scala.collection
trait Map

[source: `scala/collection/Map.scala`]

`` `trait` Map[A, +B]
  `extends` PartialFunction[A, B]`with` Collection[(A, B)]

  A map is a collection that maps each key to one or zero values.

  This trait provides a limited interface, only allowing reading of elements. There are two extensions of this trait, in packages `scala.collection.mutable` and `scala.collection.immutable`, which provide functionality for adding new key/value mappings to a map. The trait in the first package is for maps that are modified destructively, whereas the trait in the second package is for immutable maps which create a new map when something is added or removed from them.

Author
  Matthias Zenger
  Martin Odersky
Version
  1.2, 31/12/2006

Direct Known Subclasses:
  Map.Projection, MapProxy, SortedMap, Map, Map

Method Summary
`def` | apply (key : A) : B Retrieve the value which is associated with the given key. This method throws an exception if there is no mapping from the given key to a value.
`def` | contains (key : A) : Boolean Is the given key mapped to a value by this map?
`def` | default (key : A) : B The default value for the map, returned when a key is not found The method implemented here yields an error, but it might be overridden in subclasses.
`override def` | equals (that : Any) : Boolean Compares two maps structurally; i.e. checks if all mappings contained in this map are also contained in the other map, and vice versa.
`def` | filterKeys (p : (A) => Boolean) : Projection[A, B] non-strict filter based on keys only
`abstract def` | get (key : A) : Option[B] Check if this map maps `key` to a value and return the value if it exists.
`def` | getOrElse [B2 >: B](key : A, default : => B2) : B2 Check if this map maps `key` to a value. Return that value if it exists, otherwise return `default`.
`override def` | hashCode : Int A hash method compatible with `equals`
`def` | isDefinedAt (key : A) : Boolean Does this map contain a mapping from the given key to a value?
`override def` | isEmpty : Boolean Is this an empty map?
`def` | keySet : Set[A]
`def` | keys : Iterator[A] Creates an iterator for all keys.
`def` | mapElements [C](f : (B) => C) : Projection[A, C] non-strict map elements using existing key set
`override def` | projection : Projection[A, B] returns a projection that can be used to call non-strict `filter`, `map`, and `flatMap` methods that build projections of the collection.
`abstract def` | size : Int Compute the number of key-to-value mappings.
`protected override def` | stringPrefix : java.lang.String Defines the prefix of this object's `toString` representation.
`override def` | toString : java.lang.String Creates a string representation for this map.
`def` | values : Iterator[B] Creates an iterator for a contained values.

Methods inherited from Collection
toArray

Methods inherited from Iterable
elements (abstract), concat, ++, map, flatMap, filter, partition, takeWhile, dropWhile, take, drop, foreach, forall, exists, find, findIndexOf, indexOf, foldLeft, foldRight, /:, :\, reduceLeft, reduceRight, copyToBuffer, sameElements, toList, toStream, mkString, mkString, mkString, addString, addString, copyToArray, hasDefiniteSize

Methods inherited from PartialFunction
orElse, andThen

Methods inherited from Function1
compose

Methods inherited from AnyRef
getClass, clone, notify, notifyAll, wait, wait, wait, finalize, ==, !=, eq, ne, synchronized

Methods inherited from Any
==, !=, isInstanceOf, asInstanceOf

Method Details

`abstract` `def` size : Int

  Compute the number of key-to-value mappings.

Returns
  the number of mappings

Overrides
  Collection.size

`abstract` `def` get(key : A) : Option[B]

  Check if this map maps `key` to a value and return the value if it exists.

Parameters
  `key -` the key of the mapping of interest
Returns
  the value of the mapping, if it exists

`` `def` getOrElse[B2 >: B](key : A, default : => B2) : B2

  Check if this map maps `key` to a value. Return that value if it exists, otherwise return `default`.

`override` `def` isEmpty : Boolean

  Is this an empty map?

Returns
  `true` iff the map is empty.

`` `def` apply(key : A) : B

  Retrieve the value which is associated with the given key. This method throws an exception if there is no mapping from the given key to a value.

Parameters
  `key -` the key
Returns
  the value associated with the given key.

`` `def` contains(key : A) : Boolean

  Is the given key mapped to a value by this map?

Parameters
  `key -` the key
Returns
  `true` iff there is a mapping for key in this map

`` `def` isDefinedAt(key : A) : Boolean

  Does this map contain a mapping from the given key to a value?

Parameters
  `key -` the key
Returns
  `true` iff there is a mapping for key in this map

Overrides
  PartialFunction.isDefinedAt

`` `def` keys : Iterator[A]

  Creates an iterator for all keys.

Returns
  an iterator over all keys.

`` `def` keySet : Set[A]

Returns
  the keys of this map as a set.

`` `def` values : Iterator[B]

  Creates an iterator for a contained values.

Returns
  an iterator over all values.

`override` `def` equals(that : Any) : Boolean

  Compares two maps structurally; i.e. checks if all mappings contained in this map are also contained in the other map, and vice versa.

Parameters
  `that -` the other map
Returns
  `true` iff both maps contain exactly the same mappings.

`override` `def` hashCode : Int

  A hash method compatible with `equals`

`override` `def` toString : java.lang.String

  Creates a string representation for this map.

Returns
  a string showing all mappings

Overrides
  Collection.toString

`` `def` default(key : A) : B

  The default value for the map, returned when a key is not found The method implemented here yields an error, but it might be overridden in subclasses.

Parameters
  `key -` the given key value
Throws
  Predef.NoSuchElementException -

`override` `def` projection : Projection[A, B]

  returns a projection that can be used to call non-strict `filter`, `map`, and `flatMap` methods that build projections of the collection.

`` `def` filterKeys(p : (A) => Boolean) : Projection[A, B]

  non-strict filter based on keys only

`` `def` mapElements[C](f : (B) => C) : Projection[A, C]

  non-strict map elements using existing key set

`protected override` `def` stringPrefix : java.lang.String

  Defines the prefix of this object's `toString` representation.

Overrides
  Collection.stringPrefix