当scala.collection.mutable.Map是抽象的时，我如何扩展它？

import scala.collection.mutable

class MyMap extends mutable.Map[String, Int] {
  private val underlyingMap = mutable.Map[String, Int]()

  override def get(key: String): Option[Int] = underlyingMap.get(key)

  override def put(key: String, value: Int): Option[Int] = underlyingMap.put(key, value)

  override def remove(key: String): Option[Int] = underlyingMap.remove(key)

  override def iterator: Iterator[(String, Int)] = underlyingMap.iterator

  // 添加额外的方法
  def customMethod(): Unit = {
    // 自定义的逻辑
  }
}