private[this] val
class Student(name:String,age:Int,other:String,val school:String) extends Person(name,age,other){

}
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5.重写

class Student(name:String,age:Int,other:String,val school:String) extends Person(name,age,other){

// 重写必须加override
override val country: String = "USA"

// $表明this
override def toString = s"Student($country, $school)"
}
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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 = _
}
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7.伴生类和伴生对象

/** * 若是有一个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，二者相辅相成 */
class ApplyTest{

}

object ApplyTest{

}
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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自己就是一个单例对象

println("~~~~~~~~~~~~~")
val b = ApplyTest() // ==>Object.

println("~~~~~~~~~~~~~")
val c = new ApplyTest()
println(c)
c() // ==>Class.

// 类名() ===> Object.apply
// 对象() ===> Class.apply
}
}

/** * 若是有一个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，二者相辅相成 */
class ApplyTest{
def apply()= {
println("Class ApplyTest apply...")
}
}

object ApplyTest{

println("Object ApplyTest enter...")

var count = 0

def incr = {
count = count + 1
}

// 最佳实践:在0bject的apply方法中去new Class
def apply()= {
println("Object ApplyTest apply...")
}

println("Object ApplyTest leave...")

}
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9.case class

package com.gwf.scala.course04

// 一般用到模式匹配里
object CaseClassApp {
def main(args: Array[String]): Unit = {
println(Dog("wangcai").name)
}
}

case class Dog(name:String) 复制代码

10.Trait

Trait 相似于java的接口，可是能够集成抽象类，并实现其抽象方法。

// Triat多集成：XXX extends ATrait with BTrait
class SparkConf(loadDefaults: Boolean) extends Cloneable with Logging with Serializable {

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