五、scala面向对象-类

1、类

一、定义类

##定义并调用
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

咱们在用Java的时候常常把一些字段定义为private类型来完成封装，这样外界就没法访问。
若是外界访问或者修改该字段的时候，只能经过该字段提供的getter和setter方法来实现。
在Scala中是没有getter和setter一说的。
用了value 和 value_= 来分别代替了getter和setter。


■ 若是字段是私有的，则getter和setter方法也是私有的   

　　就是说明，当咱们定义一个字段为私有的时候，自动生成的getter和setter也不能被外界使用了。

       就是咱们不能在外界使用  点+字段  的方式来访问或者修改该字段了。

　　咱们能够经过本身改写scala的getter和setter来完成对私有变量的访问和修改，如上述。

■ 若是字段是val，则只有getter方法被生成 

　　当咱们须要getter和setter的时候，能够定义变量为var

　　当咱们只须要getter不须要setter的时候，咱们能够定义变量为val

■ 若是你不须要任何getter或setter，能够将字段声明为private[this]

咱们要么在对私有变量设置访问方法的时候
要么加上getter方法（对val字段而言）要么加上getter和setter方法（对var字段而言）
但在Scala中，你不能实现只写属性，即带有setter但不带getter的属性。



##
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、自定义getter  setter

//若是只是但愿拥有简单的getter和setter方法，那么就按照scala提供的语法规则，根据需求为field选择合适的修饰符就好：var、val、private、private[this]
//可是若是但愿可以本身对getter与setter进行控制，则能够自定义getter与setter方法
//自定义setter方法的时候必定要注意scala的语法限制，签名、=、参数间不能有空格


##
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、仅暴露field的getter方法

//若是你不但愿field有setter方法，则能够定义为val，可是此时就不再能更改field的值了
//可是若是但愿可以仅仅暴露出一个getter方法，而且还能经过某些方法更改field的值，那么须要综合使用private以及自定义getter方法
//此时，因为field是private的，因此setter和getter都是private，对外界没有暴露；本身能够实现修改feld值的方法；本身能够覆盖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

//若是将field使用private来修饰，那么表明这个field是类私有的，在类的方法中，能够直接访问类的其余对象的private field
//这种状况下，若是不但愿field被其余对象访问到，那么可使用private[this]，意味着对象私有的field，只有本对象内能够访问到



##
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风格的getter和setter方法

//Scala的getter和setter方法的命名与java是不一样的，是field和field_=的方式
//若是要让scala自动生成java风格的getter和seter方法，只要给field添加@BeanProperty注解便可
//此时会生成4个方法，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

###在主构造函数方式加注解

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、辅助constructor

Scala中，能够给类定义多个辅助constructor，相似于Java中的构造函数重载，辅助constructor之间能够互相调用，并且必须第一行调用主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是与类名放在一块儿的，与java不一样
//并且类中，没有定义在任何方法或者是代码块之中的代码，就是主constructor的代码，这点感受没有java那么清晰

###
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中还能够经过使用默认参数，来给参数默认的值。

###
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传入的参数什么修饰都没有，好比name:String，那么若是类内部的方法使用到了，则会声明为private[this] name，
不然没有该field，就只能被constructor代码使用而已。

###
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、内部类

Scala中，一样能够在类中定义内部类，可是与Java不一样的是，每一个外部类的对象的内部类，都是不一样的类。

c2.Student类，c1.Student类，是不一样的外部类的实例的不一样的类。


###
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
                      ^