Scala入门与进阶（四）- Scala面向对象

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 = 0.0

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>

// 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...")

}

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

}

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"

// $代表this
override def toString = s"Student($country, $school)"
}

/**
* 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 = _
}

/**
* 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{

}

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 = 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...")

}

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)

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