diff options
Diffstat (limited to 'libjava/java/util/Map.java')
| -rw-r--r-- | libjava/java/util/Map.java | 270 |
1 files changed, 265 insertions, 5 deletions
diff --git a/libjava/java/util/Map.java b/libjava/java/util/Map.java index b1d4326..2cd22b3 100644 --- a/libjava/java/util/Map.java +++ b/libjava/java/util/Map.java @@ -1,5 +1,6 @@ -/* Map.java -- An object that maps keys to values - Copyright (C) 1998 Free Software Foundation, Inc. +/* Map.java: interface Map -- An object that maps keys to values + interface Map.Entry -- an Entry in a Map + Copyright (C) 1998, 2001 Free Software Foundation, Inc. This file is part of GNU Classpath. @@ -25,34 +26,293 @@ This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. */ -// TO DO: -// ~ Doc comments for everything. - 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 + */ public 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 + */ public 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 + */ public 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 + */ public 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) + */ public 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) + */ public 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 the map forbids null keys or values + * @see #containsKey(Object) + */ public 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() + */ public int hashCode(); + + /** + * Returns true if the map contains no mappings. + * + * @return true if the map is empty + */ public 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 + */ public 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) + */ public 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 + */ public Object 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 + */ public 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 + */ public 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 + */ public static interface Entry { + /** + * Get the key corresponding to this entry. + * + * @return the key + */ public Object getKey(); + + /** + * Get the value corresponding to this entry. If you already called + * Iterator.remove(), this is undefined. + * + * @return the value + */ public 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 + */ public 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 null). In other + * words, this must be: + * <pre> + * (getKey() == null ? 0 : getKey().hashCode()) ^ + * (getValue() == null ? 0 : getValue().hashCode()) + * </pre> + * + * @return the hash code + */ public 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: + * <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 true if it is equal + */ public boolean equals(Object o); } } |