Scala的伴生类、伴生对象与单例对象和apply的介绍

1、代码如下：

package com.yy.oop

/**
 * 伴生类和<span style="background-color: rgb(160, 255, 255);">伴生对象</span>
 * class Student是<span style="background-color: rgb(160, 255, 255);">伴生对象</span>Object Student的伴生类
 * object Student是伴生类class Student的<span style="background-color: rgb(160, 255, 255);">伴生对象</span> 
 */


//伴生类
class Student(var name:String,var address:String){
  
  private var phone="110"
  //直接访问<span style="background-color: rgb(160, 255, 255);">伴生对象</span>的私有成员
  def infoCompObj() = println("伴生类中访问<span style="background-color: rgb(160, 255, 255);">伴生对象</span>：" + Student.sno)
}

//<span style="background-color: rgb(160, 255, 255);">伴生对象</span>
object Student {
  
  private var sno:Int = 100
  def incrementSno()={
    
    sno += 1 //加1
    sno  //返回sno
  }
  def main(args: Array[String]): Unit = {
    
    println("单例对象：" + Student.incrementSno()) //单例对象
    
    //实例化伴生类
    val obj = new Student("yy","bj")
    obj.infoCompObj();
  }
}

2、结果如下

单例对象：101
伴生类中访问<span style="background-color: rgb(160, 255, 255);">伴生对象</span>：101

3、scala apply 

package com.yy.oop

/**
 * 伴生类和<span style="background-color: rgb(160, 255, 255);">伴生对象</span>
 * class Student是<span style="background-color: rgb(160, 255, 255);">伴生对象</span>Object Student的伴生类
 * object Student是伴生类class Student的<span style="background-color: rgb(160, 255, 255);">伴生对象</span> 
 */


//伴生类
class Student(var name:String,var address:String){
  
  private var phone="110"
  //直接访问<span style="background-color: rgb(160, 255, 255);">伴生对象</span>的私有成员
  def infoCompObj() = println("伴生类中访问<span style="background-color: rgb(160, 255, 255);">伴生对象</span>：" + Student.sno)
}

//<span style="background-color: rgb(160, 255, 255);">伴生对象</span>
object Student {
  
  private var sno:Int = 100
  def incrementSno()={
    
    sno += 1 //加1
    sno  //返回sno
  }
  
  //定义apply方法,实例化伴生类
  def apply(name1:String,address1:String)= new Student(name1,address1)
  
  
  def main(args: Array[String]): Unit = {
    
    println("单例对象：" + Student.incrementSno()) //单例对象
    
    //实例化伴生类
    val obj = new Student("yy","bj")
    obj.infoCompObj();
    
    println("通过<span style="background-color: rgb(160, 255, 255);">伴生对象</span>的apply方法访问伴生类成员:")
    val obj2 = Student("yy_apply","bj_apply") //实际是通过apply方法进行了对象实例化，避免了手动new对象
    println(obj2.name)
    println(obj2.address)
  }
}

结果如下：

单例对象：101
伴生类中访问<span style="background-color: rgb(160, 255, 255);">伴生对象</span>：101
通过<span style="background-color: rgb(160, 255, 255);">伴生对象</span>的apply方法访问伴生类成员:
yy_apply
bj_apply