Scala example source code file (HashMap.scala)

This example Scala source code file (HashMap.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

a, abstractiterator, b, c, collection, defaultentry, entry, hashmap, iterator, mutable, none, option, parallel

The HashMap.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection
package mutable

import generic._
import scala.collection.parallel.mutable.ParHashMap

/** This class implements mutable maps using a hashtable.
 *
 *  @since 1
 *  @see [[http://docs.scala-lang.org/overviews/collections/concrete-mutable-collection-classes.html#hash_tables "Scala's Collection Library overview"]]
 *  section on `Hash Tables` for more information.
 *
 *  @tparam A    the type of the keys contained in this hash map.
 *  @tparam B    the type of the values assigned to keys in this hash map.
 *
 *  @define Coll `mutable.HashMap`
 *  @define coll mutable hash map
 *  @define thatinfo the class of the returned collection. In the standard library configuration,
 *    `That` is always `HashMap[A, B]` if the elements contained in the resulting collection are
 *    pairs of type `(A, B)`. This is because an implicit of type `CanBuildFrom[HashMap, (A, B), HashMap[A, B]]`
 *    is defined in object `HashMap`. Otherwise, `That` resolves to the most specific type that doesn't have
 *    to contain pairs of type `(A, B)`, which is `Iterable`.
 *  @define bfinfo an implicit value of class `CanBuildFrom` which determines the
 *    result class `That` from the current representation type `Repr`
 *    and the new element type `B`. This is usually the `canBuildFrom` value
 *    defined in object `HashMap`.
 *  @define mayNotTerminateInf
 *  @define willNotTerminateInf
 */
@SerialVersionUID(1L)
class HashMap[A, B] private[collection] (contents: HashTable.Contents[A, DefaultEntry[A, B]])
extends AbstractMap[A, B]
   with Map[A, B]
   with MapLike[A, B, HashMap[A, B]]
   with HashTable[A, DefaultEntry[A, B]]
   with CustomParallelizable[(A, B), ParHashMap[A, B]]
   with Serializable
{
  initWithContents(contents)

  type Entry = DefaultEntry[A, B]

  override def empty: HashMap[A, B] = HashMap.empty[A, B]
  override def clear() { clearTable() }
  override def size: Int = tableSize

  def this() = this(null)

  override def par = new ParHashMap[A, B](hashTableContents)

  // contains and apply overridden to avoid option allocations.
  override def contains(key: A): Boolean = findEntry(key) != null

  override def apply(key: A): B = {
    val result = findEntry(key)
    if (result eq null) default(key)
    else result.value
  }

  def get(key: A): Option[B] = {
    val e = findEntry(key)
    if (e eq null) None
    else Some(e.value)
  }

  override def put(key: A, value: B): Option[B] = {
    val e = findOrAddEntry(key, value)
    if (e eq null) None
    else { val v = e.value; e.value = value; Some(v) }
  }

  override def update(key: A, value: B): Unit = put(key, value)

  override def remove(key: A): Option[B] = {
    val e = removeEntry(key)
    if (e ne null) Some(e.value)
    else None
  }

  def += (kv: (A, B)): this.type = {
    val e = findOrAddEntry(kv._1, kv._2)
    if (e ne null) e.value = kv._2
    this
  }

  def -=(key: A): this.type = { removeEntry(key); this }

  def iterator = entriesIterator map (e => ((e.key, e.value)))

  override def foreach[C](f: ((A, B)) => C): Unit = foreachEntry(e => f((e.key, e.value)))

  /* Override to avoid tuple allocation in foreach */
  override def keySet: scala.collection.Set[A] = new DefaultKeySet {
    override def foreach[C](f: A => C) = foreachEntry(e => f(e.key))
  }

  /* Override to avoid tuple allocation in foreach */
  override def values: scala.collection.Iterable[B] = new DefaultValuesIterable {
    override def foreach[C](f: B => C) = foreachEntry(e => f(e.value))
  }

  /* Override to avoid tuple allocation */
  override def keysIterator: Iterator[A] = new AbstractIterator[A] {
    val iter    = entriesIterator
    def hasNext = iter.hasNext
    def next()  = iter.next().key
  }

  /* Override to avoid tuple allocation */
  override def valuesIterator: Iterator[B] = new AbstractIterator[B] {
    val iter    = entriesIterator
    def hasNext = iter.hasNext
    def next()  = iter.next().value
  }

  /** Toggles whether a size map is used to track hash map statistics.
   */
  def useSizeMap(t: Boolean) = if (t) {
    if (!isSizeMapDefined) sizeMapInitAndRebuild()
  } else sizeMapDisable()

  protected def createNewEntry[B1](key: A, value: B1): Entry = {
    new Entry(key, value.asInstanceOf[B])
  }

  private def writeObject(out: java.io.ObjectOutputStream) {
    serializeTo(out, { entry =>
      out.writeObject(entry.key)
      out.writeObject(entry.value)
    })
  }

  private def readObject(in: java.io.ObjectInputStream) {
    init(in, createNewEntry(in.readObject().asInstanceOf[A], in.readObject()))
  }

}

/** $factoryInfo
 *  @define Coll `mutable.HashMap`
 *  @define coll mutable hash map
 */
object HashMap extends MutableMapFactory[HashMap] {
  implicit def canBuildFrom[A, B]: CanBuildFrom[Coll, (A, B), HashMap[A, B]] = new MapCanBuildFrom[A, B]
  def empty[A, B]: HashMap[A, B] = new HashMap[A, B]
}