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From-SVN: r102074
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Tom Tromey
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338
libjava/classpath/java/util/Map.java
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libjava/classpath/java/util/Map.java
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/* Map.java: interface Map -- An object that maps keys to values
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interface Map.Entry -- an Entry in a Map
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Copyright (C) 1998, 2001, 2004, 2005 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util;
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/**
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* An object that maps keys onto values. Keys cannot be duplicated. This
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* interface replaces the obsolete {@link Dictionary} abstract class.
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* <p>
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*
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* The map has three collection views, which are backed by the map
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* (modifications on one show up on the other): a set of keys, a collection
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* of values, and a set of key-value mappings. Some maps have a guaranteed
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* order, but not all do.
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* <p>
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*
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* Note: Be careful about using mutable keys. Behavior is unspecified if
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* a key's comparison behavior is changed after the fact. As a corollary
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* to this rule, don't use a Map as one of its own keys or values, as it makes
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* hashCode and equals have undefined behavior.
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* <p>
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*
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* All maps are recommended to provide a no argument constructor, which builds
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* an empty map, and one that accepts a Map parameter and copies the mappings
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* (usually by putAll), to create an equivalent map. Unfortunately, Java
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* cannot enforce these suggestions.
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* <p>
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*
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* The map may be unmodifiable, in which case unsupported operations will
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* throw an UnsupportedOperationException. Note that some operations may be
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* safe, such as putAll(m) where m is empty, even if the operation would
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* normally fail with a non-empty argument.
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*
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* @author Original author unknown
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* @author Eric Blake (ebb9@email.byu.edu)
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* @see HashMap
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* @see TreeMap
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* @see Hashtable
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* @see SortedMap
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* @see Collection
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* @see Set
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* @since 1.2
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* @status updated to 1.4
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*/
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public interface Map
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{
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/**
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* Remove all entries from this Map (optional operation).
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*
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* @throws UnsupportedOperationException if clear is not supported
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*/
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void clear();
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/**
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* Returns true if this contains a mapping for the given key.
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*
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* @param key the key to search for
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* @return true if the map contains the key
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* @throws ClassCastException if the key is of an inappropriate type
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* @throws NullPointerException if key is <code>null</code> but the map
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* does not permit null keys
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*/
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boolean containsKey(Object key);
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/**
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* Returns true if this contains at least one mapping with the given value.
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* In other words, returns true if a value v exists where
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* <code>(value == null ? v == null : value.equals(v))</code>. This usually
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* requires linear time.
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*
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* @param value the value to search for
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* @return true if the map contains the value
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* @throws ClassCastException if the type of the value is not a valid type
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* for this map.
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* @throws NullPointerException if the value is null and the map doesn't
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* support null values.
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*/
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boolean containsValue(Object value);
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/**
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* Returns a set view of the mappings in this Map. Each element in the
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* set is a Map.Entry. The set is backed by the map, so that changes in
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* one show up in the other. Modifications made while an iterator is
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* in progress cause undefined behavior. If the set supports removal,
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* these methods remove the underlying mapping from the map:
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* <code>Iterator.remove</code>, <code>Set.remove</code>,
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* <code>removeAll</code>, <code>retainAll</code>, and <code>clear</code>.
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* Element addition, via <code>add</code> or <code>addAll</code>, is
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* not supported via this set.
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*
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* @return the set view of all mapping entries
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* @see Map.Entry
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*/
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Set entrySet();
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/**
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* Compares the specified object with this map for equality. Returns
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* <code>true</code> if the other object is a Map with the same mappings,
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* that is,<br>
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* <code>o instanceof Map && entrySet().equals(((Map) o).entrySet();</code>
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* This allows comparison of maps, regardless of implementation.
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*
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* @param o the object to be compared
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* @return true if the object equals this map
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* @see Set#equals(Object)
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*/
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boolean equals(Object o);
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/**
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* Returns the value mapped by the given key. Returns <code>null</code> if
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* there is no mapping. However, in Maps that accept null values, you
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* must rely on <code>containsKey</code> to determine if a mapping exists.
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*
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* @param key the key to look up
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* @return the value associated with the key, or null if key not in map
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* @throws ClassCastException if the key is an inappropriate type
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* @throws NullPointerException if this map does not accept null keys
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* @see #containsKey(Object)
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*/
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Object get(Object key);
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/**
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* Associates the given key to the given value (optional operation). If the
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* map already contains the key, its value is replaced. Be aware that in
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* a map that permits <code>null</code> values, a null return does not
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* always imply that the mapping was created.
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*
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* @param key the key to map
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* @param value the value to be mapped
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* @return the previous value of the key, or null if there was no mapping
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* @throws UnsupportedOperationException if the operation is not supported
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* @throws ClassCastException if the key or value is of the wrong type
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* @throws IllegalArgumentException if something about this key or value
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* prevents it from existing in this map
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* @throws NullPointerException if either the key or the value is null,
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* and the map forbids null keys or values
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* @see #containsKey(Object)
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*/
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Object put(Object key, Object value);
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/**
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* Returns the hash code for this map. This is the sum of all hashcodes
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* for each Map.Entry object in entrySet. This allows comparison of maps,
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* regardless of implementation, and satisfies the contract of
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* Object.hashCode.
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*
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* @return the hash code
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* @see Map.Entry#hashCode()
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*/
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int hashCode();
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/**
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* Returns true if the map contains no mappings.
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*
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* @return true if the map is empty
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*/
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boolean isEmpty();
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/**
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* Returns a set view of the keys in this Map. The set is backed by the
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* map, so that changes in one show up in the other. Modifications made
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* while an iterator is in progress cause undefined behavior. If the set
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* supports removal, these methods remove the underlying mapping from
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* the map: <code>Iterator.remove</code>, <code>Set.remove</code>,
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* <code>removeAll</code>, <code>retainAll</code>, and <code>clear</code>.
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* Element addition, via <code>add</code> or <code>addAll</code>, is
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* not supported via this set.
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*
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* @return the set view of all keys
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*/
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Set keySet();
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/**
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* Copies all entries of the given map to this one (optional operation). If
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* the map already contains a key, its value is replaced.
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*
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* @param m the mapping to load into this map
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* @throws UnsupportedOperationException if the operation is not supported
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* @throws ClassCastException if a key or value is of the wrong type
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* @throws IllegalArgumentException if something about a key or value
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* prevents it from existing in this map
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* @throws NullPointerException if the map forbids null keys or values, or
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* if <code>m</code> is null.
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* @see #put(Object, Object)
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*/
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void putAll(Map m);
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/**
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* Removes the mapping for this key if present (optional operation). If
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* the key is not present, this returns null. Note that maps which permit
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* null values may also return null if the key was removed.
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*
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* @param key the key to remove
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* @return the value the key mapped to, or null if not present.
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* @throws UnsupportedOperationException if deletion is unsupported
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* @throws NullPointerException if the key is null and this map doesn't
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* support null keys.
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* @throws ClassCastException if the type of the key is not a valid type
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* for this map.
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*/
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Object remove(Object key);
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/**
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* Returns the number of key-value mappings in the map. If there are more
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* than Integer.MAX_VALUE mappings, return Integer.MAX_VALUE.
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*
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* @return the number of mappings
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*/
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int size();
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/**
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* Returns a collection (or bag) view of the values in this Map. The
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* collection is backed by the map, so that changes in one show up in
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* the other. Modifications made while an iterator is in progress cause
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* undefined behavior. If the collection supports removal, these methods
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* remove the underlying mapping from the map: <code>Iterator.remove</code>,
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* <code>Collection.remove</code>, <code>removeAll</code>,
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* <code>retainAll</code>, and <code>clear</code>. Element addition, via
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* <code>add</code> or <code>addAll</code>, is not supported via this
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* collection.
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*
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* @return the collection view of all values
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*/
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Collection values();
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/**
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* A map entry (key-value pair). The Map.entrySet() method returns a set
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* view of these objects; there is no other valid way to come across them.
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* These objects are only valid for the duration of an iteration; in other
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* words, if you mess with one after modifying the map, you are asking
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* for undefined behavior.
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*
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* @author Original author unknown
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* @author Eric Blake (ebb9@email.byu.edu)
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* @see Map
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* @see Map#entrySet()
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* @since 1.2
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* @status updated to 1.4
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*/
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interface Entry
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{
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/**
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* Get the key corresponding to this entry.
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*
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* @return the key
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*/
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Object getKey();
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/**
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* Get the value corresponding to this entry. If you already called
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* Iterator.remove(), this is undefined.
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*
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* @return the value
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*/
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Object getValue();
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/**
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* Replaces the value with the specified object (optional operation).
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* This writes through to the map, and is undefined if you already
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* called Iterator.remove().
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*
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* @param value the new value to store
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* @return the old value
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* @throws UnsupportedOperationException if the operation is not supported
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* @throws ClassCastException if the value is of the wrong type
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* @throws IllegalArgumentException if something about the value
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* prevents it from existing in this map
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* @throws NullPointerException if the map forbids null values
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*/
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Object setValue(Object value);
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/**
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* Returns the hash code of the entry. This is defined as the
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* exclusive-or of the hashcodes of the key and value (using 0 for
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* <code>null</code>). In other words, this must be:
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*
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<p><pre>(getKey() == null ? 0 : getKey().hashCode())
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^ (getValue() == null ? 0 : getValue().hashCode())</pre>
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*
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* @return the hash code
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*/
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int hashCode();
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/**
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* Compares the specified object with this entry. Returns true only if
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* the object is a mapping of identical key and value. In other words,
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* this must be:
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*
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<p><pre>(o instanceof Map.Entry)
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&& (getKey() == null ? ((HashMap) o).getKey() == null
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: getKey().equals(((HashMap) o).getKey()))
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&& (getValue() == null ? ((HashMap) o).getValue() == null
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: getValue().equals(((HashMap) o).getValue()))</pre>
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*
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* @param o the object to compare
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*
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* @return <code>true</code> if it is equal
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*/
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boolean equals(Object o);
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}
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}
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