五、scala面向對象-類

1、類

一、定義類

##定義並調用
scala> :paste
// Entering paste mode (ctrl-D to finish)

class HelloWord {
  private var name = "Leo"
  def sayHello() {print("Hello, " + name)}
  def getName = name
}

// Exiting paste mode, now interpreting.

defined class HelloWord

scala> val helloWord = new HelloWord
helloWord: HelloWord = HelloWord@eba64a9

scala> helloWord.sayHello()
Hello, Leo
scala> 

scala> print(helloWord.getName)
Leo

二、getter和setter

咱們在用Java的時候常常把一些字段定義爲private類型來完成封裝，這樣外界就沒法訪問。
若是外界訪問或者修改該字段的時候，只能經過該字段提供的getter和setter方法來實現。
在Scala中是沒有getter和setter一說的。
用了value 和 value_= 來分別代替了getter和setter。


■ 若是字段是私有的，則getter和setter方法也是私有的   

　　就是說明，當咱們定義一個字段爲私有的時候，自動生成的getter和setter也不能被外界使用了。

       就是咱們不能在外界使用  點+字段  的方式來訪問或者修改該字段了。

　　咱們能夠經過本身改寫scala的getter和setter來完成對私有變量的訪問和修改，如上述。

■ 若是字段是val，則只有getter方法被生成 

　　當咱們須要getter和setter的時候，能夠定義變量爲var

　　當咱們只須要getter不須要setter的時候，咱們能夠定義變量爲val

■ 若是你不須要任何getter或setter，能夠將字段聲明爲private[this]

咱們要麼在對私有變量設置訪問方法的時候
要麼加上getter方法（對val字段而言）要麼加上getter和setter方法（對var字段而言）
但在Scala中，你不能實現只寫屬性，即帶有setter但不帶getter的屬性。



##
scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student {
  var name = "leo"
}

// Exiting paste mode, now interpreting.


scala> val s = new Student
s: Student = Student@4cdbe50f

scala> s.name
res2: String = leo

scala> s.name = "jack"
s.name: String = jack

scala> s.name
res3: String = jack

三、自定義getter  setter

//若是隻是但願擁有簡單的getter和setter方法，那麼就按照scala提供的語法規則，根據需求爲field選擇合適的修飾符就好：var、val、private、private[this]
//可是若是但願可以本身對getter與setter進行控制，則能夠自定義getter與setter方法
//自定義setter方法的時候必定要注意scala的語法限制，簽名、=、參數間不能有空格


##
scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student {
  private var myName = "leo"
  def name = "your name is " + myName
  def name_=(newName: String) {
    print("you cannot edit your name!")
  }
}

// Exiting paste mode, now interpreting.

defined class Student

scala> val s = new Student
s: Student = Student@52f759d7

scala> s.name
res4: String = your name is leo

scala> s.name = "leo1"
you cannot edit your name!s.name: String = your name is leo

四、僅暴露field的getter方法

//若是你不但願field有setter方法，則能夠定義爲val，可是此時就不再能更改field的值了
//可是若是但願可以僅僅暴露出一個getter方法，而且還能經過某些方法更改field的值，那麼須要綜合使用private以及自定義getter方法
//此時，因爲field是private的，因此setter和getter都是private，對外界沒有暴露；本身能夠實現修改feld值的方法；本身能夠覆蓋getter方法



##
scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student {
  private var myName = "leo"
  
  def updateName(newName: String) {
    if (newName == "leo1") myName = newName
    else println("not accept this new name, " + newName)
  }
  
  def name = myName
}

// Exiting paste mode, now interpreting.

defined class Student

scala> val s = new Student
s: Student = Student@4aa8f0b4

scala> s.updateName("leo1")

scala> s.updateName("leo2")
not accept this new name, leo2

scala> s.name
res2: String = leo1

五、private[this]的使用

//若是將field使用private來修飾，那麼表明這個field是類私有的，在類的方法中，能夠直接訪問類的其餘對象的private field
//這種狀況下，若是不但願field被其餘對象訪問到，那麼可使用private[this]，意味着對象私有的field，只有本對象內能夠訪問到



##
scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student {
  private[this] var myAge = 0
  def age_=(newAge: Int) {
  if (newAge > 0) myAge = newAge
  else println("illegal age!!")
  }
  def age = myAge
  def older(s: Student) = {
  myAge > s.myAge
  }
}

// Exiting paste mode, now interpreting.

<console>:22: error: value myAge is not a member of Student
         myAge > s.myAge
                   ^

六、Java風格的getter和setter方法

//Scala的getter和setter方法的命名與java是不一樣的，是field和field_=的方式
//若是要讓scala自動生成java風格的getter和seter方法，只要給field添加@BeanProperty註解便可
//此時會生成4個方法，name:String、name_=（newValue:String):Unit、getName()：String、setName（newValue:String）：Unit



###

scala> import scala.reflect.BeanProperty
<console>:10: error: object BeanProperty is not a member of package reflect
        import scala.reflect.BeanProperty
               ^

scala> import scala.beans.BeanProperty
import scala.beans.BeanProperty

scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student {
   @BeanProperty var name: String = _
}

// Exiting paste mode, now interpreting.

defined class Student

scala> val s = new Student
s: Student = Student@59690aa4

scala> s.setName("leo")

scala> s.getName()
res1: String = leo

scala> s.setName("jack")

scala> s.getName()
res3: String = jack

###在主構造函數方式加註解

scala> class Student(@BeanProperty var name: String)
defined class Student

scala> val s = new Student("leo")
s: Student = Student@5f9d02cb

scala> s.getName()
res4: String = leo

scala> s.setName("jen")

scala> s.getName()
res6: String = jen

七、輔助constructor

Scala中，能夠給類定義多個輔助constructor，相似於Java中的構造函數重載，輔助constructor之間能夠互相調用，並且必須第一行調用主constructor。


###
scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student {
  private var name = ""
  private var age = 0
  def this(name: String) {
    this()
    this.name = name
  }
  def this(name: String, age:Int) {
    this(name)
    this.age = age
  }
}

// Exiting paste mode, now interpreting.

defined class Student

scala> val s1 = new Student
s1: Student = Student@78b729e6

scala> val s1 = new Student("leo")
s1: Student = Student@1fe20588

scala> val s1 = new Student("leo",30)
s1: Student = Student@647e447

八、主constructor

//Scala中， 主constructor是與類名放在一塊兒的，與java不一樣
//並且類中，沒有定義在任何方法或者是代碼塊之中的代碼，就是主constructor的代碼，這點感受沒有java那麼清晰

###
scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student(val name: String, val age: Int) {
  println("your name is " + name + ", your age is " + age)
}

// Exiting paste mode, now interpreting.

defined class Student

scala> val s = new Student("leo", 30)
your name is leo, your age is 30
s: Student = Student@6069db50



主construntor中還能夠經過使用默認參數，來給參數默認的值。

###
scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student(val name: String = "leo", val age: Int = 30) {
  println("your name is " + name + ", your age is " + age)
}

// Exiting paste mode, now interpreting.

defined class Student

scala> val s = new Student
your name is leo, your age is 30
s: Student = Student@682b2fa



若是主constructor傳入的參數什麼修飾都沒有，好比name:String，那麼若是類內部的方法使用到了，則會聲明爲private[this] name，
不然沒有該field，就只能被constructor代碼使用而已。

###
scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student(name: String, age: Int) {
  println("your name is " + name + ", your age is " + age)
}

// Exiting paste mode, now interpreting.

defined class Student
warning: previously defined object Student is not a companion to class Student.
Companions must be defined together; you may wish to use :paste mode for this.

scala> val s = new Student("leo", 30)
your name is leo, your age is 30
s: Student = Student@58a9760d

九、內部類

Scala中，一樣能夠在類中定義內部類，可是與Java不一樣的是，每一個外部類的對象的內部類，都是不一樣的類。

c2.Student類，c1.Student類，是不一樣的外部類的實例的不一樣的類。


###
scala> :paste
// Entering paste mode (ctrl-D to finish)

import scala.collection.mutable.ArrayBuffer

class Class {
  class Student(val name: String) 
  val students = new ArrayBuffer[Student]()
  def getStudent(name: String) = {
    new Student(name) 
  } 
}

// Exiting paste mode, now interpreting.

import scala.collection.mutable.ArrayBuffer
defined class Class

scala> val c1 = new Class
c1: Class = Class@50b5ac82

scala> val s1 = c1.getStudent("leo")
s1: c1.Student = Class$Student@45099dd3

scala> c1.students += s1
res0: c1.students.type = ArrayBuffer(Class$Student@45099dd3)

scala> val c2 = new Class
c2: Class = Class@2783717b

scala> val s2 = c2.getStudent("leo")
s2: c2.Student = Class$Student@7e985ce9

scala> c1.students += s2
<console>:16: error: type mismatch;
 found   : c2.Student
 required: c1.Student
       c1.students += s2
                      ^