Scala03-面向对象

2019-04-25

类

类是某一种或者某一类东西的抽象（人、猫、狗–>生物）

class

class People(){
  var name:String = ""
  var city:String = ""

  def eat(): Unit ={
    println(this.name + "eat ....")
  }

  def py(pyName:String): Unit ={
    println(this.name + "正在跟" + pyName + "xxxx...")
  }
}

----------
- 通过class关键字进行类的定义
- 属性：name、city
- 方法：eat、py

调用

    val people = new People()
    people.name = "大树"
    people.city = "北京"
    people.eat()

-----------
- 对象通过new关键字进行新建
- 属性和方法的调用通过.

占位符

var sex = _

Double:0.0
Int:0
String:null
Boolean:false
-------
- 定义属性的时候使用_代表占位符
- 如果使用了占位符必须要声明变量的类型
- 使用占位符会有默认值

链式编程的实现

实现目标：val conf = new SparkConf().setAppName(appName).setMaster(master)

---------------------
class SparkConf{
  var setting = new ConcurrentHashMap[String,String]

  // 底层是一个map
  private[this] def set(key:String,value:String): SparkConf ={
    setting.put(key,value)
    this
  }

  def setMaster(master:String): SparkConf ={
    set("spark.master",master)
  }

  def setAppName(name:String): SparkConf ={
    set("spark.app.name",name)
  }

  def printInfo(): Unit ={
    println(setting.get("spark.master") + setting.get("spark.app.name"))
  }
}

----------------------
    val sparkConf = new SparkConf()
    sparkConf.setMaster("yarn").setAppName("SparkConfApp")
    sparkConf.printInfo

----------------------
- 这里我们的setXXX函数返回了一个当前对象，这样我们就能够实现链式编程的核心
- set函数我们使用了private[this]关键字进行了定义，这样set方法就只能在本类调用，在外部就没办法进行调用了

类-源码结合

pom.xml

<spark.version>2.4.0</spark.version>

    <!--sparkCore依赖-->
    <dependency>
      <groupId>org.apache.spark</groupId>
      <artifactId>spark-core_2.11</artifactId>
      <version>${spark.version}</version>
    </dependency>

SparkConf.scala

  private[spark] def set(key: String, value: String, silent: Boolean): SparkConf = {
    if (key == null) {
      throw new NullPointerException("null key")
    }
    if (value == null) {
      throw new NullPointerException("null value for " + key)
    }
    if (!silent) {
      logDeprecationWarning(key)
    }
    settings.put(key, value)
    this
  }

  /**
   * The master URL to connect to, such as "local" to run locally with one thread, "local[4]" to
   * run locally with 4 cores, or "spark://master:7077" to run on a Spark standalone cluster.
   */
  def setMaster(master: String): SparkConf = {
    set("spark.master", master)
  }

-----------
这里可以看到跟我们demo的写法是一致的

构造器方法

主构造器

class Person(val name:String,val city:String){
  println("Person Enter...")

  def eat(): Unit ={
    println(name + "eat....")
  }
}

    val person = new Person("大树","北京")
    person.eat()

------------
Person Enter...
大树eat....

- 在class后面的内容就是主构造器
- 我们在定义类的时候指定了属性，就可以通过传参的方式直接构建对象

附属构造器

  var age:Int = _

  // 附属构造器
  def this(name:String,city:String,age:Int){
    this(name,city)
    this.age = age
  }

val person2 = new Person("小花","盐城",18)
--------------------
附属构造器必须调用主构造器或者其他构造器