apply的基本使用和实现单例模式

package level02

/*
* apply
* 作用：写在伴生对象中，就可以允许创建对象的时候，省略new
* */
object Class10 {
    // 伴生类
    class Logger(){}
    // 伴生对象
    object Logger {
        fun apply():Logger = {
            println("logger......")
            new Logger()
        }
    }

    fun main(args: Array[String]): Unit = {
        // 创建一个类的对象
        // val log1 = new Logger()
        // 在伴生对象中提供了apply方法，那么这里就会自动去调用它
        val log1 = Logger()
        val log2 = Logger()
        println(log1 == log2) // 这里会输出什么？
    }
}

package level02

object class16 {
  class Point(var x: Double, var y: Double) {
    def whereAmI(): String = {
      if (x > 0 && y > 0) "第一象限"
      else if (x < 0 && y > 0) "第二象限"
      else if (x < 0 && y < 0) "第三象限"
      else if (x > 0 && y < 0) "第四象限"
      else if (x == 0 && y == 0) "原点"
      else if (x == 0) "在y轴上"
      else "在y轴上"
    }

    def getDist(): Double = {
      Math.sqrt(x * x + y * y)
    }

    def fromPoint(other: Point): Double = {
      val dx = other.x - x
      val dy = other.y - y
      Math.sqrt(dx * dx + dy * dy)
    }

    override def toString: String = s"Point(${x}, ${y})"

    override def equals(obj: Any): Boolean = {
      obj match {
        case other: Point => this.x == other.x && this.y == other.y
        case _ => false
      }
    }

    class LabelPoint(val label: String, x: Double, y: Double) extends Point(x, y) {
      override def toString: String = s"LabelPoint($label, $x, $y)"
    }

    def main(args: Array[String]): Unit = {
      // 测试
      val p1 = new Point(1.0, 1.0)
      val p2 = new Point(1.0, 1.0)
      println(p1.whereAmI())
      println(p1.getDist())
      println(p1.fromPoint(p2))
      println(p1 == p2)
    }
  }
}