/* Map.java: interface Map -- An object that maps keys to values
interface Map.Entry -- an Entry in a Map
Copyright (C) 1998, 2001, 2004 Free Software Foundation, Inc.
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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
{
/**
* 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 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)
*/
Object 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)
*/
Object put(Object key, Object 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 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 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.
*/
Object remove(Object key);
/**
* 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 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
{
/**
* Get the key corresponding to this entry.
*
* @return the key
*/
Object getKey();
/**
* Get the value corresponding to this entry. If you already called
* Iterator.remove(), this is undefined.
*
* @return the value
*/
Object 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
*/
Object setValue(Object 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 ? ((HashMap) o).getKey() == null
: getKey().equals(((HashMap) o).getKey()))
&& (getValue() == null ? ((HashMap) o).getValue() == null
: getValue().equals(((HashMap) o).getValue()))</pre>
*
* @param o the object to compare
*
* @return <code>true</code> if it is equal
*/
boolean equals(Object o);
}
}