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Java Source | 1999-05-28 | 15.3 KB | 372 lines | [TEXT/CWIE]

/* * @(#)Map.java 1.27 98/09/30 * * Copyright 1997, 1998 by Sun Microsystems, Inc., * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A. * All rights reserved. * * This software is the confidential and proprietary information * of Sun Microsystems, Inc. ("Confidential Information"). You * shall not disclose such Confidential Information and shall use * it only in accordance with the terms of the license agreement * you entered into with Sun. */ package java.util; /** * An object that maps keys to values. A map cannot contain duplicate keys; * each key can map to at most one value. * * This interface takes the place of the <tt>Dictionary</tt> class, which was * a totally abstract class rather than an interface. * * The <tt>Map</tt> interface provides three collection views, which * allow a map's contents to be viewed as a set of keys, collection of values, * or set of key-value mappings. The order of a map is defined as * the order in which the iterators on the map's collection views return their * elements. Some map implementations, like the <tt>TreeMap</tt> class, make * specific guarantees as to their order; others, like the <tt>HashMap</tt> * class, do not. * * Note: great care must be exercised if mutable objects are used as map keys. * The behavior of a map is not specified if the value of an object is changed * in a manner that affects equals comparisons while the object is a * key in the map. A special case of this prohibition is that it is not * permissible for a map to contain itself as a key. While it is permissible * for a map to contain itself as a value, extreme caution is advised: the * equals and hashCode methods are no longer well defined on a such a map. * * All general-purpose map implementation classes should provide two * "standard" constructors: a void (no arguments) constructor which creates an * empty map, and a constructor with a single argument of type <tt>Map</tt>, * which creates a new map with the same key-value mappings as its argument. * In effect, the latter constructor allows the user to copy any map, * producing an equivalent map of the desired class. There is no way to * enforce this recommendation (as interfaces cannot contain constructors) but * all of the general-purpose map implementations in the JDK comply. * * @author Josh Bloch * @version 1.27 09/30/98 * @see HashMap * @see TreeMap * @see Hashtable * @see SortedMap * @see Collection * @see Set * @since JDK1.2 */ public interface Map { // Query Operations /** * Returns the number of key-value mappings in this map. If the * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns * <tt>Integer.MAX_VALUE</tt>. * * @return the number of key-value mappings in this map. */ int size(); /** * Returns <tt>true</tt> if this map contains no key-value mappings. * * @return <tt>true</tt> if this map contains no key-value mappings. */ boolean isEmpty(); /** * Returns <tt>true</tt> if this map contains a mapping for the specified * key. * * @param key key whose presence in this map is to be tested. * @return <tt>true</tt> if this map contains a mapping for the specified * key. * * @throws ClassCastException if the key is of an inappropriate type for * this map. * @throws NullPointerException if the key is <tt>null</tt> and this map * does not not permit <tt>null</tt> keys. */ boolean containsKey(Object key); /** * Returns <tt>true</tt> if this map maps one or more keys to the * specified value. More formally, returns <tt>true</tt> if and only if * this map contains at least one mapping to a value <tt>v</tt> such that * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation * will probably require time linear in the map size for most * implementations of the <tt>Map</tt> interface. * * @param value value whose presence in this map is to be tested. * @return <tt>true</tt> if this map maps one or more keys to the * specified value. */ boolean containsValue(Object value); /** * Returns the value to which this map maps the specified key. Returns * <tt>null</tt> if the map contains no mapping for this key. A return * value of <tt>null</tt> does not necessarily indicate that the * map contains no mapping for the key; it's also possible that the map * explicitly maps the key to <tt>null</tt>. The <tt>containsKey</tt> * operation may be used to distinguish these two cases. * * @param key key whose associated value is to be returned. * @return the value to which this map maps the specified key, or * <tt>null</tt> if the map contains no mapping for this key. * * @throws ClassCastException if the key is of an inappropriate type for * this map. * @throws NullPointerException key is <tt>null</tt> and this map does not * not permit <tt>null</tt> keys. * * @see #containsKey(Object) */ Object get(Object key); // Modification Operations /** * Associates the specified value with the specified key in this map * (optional operation). If the map previously contained a mapping for * this key, the old value is replaced. * * @param key key with which the specified value is to be associated. * @param value value to be associated with the specified key. * @return previous value associated with specified key, or <tt>null</tt> * if there was no mapping for key. A <tt>null</tt> return can * also indicate that the map previously associated <tt>null</tt> * with the specified key, if the implementation supports * <tt>null</tt> values. * * @throws UnsupportedOperationException if the <tt>put</tt> operation is * not supported by this map. * @throws ClassCastException if the class of the specified key or value * prevents it from being stored in this map. * @throws IllegalArgumentException if some aspect of this key or value * prevents it from being stored in this map. * @throws NullPointerException this map does not permit <tt>null</tt> * keys or values, and the specified key or value is * <tt>null</tt>. */ Object put(Object key, Object value); /** * Removes the mapping for this key from this map if present (optional * operation). * * @param key key whose mapping is to be removed from the map. * @return previous value associated with specified key, or <tt>null</tt> * if there was no mapping for key. A <tt>null</tt> return can * also indicate that the map previously associated <tt>null</tt> * with the specified key, if the implementation supports * <tt>null</tt> values. * @throws UnsupportedOperationException if the <tt>remove</tt> method is * not supported by this map. */ Object remove(Object key); // Bulk Operations /** * Copies all of the mappings from the specified map to this map * (optional operation). These mappings will replace any mappings that * this map had for any of the keys currently in the specified map. * * @param t Mappings to be stored in this map. * * @throws UnsupportedOperationException if the <tt>putAll</tt> method is * not supported by this map. * * @throws ClassCastException if the class of a key or value in the * specified map prevents it from being stored in this map. * * @throws IllegalArgumentException some aspect of a key or value in the * specified map prevents it from being stored in this map. * * @throws NullPointerException this map does not permit <tt>null</tt> * keys or values, and the specified key or value is * <tt>null</tt>. */ void putAll(Map t); /** * Removes all mappings from this map (optional operation). * * @throws UnsupportedOperationException clear is not supported by this * map. */ void clear(); // Views /** * Returns a set view of the keys contained in this map. The set is * backed by the map, so changes to the map are reflected in the set, and * vice-versa. If the map is modified while an iteration over the set is * in progress, the results of the iteration are undefined. The set * supports element removal, which removes the corresponding mapping from * the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, * <tt>removeAll</tt> <tt>retainAll</tt>, and <tt>clear</tt> operations. * It does not support the add or <tt>addAll</tt> operations. * * @return a set view of the keys contained in this map. */ public Set keySet(); /** * Returns a collection view of the values contained in this map. The * collection is backed by the map, so changes to the map are reflected in * the collection, and vice-versa. If the map is modified while an * iteration over the collection is in progress, the results of the * iteration are undefined. The collection supports element removal, * which removes the corresponding mapping from the map, via the * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt> operations. * It does not support the add or <tt>addAll</tt> operations. * * @return a collection view of the values contained in this map. */ public Collection values(); /** * Returns a set view of the mappings contained in this map. Each element * in the returned set is a <tt>Map.Entry</tt>. The set is backed by the * map, so changes to the map are reflected in the set, and vice-versa. * If the map is modified while an iteration over the set is in progress, * the results of the iteration are undefined. The set supports element * removal, which removes the corresponding mapping from the map, via the * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>, * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not support * the <tt>add</tt> or <tt>addAll</tt> operations. * * @return a set view of the mappings contained in this map. */ public Set entrySet(); /** * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns * a collection-view of the map, whose elements are of this class. The * only way to obtain a reference to a map entry is from the * iterator of this collection-view. These <tt>Map.Entry</tt> objects are * valid only for the duration of the iteration; more formally, * the behavior of a map entry is undefined if the backing map has been * modified after the entry was returned by the iterator, except through * the iterator's own <tt>remove</tt> operation, or through the * <tt>setValue</tt> operation on a map entry returned by the iterator. * * @see Map#entrySet() */ public interface Entry { /** * Returns the key corresponding to this entry. * * @return the key corresponding to this entry. */ Object getKey(); /** * Returns the value corresponding to this entry. If the mapping * has been removed from the backing map (by the iterator's * <tt>remove</tt> operation), the results of this call are undefined. * * @return the value corresponding to this entry. */ Object getValue(); /** * Replaces the value corresponding to this entry with the specified * value (optional operation). (Writes through to the map.) The * behavior of this call is undefined if the mapping has already been * removed from the map (by the iterator's <tt>remove</tt> operation). * * @param value new value to be stored in this entry. * @return old value corresponding to the entry. * * @throws UnsupportedOperationException if the <tt>put</tt> operation * is not supported by the backing map. * @throws ClassCastException if the class of the specified value * prevents it from being stored in the backing map. * @throws IllegalArgumentException if some aspect of this value * prevents it from being stored in the backing map. * @throws NullPointerException the backing map does not permit * <tt>null</tt> values, and the specified value is * <tt>null</tt>. */ Object setValue(Object value); /** * Compares the specified object with this entry for equality. * Returns <tt>true</tt> if the given object is also a map entry and * the two entries represent the same mapping. More formally, two * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping * if<pre> * (e1.getKey()==null ? * e2.getKey()==null : e1.getKey().equals(e2.getKey())) && * (e1.getValue()==null ? * e2.getValue()==null : e1.getValue().equals(e2.getValue())) * </pre> * This ensures that the <tt>equals</tt> method works properly across * different implementations of the <tt>Map.Entry</tt> interface. * * @param o object to be compared for equality with this map entry. * @return <tt>true</tt> if the specified object is equal to this map * entry. */ boolean equals(Object o); /** * Returns the hash code value for this map entry. The hash code * of a map entry <tt>e</tt> is defined to be: <pre> * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^ * (e.getValue()==null ? 0 : e.getValue().hashCode()) * </pre> * This ensures that <tt>e1.equals(e2)</tt> implies that * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries * <tt>e1</tt> and <tt>e2</tt>, as required by the general * contract of <tt>Object.hashCode</tt>. * * @return the hash code value for this map entry. * @see Object#hashCode() * @see Object#equals(Object) * @see #equals(Object) */ int hashCode(); } // Comparison and hashing /** * Compares the specified object with this map for equality. Returns * <tt>true</tt> if the given object is also a map and the two Maps * represent the same mappings. More formally, two maps <tt>t1</tt> and * <tt>t2</tt> represent the same mappings if * <tt>t1.entrySet().equals(t2.entrySet())</tt>. This ensures that the * <tt>equals</tt> method works properly across different implementations * of the <tt>Map</tt> interface. * * @param o object to be compared for equality with this map. * @return <tt>true</tt> if the specified object is equal to this map. */ boolean equals(Object o); /** * Returns the hash code value for this map. The hash code of a map * is defined to be the sum of the hashCodes of each entry in the map's * entrySet view. This ensures that <tt>t1.equals(t2)</tt> implies * that <tt>t1.hashCode()==t2.hashCode()</tt> for any two maps * <tt>t1</tt> and <tt>t2</tt>, as required by the general * contract of Object.hashCode. * * @return the hash code value for this map. * @see Map.Entry#hashCode() * @see Object#hashCode() * @see Object#equals(Object) * @see #equals(Object) */ int hashCode(); }