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/* Map.java: interface Map -- An object that maps keys to values

             interface Map.Entry -- an Entry in a Map

   Copyright (C) 1998, 2001, 2004, 2005  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

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02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

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permission to link this library with independent modules to produce an

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or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

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exception statement from your version. */

package java.util;

/**

 * An object that maps keys onto values. Keys cannot be duplicated. This

 * interface replaces the obsolete {@link Dictionary} abstract class.

 * <p>

 *

 * The map has three collection views, which are backed by the map

 * (modifications on one show up on the other): a set of keys, a collection

 * of values, and a set of key-value mappings. Some maps have a guaranteed

 * order, but not all do.

 * <p>

 *

 * Note: Be careful about using mutable keys.  Behavior is unspecified if

 * a key's comparison behavior is changed after the fact.  As a corollary

 * to this rule, don't use a Map as one of its own keys or values, as it makes

 * hashCode and equals have undefined behavior.

 * <p>

 *

 * All maps are recommended to provide a no argument constructor, which builds

 * an empty map, and one that accepts a Map parameter and copies the mappings

 * (usually by putAll), to create an equivalent map.  Unfortunately, Java

 * cannot enforce these suggestions.

 * <p>

 *

 * The map may be unmodifiable, in which case unsupported operations will

 * throw an UnsupportedOperationException.  Note that some operations may be

 * safe, such as putAll(m) where m is empty, even if the operation would

 * normally fail with a non-empty argument.

 *

 * @author Original author unknown

 * @author Eric Blake (ebb9@email.byu.edu)

 * @see HashMap

 * @see TreeMap

 * @see Hashtable

 * @see SortedMap

 * @see Collection

 * @see Set

 * @since 1.2

 * @status updated to 1.4

 */

public interface Map<K, V>

{

  /**

   * Remove all entries from this Map (optional operation).

   *

   * @throws UnsupportedOperationException if clear is not supported

   */

  void clear();

  /**

   * Returns true if this contains a mapping for the given key.

   *

   * @param key the key to search for

   * @return true if the map contains the key

   * @throws ClassCastException if the key is of an inappropriate type

   * @throws NullPointerException if key is <code>null</code> but the map

   *         does not permit null keys

   */

  boolean containsKey(Object key);

  /**

   * Returns true if this contains at least one mapping with the given value.

   * In other words, returns true if a value v exists where

   * <code>(value == null ? v == null : value.equals(v))</code>. This usually

   * requires linear time.

   *

   * @param value the value to search for

   * @return true if the map contains the value

   * @throws ClassCastException if the type of the value is not a valid type

   *         for this map.

   * @throws NullPointerException if the value is null and the map doesn't

   *         support null values.

   */

  boolean containsValue(Object value);

  /**

   * Returns a set view of the mappings in this Map.  Each element in the

   * set is a Map.Entry.  The set is backed by the map, so that changes in

   * one show up in the other.  Modifications made while an iterator is

   * in progress cause undefined behavior.  If the set supports removal,

   * these methods remove the underlying mapping from the map:

   * <code>Iterator.remove</code>, <code>Set.remove</code>,

   * <code>removeAll</code>, <code>retainAll</code>, and <code>clear</code>.

   * Element addition, via <code>add</code> or <code>addAll</code>, is

   * not supported via this set.

   *

   * @return the set view of all mapping entries

   * @see Map.Entry

   */

  Set<Map.Entry<K, V>> entrySet();

  /**

   * Compares the specified object with this map for equality. Returns

   * <code>true</code> if the other object is a Map with the same mappings,

   * that is,<br>

   * <code>o instanceof Map && entrySet().equals(((Map) o).entrySet();</code>

   * This allows comparison of maps, regardless of implementation.

   *

   * @param o the object to be compared

   * @return true if the object equals this map

   * @see Set#equals(Object)

   */

  boolean equals(Object o);

  /**

   * Returns the value mapped by the given key. Returns <code>null</code> if

   * there is no mapping.  However, in Maps that accept null values, you

   * must rely on <code>containsKey</code> to determine if a mapping exists.

   *

   * @param key the key to look up

   * @return the value associated with the key, or null if key not in map

   * @throws ClassCastException if the key is an inappropriate type

   * @throws NullPointerException if this map does not accept null keys

   * @see #containsKey(Object)

   */

  V get(Object key);

  /**

   * Associates the given key to the given value (optional operation). If the

   * map already contains the key, its value is replaced. Be aware that in

   * a map that permits <code>null</code> values, a null return does not

   * always imply that the mapping was created.

   *

   * @param key the key to map

   * @param value the value to be mapped

   * @return the previous value of the key, or null if there was no mapping

   * @throws UnsupportedOperationException if the operation is not supported

   * @throws ClassCastException if the key or value is of the wrong type

   * @throws IllegalArgumentException if something about this key or value

   *         prevents it from existing in this map

   * @throws NullPointerException if either the key or the value is null,

   *         and the map forbids null keys or values

   * @see #containsKey(Object)

   */

  V put(K key, V value);

  /**

   * Returns the hash code for this map. This is the sum of all hashcodes

   * for each Map.Entry object in entrySet.  This allows comparison of maps,

   * regardless of implementation, and satisfies the contract of

   * Object.hashCode.

   *

   * @return the hash code

   * @see Map.Entry#hashCode()

   */

  int hashCode();

  /**

   * Returns true if the map contains no mappings.

   *

   * @return true if the map is empty

   */

  boolean isEmpty();

  /**

   * Returns a set view of the keys in this Map.  The set is backed by the

   * map, so that changes in one show up in the other.  Modifications made

   * while an iterator is in progress cause undefined behavior.  If the set

   * supports removal, these methods remove the underlying mapping from

   * the map: <code>Iterator.remove</code>, <code>Set.remove</code>,

   * <code>removeAll</code>, <code>retainAll</code>, and <code>clear</code>.

   * Element addition, via <code>add</code> or <code>addAll</code>, is

   * not supported via this set.

   *

   * @return the set view of all keys

   */

  Set<K> keySet();

  /**

   * Copies all entries of the given map to this one (optional operation). If

   * the map already contains a key, its value is replaced.

   *

   * @param m the mapping to load into this map

   * @throws UnsupportedOperationException if the operation is not supported

   * @throws ClassCastException if a key or value is of the wrong type

   * @throws IllegalArgumentException if something about a key or value

   *         prevents it from existing in this map

   * @throws NullPointerException if the map forbids null keys or values, or

   *         if <code>m</code> is null.

   * @see #put(Object, Object)

   */

  void putAll(Map<? extends K, ? extends V> m);

  /**

   * Removes the mapping for this key if present (optional operation). If

   * the key is not present, this returns null. Note that maps which permit

   * null values may also return null if the key was removed.

   *

   * @param key the key to remove

   * @return the value the key mapped to, or null if not present.

   * @throws UnsupportedOperationException if deletion is unsupported

   * @throws NullPointerException if the key is null and this map doesn't

   *         support null keys.

   * @throws ClassCastException if the type of the key is not a valid type

   *         for this map.

   */

  V remove(Object o);

  /**

   * Returns the number of key-value mappings in the map. If there are more

   * than Integer.MAX_VALUE mappings, return Integer.MAX_VALUE.

   *

   * @return the number of mappings

   */

  int size();

  /**

   * Returns a collection (or bag) view of the values in this Map.  The

   * collection is backed by the map, so that changes in one show up in

   * the other.  Modifications made while an iterator is in progress cause

   * undefined behavior.  If the collection supports removal, these methods

   * remove the underlying mapping from the map: <code>Iterator.remove</code>,

   * <code>Collection.remove</code>, <code>removeAll</code>,

   * <code>retainAll</code>, and <code>clear</code>. Element addition, via

   * <code>add</code> or <code>addAll</code>, is not supported via this

   * collection.

   *

   * @return the collection view of all values

   */

  Collection<V> values();

  /**

   * A map entry (key-value pair). The Map.entrySet() method returns a set

   * view of these objects; there is no other valid way to come across them.

   * These objects are only valid for the duration of an iteration; in other

   * words, if you mess with one after modifying the map, you are asking

   * for undefined behavior.

   *

   * @author Original author unknown

   * @author Eric Blake (ebb9@email.byu.edu)

   * @see Map

   * @see Map#entrySet()

   * @since 1.2

   * @status updated to 1.4

   */

  interface Entry<K, V>

  {

    /**

     * Get the key corresponding to this entry.

     *

     * @return the key

     */

    K getKey();

    /**

     * Get the value corresponding to this entry. If you already called

     * Iterator.remove(), this is undefined.

     *

     * @return the value

     */

    V getValue();

    /**

     * Replaces the value with the specified object (optional operation).

     * This writes through to the map, and is undefined if you already

     * called Iterator.remove().

     *

     * @param value the new value to store

     * @return the old value

     * @throws UnsupportedOperationException if the operation is not supported

     * @throws ClassCastException if the value is of the wrong type

     * @throws IllegalArgumentException if something about the value

     *         prevents it from existing in this map

     * @throws NullPointerException if the map forbids null values

     */

    V setValue(V value);

    /**

     * Returns the hash code of the entry.  This is defined as the

     * exclusive-or of the hashcodes of the key and value (using 0 for

     * <code>null</code>). In other words, this must be:

     *

<p><pre>(getKey() == null ? 0 : getKey().hashCode())

^ (getValue() == null ? 0 : getValue().hashCode())</pre>

     *

     * @return the hash code

     */

    int hashCode();

    /**

     * Compares the specified object with this entry. Returns true only if

     * the object is a mapping of identical key and value. In other words,

     * this must be:

     *

<p><pre>(o instanceof Map.Entry)

&& (getKey() == null ? ((Map.Entry) o).getKey() == null

                     : getKey().equals(((Map.Entry) o).getKey()))

&& (getValue() == null ? ((Map.Entry) o).getValue() == null

                       : getValue().equals(((Map.Entry) o).getValue()))</pre>

     *

     * @param o the object to compare

     *

     * @return <code>true</code> if it is equal

     */

    boolean equals(Object o);

  }

}