单例模式

单例：希望某个类只存在一个使用的对象，而不管有多少个调用者在使用它，就是单例的概念。

package base

object Singleton extends App {
  val aloneC1 = AloneObj.getAloneCInstance
  val aloneC2 = AloneObj.getAloneCInstance
  aloneC1.addOne
  aloneC2.addOne
  println(aloneC1.getPrice, aloneC2.getPrice)
}

object AloneObj {
  private var aloneC: AloneC = null

  def getAloneCInstance: AloneC = {

    // 第一次掉用时创建实例
    if (this.aloneC == null) this.aloneC = new AloneC()

    this.aloneC
  }

}

// 需要单例的类
class AloneC {
  private var price = 0.0

  def addOne = {
    price += 1
  }

  def add(num: Double): Unit = {
    price += num
  }

  def getPrice = price
}

转载于:https://www.cnblogs.com/studyNotesSL/p/11443783.html