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1: /* Map.java: interface Map -- An object that maps keys to values 2: interface Map.Entry -- an Entry in a Map 3: Copyright (C) 1998, 2001, 2004, 2005 Free Software Foundation, Inc. 4: 5: This file is part of GNU Classpath. 6: 7: GNU Classpath is free software; you can redistribute it and/or modify 8: it under the terms of the GNU General Public License as published by 9: the Free Software Foundation; either version 2, or (at your option) 10: any later version. 11: 12: GNU Classpath is distributed in the hope that it will be useful, but 13: WITHOUT ANY WARRANTY; without even the implied warranty of 14: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15: General Public License for more details. 16: 17: You should have received a copy of the GNU General Public License 18: along with GNU Classpath; see the file COPYING. If not, write to the 19: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 20: 02110-1301 USA. 21: 22: Linking this library statically or dynamically with other modules is 23: making a combined work based on this library. Thus, the terms and 24: conditions of the GNU General Public License cover the whole 25: combination. 26: 27: As a special exception, the copyright holders of this library give you 28: permission to link this library with independent modules to produce an 29: executable, regardless of the license terms of these independent 30: modules, and to copy and distribute the resulting executable under 31: terms of your choice, provided that you also meet, for each linked 32: independent module, the terms and conditions of the license of that 33: module. An independent module is a module which is not derived from 34: or based on this library. If you modify this library, you may extend 35: this exception to your version of the library, but you are not 36: obligated to do so. If you do not wish to do so, delete this 37: exception statement from your version. */ 38: 39: 40: package java.util; 41: 42: /** 43: * An object that maps keys onto values. Keys cannot be duplicated. This 44: * interface replaces the obsolete {@link Dictionary} abstract class. 45: * <p> 46: * 47: * The map has three collection views, which are backed by the map 48: * (modifications on one show up on the other): a set of keys, a collection 49: * of values, and a set of key-value mappings. Some maps have a guaranteed 50: * order, but not all do. 51: * <p> 52: * 53: * Note: Be careful about using mutable keys. Behavior is unspecified if 54: * a key's comparison behavior is changed after the fact. As a corollary 55: * to this rule, don't use a Map as one of its own keys or values, as it makes 56: * hashCode and equals have undefined behavior. 57: * <p> 58: * 59: * All maps are recommended to provide a no argument constructor, which builds 60: * an empty map, and one that accepts a Map parameter and copies the mappings 61: * (usually by putAll), to create an equivalent map. Unfortunately, Java 62: * cannot enforce these suggestions. 63: * <p> 64: * 65: * The map may be unmodifiable, in which case unsupported operations will 66: * throw an UnsupportedOperationException. Note that some operations may be 67: * safe, such as putAll(m) where m is empty, even if the operation would 68: * normally fail with a non-empty argument. 69: * 70: * @author Original author unknown 71: * @author Eric Blake (ebb9@email.byu.edu) 72: * @see HashMap 73: * @see TreeMap 74: * @see Hashtable 75: * @see SortedMap 76: * @see Collection 77: * @see Set 78: * @since 1.2 79: * @status updated to 1.4 80: */ 81: public interface Map<K, V> 82: { 83: /** 84: * Remove all entries from this Map (optional operation). 85: * 86: * @throws UnsupportedOperationException if clear is not supported 87: */ 88: void clear(); 89: 90: /** 91: * Returns true if this contains a mapping for the given key. 92: * 93: * @param key the key to search for 94: * @return true if the map contains the key 95: * @throws ClassCastException if the key is of an inappropriate type 96: * @throws NullPointerException if key is <code>null</code> but the map 97: * does not permit null keys 98: */ 99: boolean containsKey(Object key); 100: 101: /** 102: * Returns true if this contains at least one mapping with the given value. 103: * In other words, returns true if a value v exists where 104: * <code>(value == null ? v == null : value.equals(v))</code>. This usually 105: * requires linear time. 106: * 107: * @param value the value to search for 108: * @return true if the map contains the value 109: * @throws ClassCastException if the type of the value is not a valid type 110: * for this map. 111: * @throws NullPointerException if the value is null and the map doesn't 112: * support null values. 113: */ 114: boolean containsValue(Object value); 115: 116: /** 117: * Returns a set view of the mappings in this Map. Each element in the 118: * set is a Map.Entry. The set is backed by the map, so that changes in 119: * one show up in the other. Modifications made while an iterator is 120: * in progress cause undefined behavior. If the set supports removal, 121: * these methods remove the underlying mapping from the map: 122: * <code>Iterator.remove</code>, <code>Set.remove</code>, 123: * <code>removeAll</code>, <code>retainAll</code>, and <code>clear</code>. 124: * Element addition, via <code>add</code> or <code>addAll</code>, is 125: * not supported via this set. 126: * 127: * @return the set view of all mapping entries 128: * @see Map.Entry 129: */ 130: Set<Map.Entry<K, V>> entrySet(); 131: 132: /** 133: * Compares the specified object with this map for equality. Returns 134: * <code>true</code> if the other object is a Map with the same mappings, 135: * that is,<br> 136: * <code>o instanceof Map && entrySet().equals(((Map) o).entrySet();</code> 137: * This allows comparison of maps, regardless of implementation. 138: * 139: * @param o the object to be compared 140: * @return true if the object equals this map 141: * @see Set#equals(Object) 142: */ 143: boolean equals(Object o); 144: 145: /** 146: * Returns the value mapped by the given key. Returns <code>null</code> if 147: * there is no mapping. However, in Maps that accept null values, you 148: * must rely on <code>containsKey</code> to determine if a mapping exists. 149: * 150: * @param key the key to look up 151: * @return the value associated with the key, or null if key not in map 152: * @throws ClassCastException if the key is an inappropriate type 153: * @throws NullPointerException if this map does not accept null keys 154: * @see #containsKey(Object) 155: */ 156: V get(Object key); 157: 158: /** 159: * Associates the given key to the given value (optional operation). If the 160: * map already contains the key, its value is replaced. Be aware that in 161: * a map that permits <code>null</code> values, a null return does not 162: * always imply that the mapping was created. 163: * 164: * @param key the key to map 165: * @param value the value to be mapped 166: * @return the previous value of the key, or null if there was no mapping 167: * @throws UnsupportedOperationException if the operation is not supported 168: * @throws ClassCastException if the key or value is of the wrong type 169: * @throws IllegalArgumentException if something about this key or value 170: * prevents it from existing in this map 171: * @throws NullPointerException if either the key or the value is null, 172: * and the map forbids null keys or values 173: * @see #containsKey(Object) 174: */ 175: V put(K key, V value); 176: 177: /** 178: * Returns the hash code for this map. This is the sum of all hashcodes 179: * for each Map.Entry object in entrySet. This allows comparison of maps, 180: * regardless of implementation, and satisfies the contract of 181: * Object.hashCode. 182: * 183: * @return the hash code 184: * @see Map.Entry#hashCode() 185: */ 186: int hashCode(); 187: 188: /** 189: * Returns true if the map contains no mappings. 190: * 191: * @return true if the map is empty 192: */ 193: boolean isEmpty(); 194: 195: /** 196: * Returns a set view of the keys in this Map. The set is backed by the 197: * map, so that changes in one show up in the other. Modifications made 198: * while an iterator is in progress cause undefined behavior. If the set 199: * supports removal, these methods remove the underlying mapping from 200: * the map: <code>Iterator.remove</code>, <code>Set.remove</code>, 201: * <code>removeAll</code>, <code>retainAll</code>, and <code>clear</code>. 202: * Element addition, via <code>add</code> or <code>addAll</code>, is 203: * not supported via this set. 204: * 205: * @return the set view of all keys 206: */ 207: Set<K> keySet(); 208: 209: /** 210: * Copies all entries of the given map to this one (optional operation). If 211: * the map already contains a key, its value is replaced. 212: * 213: * @param m the mapping to load into this map 214: * @throws UnsupportedOperationException if the operation is not supported 215: * @throws ClassCastException if a key or value is of the wrong type 216: * @throws IllegalArgumentException if something about a key or value 217: * prevents it from existing in this map 218: * @throws NullPointerException if the map forbids null keys or values, or 219: * if <code>m</code> is null. 220: * @see #put(Object, Object) 221: */ 222: void putAll(Map<? extends K, ? extends V> m); 223: 224: /** 225: * Removes the mapping for this key if present (optional operation). If 226: * the key is not present, this returns null. Note that maps which permit 227: * null values may also return null if the key was removed. 228: * 229: * @param key the key to remove 230: * @return the value the key mapped to, or null if not present. 231: * @throws UnsupportedOperationException if deletion is unsupported 232: * @throws NullPointerException if the key is null and this map doesn't 233: * support null keys. 234: * @throws ClassCastException if the type of the key is not a valid type 235: * for this map. 236: */ 237: V remove(Object o); 238: 239: /** 240: * Returns the number of key-value mappings in the map. If there are more 241: * than Integer.MAX_VALUE mappings, return Integer.MAX_VALUE. 242: * 243: * @return the number of mappings 244: */ 245: int size(); 246: 247: /** 248: * Returns a collection (or bag) view of the values in this Map. The 249: * collection is backed by the map, so that changes in one show up in 250: * the other. Modifications made while an iterator is in progress cause 251: * undefined behavior. If the collection supports removal, these methods 252: * remove the underlying mapping from the map: <code>Iterator.remove</code>, 253: * <code>Collection.remove</code>, <code>removeAll</code>, 254: * <code>retainAll</code>, and <code>clear</code>. Element addition, via 255: * <code>add</code> or <code>addAll</code>, is not supported via this 256: * collection. 257: * 258: * @return the collection view of all values 259: */ 260: Collection<V> values(); 261: 262: /** 263: * A map entry (key-value pair). The Map.entrySet() method returns a set 264: * view of these objects; there is no other valid way to come across them. 265: * These objects are only valid for the duration of an iteration; in other 266: * words, if you mess with one after modifying the map, you are asking 267: * for undefined behavior. 268: * 269: * @author Original author unknown 270: * @author Eric Blake (ebb9@email.byu.edu) 271: * @see Map 272: * @see Map#entrySet() 273: * @since 1.2 274: * @status updated to 1.4 275: */ 276: interface Entry<K, V> 277: { 278: /** 279: * Get the key corresponding to this entry. 280: * 281: * @return the key 282: */ 283: K getKey(); 284: 285: /** 286: * Get the value corresponding to this entry. If you already called 287: * Iterator.remove(), this is undefined. 288: * 289: * @return the value 290: */ 291: V getValue(); 292: 293: /** 294: * Replaces the value with the specified object (optional operation). 295: * This writes through to the map, and is undefined if you already 296: * called Iterator.remove(). 297: * 298: * @param value the new value to store 299: * @return the old value 300: * @throws UnsupportedOperationException if the operation is not supported 301: * @throws ClassCastException if the value is of the wrong type 302: * @throws IllegalArgumentException if something about the value 303: * prevents it from existing in this map 304: * @throws NullPointerException if the map forbids null values 305: */ 306: V setValue(V value); 307: 308: 309: /** 310: * Returns the hash code of the entry. This is defined as the 311: * exclusive-or of the hashcodes of the key and value (using 0 for 312: * <code>null</code>). In other words, this must be: 313: * 314: <p><pre>(getKey() == null ? 0 : getKey().hashCode()) 315: ^ (getValue() == null ? 0 : getValue().hashCode())</pre> 316: * 317: * @return the hash code 318: */ 319: int hashCode(); 320: 321: /** 322: * Compares the specified object with this entry. Returns true only if 323: * the object is a mapping of identical key and value. In other words, 324: * this must be: 325: * 326: <p><pre>(o instanceof Map.Entry) 327: && (getKey() == null ? ((Map.Entry) o).getKey() == null 328: : getKey().equals(((Map.Entry) o).getKey())) 329: && (getValue() == null ? ((Map.Entry) o).getValue() == null 330: : getValue().equals(((Map.Entry) o).getValue()))</pre> 331: * 332: * @param o the object to compare 333: * 334: * @return <code>true</code> if it is equal 335: */ 336: boolean equals(Object o); 337: } 338: }