´ó²¿·ÖJava¿ª·¢Õß¶¼ÔÚʹÓÃMap£¬ÌرðÊÇHashMap¡£HashMapÊÇÒ»ÖÖ¼òµ¥µ«Ç¿´óµÄ·½Ê½È¥´æ´¢ºÍ»ñÈ¡Êý¾Ý¡£µ«ÓжàÉÙ¿ª·¢ÕßÖªµÀ
HashMapÄÚ²¿ÈçºÎ¹¤×÷ÄØ£¿¼¸Ììǰ£¬ÎÒÔĶÁÁËjava.util.HashMapµÄ´óÁ¿Ô´´úÂ루°üÀ¨Java
7 ºÍJava 8£©£¬À´ÉîÈëÀí½âÕâ¸ö»ù´¡µÄÊý¾Ý½á¹¹¡£ÔÚÕâÆªÎÄÕÂÖУ¬ÎÒ»á½âÊÍjava.util.HashMapµÄʵÏÖ£¬ÃèÊöJava
8ʵÏÖÖÐÌí¼ÓµÄÐÂÌØÐÔ£¬²¢ÌÖÂÛÐÔÄÜ¡¢ÄÚ´æÒÔ¼°Ê¹ÓÃHashMapʱµÄһЩÒÑÖªÎÊÌâ¡£
ÄÚ²¿´æ´¢
Java HashMapÀàʵÏÖÁËMap<K, V>½Ó¿Ú¡£Õâ¸ö½Ó¿ÚÖеÄÖ÷Òª·½·¨°üÀ¨£º V put(K key, V value) V get(Object key) V remove(Object key) Boolean containsKey(Object key) |
HashMapʹÓÃÁËÒ»¸öÄÚ²¿ÀàEntry<K, V>À´´æ´¢Êý¾Ý¡£Õâ¸öÄÚ²¿ÀàÊÇÒ»¸ö¼òµ¥µÄ¼üÖµ¶Ô£¬²¢´øÓжîÍâÁ½¸öÊý¾Ý£º
Ò»¸öÖ¸ÏòÆäËûÈë¿Ú£¨ÒëÕß×¢£ºÒýÓöÔÏ󣩵ÄÒýÓã¬ÕâÑùHashMap¿ÉÒÔ´æ´¢ÀàËÆÁ´½ÓÁбíÕâÑùµÄ¶ÔÏó¡£
Ò»¸öÓÃÀ´´ú±í¼üµÄ¹þÏ£Öµ£¬´æ´¢Õâ¸öÖµ¿ÉÒÔ±ÜÃâHashMapÔÚÿ´ÎÐèҪʱ¶¼ÖØÐÂÉú³É¼üËù¶ÔÓ¦µÄ¹þÏ£Öµ¡£
ÏÂÃæÊÇEntry<K, V>ÔÚJava 7ϵÄÒ»²¿·Ö´úÂ룺
static class Entry<K,V> implements Map.Entry<K,V> { final K key; V value; Entry<K,V> next; int hash; ¡ } |
HashMap½«Êý¾Ý´æ´¢µ½¶à¸öµ¥ÏòEntryÁ´±íÖУ¨ÓÐʱҲ±»³ÆÎªÍ°bucket»òÕßÈÝÆ÷orbins£©¡£ËùÓеÄÁÐ±í¶¼±»×¢²áµ½Ò»¸öEntryÊý×éÖУ¨Entry<K,
V>[]Êý×飩£¬Õâ¸öÄÚ²¿Êý×éµÄĬÈϳ¤¶ÈÊÇ16¡£
ÏÂÃæÕâ·ùͼÃèÊöÁËÒ»¸öHashMapʵÀýµÄÄÚ²¿´æ´¢£¬Ëü°üº¬Ò»¸önullable¶ÔÏó×é³ÉµÄÊý×顣ÿ¸ö¶ÔÏó¶¼Á¬½Óµ½ÁíÍâÒ»¸ö¶ÔÏó£¬ÕâÑù¾Í¹¹³ÉÁËÒ»¸öÁ´±í¡£

ËùÓоßÓÐÏàͬ¹þÏ£ÖµµÄ¼ü¶¼»á±»·Åµ½Í¬Ò»¸öÁ´±í£¨Í°£©ÖС£¾ßÓв»Í¬¹þÏ£ÖµµÄ¼ü×îÖÕ¿ÉÄÜ»áÔÚÏàͬµÄͰÖС£
µ±Óû§µ÷Óà put(K key£¬ V value) »òÕß get(Object key) ʱ£¬³ÌÐò»á¼ÆËã¶ÔÏóÓ¦¸ÃÔÚµÄͰµÄË÷Òý¡£È»ºó£¬³ÌÐò»áµü´ú±éÀú¶ÔÓ¦µÄÁÐ±í£¬À´Ñ°ÕÒ¾ßÓÐÏàͬ¼üµÄEntry¶ÔÏó£¨Ê¹ÓüüµÄequals()·½·¨£©¡£
¶ÔÓÚµ÷ÓÃget()µÄÇé¿ö£¬³ÌÐò»á·µ»ØÖµËù¶ÔÓ¦µÄEntry¶ÔÏó£¨Èç¹ûEntry¶ÔÏó´æÔÚ£©¡£
¶ÔÓÚµ÷ÓÃput(K key, V value)µÄÇé¿ö£¬Èç¹ûEntry¶ÔÏóÒѾ´æÔÚ£¬ÄÇô³ÌÐò»á½«ÖµÌ滻ΪÐÂÖµ£¬·ñÔò£¬³ÌÐò»áÔÚµ¥ÏòÁ´±íµÄ±íÍ·´´½¨Ò»¸öеÄEntry£¨´Ó²ÎÊýÖеļüºÍÖµ£©¡£
Ͱ£¨Á´±í£©µÄË÷Òý£¬ÊÇͨ¹ýmapµÄ3¸ö²½ÖèÉú³ÉµÄ£º
Ê×ÏÈ»ñÈ¡¼üµÄÉ¢ÁÐÂë¡£
³ÌÐòÖØ¸´É¢ÁÐÂ룬À´×èÖ¹Õë¶Ô¼üµÄÔã¸âµÄ¹þÏ£º¯Êý£¬ÒòΪÕâÓпÉÄܻὫËùÓеÄÊý¾Ý¶¼·Åµ½ÄÚ²¿Êý×éµÄÏàͬµÄË÷Òý£¨Í°£©ÉÏ¡£
³ÌÐòÄõ½Öظ´ºóµÄÉ¢ÁÐÂ룬²¢¶ÔÆäʹÓÃÊý×鳤¶È£¨×îСÊÇ1£©µÄλÑÚÂ루bit-mask£©¡£Õâ¸ö²Ù×÷¿ÉÒÔ±£Ö¤Ë÷Òý²»»á´óÓÚÊý×éµÄ´óС¡£Äã¿ÉÒÔ½«Æä¿´×öÊÇÒ»¸ö¾¹ý¼ÆËãµÄÓÅ»¯È¡Ä£º¯Êý¡£
ÏÂÃæÊÇÉú³ÉË÷ÒýµÄÔ´´úÂ룺
// the "rehash" function in JAVA 7 that takes the hashcode of the key static int hash(int h) { h ^= (h >>> 20) ^ (h >>> 12); return h ^ (h >>> 7) ^ (h >>> 4); } // the "rehash" function in JAVA 8 that directly takes the key static final int hash(Object key) { int h; return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16); } // the function that returns the index from the rehashed hash static int indexFor(int h, int length) { return h & (length-1); } |
ΪÁ˸üÓÐЧµØ¹¤×÷£¬ÄÚ²¿Êý×éµÄ´óС±ØÐëÊÇ2µÄÃÝÖµ¡£ÈÃÎÒÃÇ¿´Ò»ÏÂΪʲô£º
¼ÙÉèÊý×éµÄ³¤¶ÈÊÇ17£¬ÄÇôÑÚÂëµÄÖµ¾ÍÊÇ16£¨Êý×鳤¶È-1£©¡£16µÄ¶þ½øÖƱíʾÊÇ0¡010000£¬ÕâÑù¶ÔÓÚÈκÎÖµHÀ´Ëµ£¬¡°H
& 16¡±µÄ½á¹û¾ÍÊÇ16»òÕß0¡£ÕâÒâζ×ų¤¶ÈΪ17µÄÊý×éÖ»ÄÜÓ¦Óõ½Á½¸öͰÉÏ£ºÒ»¸öÊÇ0£¬ÁíÍâÒ»¸öÊÇ16£¬ÕâÑù²»ÊǺÜÓÐЧÂÊ¡£µ«ÊÇÈç¹ûÄ㽫Êý×éµÄ³¤¶ÈÉèÖÃΪ
2µÄÃÝÖµ£¬ÀýÈç16£¬ÄÇô°´Î»Ë÷ÒýµÄ¹¤×÷±ä³É¡°H & 15¡±¡£15µÄ¶þ½øÖƱíʾÊÇ0¡001111£¬Ë÷Òý¹«Ê½Êä³öµÄÖµ¿ÉÒÔ´Ó0µ½15£¬ÕâÑù³¤¶ÈΪ16µÄÊý×é¾Í¿ÉÒÔ±»³ä·ÖʹÓÃÁË¡£ÀýÈ磺
Èç¹ûH = 952£¬ËüµÄ¶þ½øÖƱíʾÊÇ0..01110111000£¬¶ÔÓ¦µÄË÷ÒýÊÇ0¡01000 = 8
Èç¹ûH = 1576£¬ËüµÄ¶þ½øÖƱíʾÊÇ0..011000101000£¬¶ÔÓ¦µÄË÷ÒýÊÇ0¡01000 =
8
Èç¹ûH = 12356146£¬ËüµÄ¶þ½øÖƱíʾÊÇ0..0101111001000101000110010£¬¶ÔÓ¦µÄË÷ÒýÊÇ0¡00010
= 2
Èç¹ûH = 59843£¬ËüµÄ¶þ½øÖƱíʾÊÇ0..01110100111000011£¬Ëü¶ÔÓ¦µÄË÷ÒýÊÇ0¡00011
= 3
ÕâÖÖ»úÖÆ¶ÔÓÚ¿ª·¢ÕßÀ´ËµÊÇ͸Ã÷µÄ£ºÈç¹ûËûÑ¡ÔñÒ»¸ö³¤¶ÈΪ37µÄHashMap£¬Map»á×Ô¶¯Ñ¡ÔñÏÂÒ»¸ö´óÓÚ37µÄ2µÄÃÝÖµ£¨64£©×÷ΪÄÚ²¿Êý×éµÄ³¤¶È¡£
×Ô¶¯µ÷Õû´óС
ÔÚ»ñÈ¡Ë÷Òýºó£¬get()¡¢put()»òÕßremove()·½·¨»á·ÃÎʶÔÓ¦µÄÁ´±í£¬À´²é¿´Õë¶ÔÖ¸¶¨¼üµÄEntry¶ÔÏóÊÇ·ñÒѾ´æÔÚ¡£ÔÚ²»×öÐ޸ĵÄÇé
¿öÏ£¬Õâ¸ö»úÖÆ¿ÉÄܻᵼÖÂÐÔÄÜÎÊÌ⣬ÒòΪÕâ¸ö·½·¨ÐèÒªµü´úÕû¸öÁбíÀ´²é¿´Entry¶ÔÏóÊÇ·ñ´æÔÚ¡£¼ÙÉèÄÚ²¿Êý×éµÄ³¤¶È²ÉÓÃĬÈÏÖµ16£¬¶øÄãÐèÒª´æ´¢
2£¬000,000Ìõ¼Ç¼¡£ÔÚ×îºÃµÄÇé¿öÏ£¬Ã¿¸öÁ´±í»áÓÐ125,000¸öEntry¶ÔÏó£¨2,000,000/16£©¡£get()¡¢remove()ºÍ
put()·½·¨ÔÚÿһ´ÎÖ´ÐÐʱ£¬¶¼ÐèÒª½øÐÐ125,000´Îµü´ú¡£ÎªÁ˱ÜÃâÕâÖÖÇé¿ö£¬HashMap¿ÉÒÔÔö¼ÓÄÚ²¿Êý×éµÄ³¤¶È£¬´Ó¶ø±£Ö¤Á´±íÖÐÖ»±£ÁôºÜÉÙµÄ
Entry¶ÔÏó¡£
µ±Äã´´½¨Ò»¸öHashMapʱ£¬Äã¿ÉÒÔͨ¹ýÒÔϹ¹Ô캯ÊýÖ¸¶¨Ò»¸ö³õʼ³¤¶È£¬ÒÔ¼°Ò»¸öloadFactor£º
public HashMap(int initialCapacity, float loadFactor) |
Èç¹ûÄã²»Ö¸¶¨²ÎÊý£¬ÄÇôĬÈϵÄinitialCapacityµÄÖµÊÇ16£¬ loadFactorµÄĬÈÏÖµÊÇ0.75¡£initialCapacity´ú±íÄÚ²¿Êý×éµÄÁ´±íµÄ³¤¶È¡£
µ±Äãÿ´ÎʹÓÃput(¡)·½·¨ÏòMapÖÐÌí¼ÓÒ»¸öеļüÖµ¶Ôʱ£¬¸Ã·½·¨»á¼ì²éÊÇ·ñÐèÒªÔö¼ÓÄÚ²¿Êý×éµÄ³¤¶È¡£ÎªÁËʵÏÖÕâÒ»µã£¬Map´æ´¢ÁË2¸öÊý¾Ý£º
MapµÄ´óС£ºËü´ú±íHashMapÖмǼµÄÌõÊý¡£ÎÒÃÇÔÚÏòHashMapÖвåÈë»òÕßɾ³ýֵʱ¸üÐÂËü¡£
·§Öµ£ºËüµÈÓÚÄÚ²¿Êý×éµÄ³¤¶È*loadFactor£¬ÔÚÿ´Îµ÷ÕûÄÚ²¿Êý×éµÄ³¤¶Èʱ£¬¸Ã·§ÖµÒ²»áͬʱ¸üС£
ÔÚÌí¼ÓеÄEntry¶ÔÏó֮ǰ£¬put(¡)·½·¨»á¼ì²éµ±Ç°MapµÄ´óСÊÇ·ñ´óÓÚ·§Öµ¡£Èç¹û´óÓÚ·§Öµ£¬Ëü»á´´½¨Ò»¸öеÄÊý×飬Êý×鳤¶ÈÊǵ±Ç°ÄÚ²¿Êý
×éµÄÁ½±¶¡£ÒòΪÐÂÊý×éµÄ´óСÒѾ·¢Éú¸Ä±ä£¬ËùÒÔË÷Òýº¯Êý£¨¾ÍÊÇ·µ»Ø¡°¼üµÄ¹þÏ£Öµ & (Êý×鳤¶È-1)¡±µÄλÔËËã½á¹û£©Ò²ËæÖ®¸Ä±ä¡£µ÷ÕûÊý×éµÄ´óС»á´´½¨Á½¸öеÄͰ£¨Á´±í£©£¬²¢ÇÒ½«ËùÓÐÏÖ´æEntry¶ÔÏóÖØÐ·ÖÅ䵽ͰÉÏ¡£µ÷ÕûÊý×é´óСµÄÄ¿
±êÔÚÓÚ½µµÍÁ´±íµÄ´óС£¬´Ó¶ø½µµÍput()¡¢remove()ºÍget()·½·¨µÄÖ´ÐÐʱ¼ä¡£¶ÔÓÚ¾ßÓÐÏàͬ¹þÏ£ÖµµÄ¼üËù¶ÔÓ¦µÄËùÓÐEntry¶ÔÏóÀ´Ëµ£¬ËüÃÇ
»áÔÚµ÷Õû´óСºó·ÖÅäµ½ÏàͬµÄͰÖС£µ«ÊÇ£¬Èç¹ûÁ½¸öEntry¶ÔÏóµÄ¼üµÄ¹þÏ£Öµ²»Ò»Ñù£¬µ«ËüÃÇ֮ǰÔÚͬһ¸öͰÉÏ£¬ÄÇôÔÚµ÷ÕûÒԺ󣬲¢²»Äܱ£Ö¤ËüÃÇÒÀÈ»ÔÚͬһ
¸öͰÉÏ¡£

Õâ·ùͼƬÃèÊöÁ˵÷ÕûǰºÍµ÷ÕûºóµÄÄÚ²¿Êý×éµÄÇé¿ö¡£ÔÚµ÷ÕûÊý×鳤¶È֮ǰ£¬ÎªÁ˵õ½Entry¶ÔÏóE£¬MapÐèÒªµü´ú±éÀúÒ»¸ö°üº¬5¸öÔªËØµÄÁ´±í¡£ÔÚµ÷
ÕûÊý×鳤¶ÈÖ®ºó£¬Í¬ÑùµÄget()·½·¨ÔòÖ»ÐèÒª±éÀúÒ»¸ö°üº¬2¸öÔªËØµÄÁ´±í£¬ÕâÑùget()·½·¨ÔÚµ÷ÕûÊý×鳤¶ÈºóµÄÔËÐÐËÙ¶ÈÌá¸ßÁË2±¶¡£
Ḭ̈߳²È«
Èç¹ûÄãÒѾ·Ç³£ÊìϤHashMap£¬ÄÇôÄã¿Ï¶¨ÖªµÀËü²»ÊÇḬ̈߳²È«µÄ£¬µ«ÊÇÎªÊ²Ã´ÄØ£¿ÀýÈç¼ÙÉèÄãÓÐÒ»¸öWriterỊ̈߳¬ËüÖ»»áÏòMapÖвåÈëÒѾ´æÔÚµÄÊý¾Ý£¬Ò»¸öReaderỊ̈߳¬Ëü»á´ÓMapÖжÁÈ¡Êý¾Ý£¬ÄÇôËüΪʲô²»¹¤×÷ÄØ£¿
ÒòΪÔÚ×Ô¶¯µ÷Õû´óСµÄ»úÖÆÏ£¬Èç¹ûÏß³ÌÊÔ×ÅÈ¥Ìí¼Ó»òÕß»ñȡһ¸ö¶ÔÏó£¬Map¿ÉÄÜ»áʹÓþɵÄË÷ÒýÖµ£¬ÕâÑù¾Í²»»áÕÒµ½Entry¶ÔÏóËùÔÚµÄÐÂͰ¡£
ÔÚ×îÔã¸âµÄÇé¿öÏ£¬µ±2¸öÏß³Ìͬʱ²åÈëÊý¾Ý£¬¶ø2´Îput()µ÷Óûáͬʱ³ö·¢Êý×é×Ô¶¯µ÷Õû´óС¡£¼ÈÈ»Á½¸öÏß³ÌÔÚͬʱÐÞ¸ÄÁ´±í£¬ÄÇôMapÓпÉÄÜÔÚÒ»¸öÁ´±íµÄÄÚ²¿Ñ»·ÖÐÍ˳ö¡£Èç¹ûÄãÊÔ×ÅÈ¥»ñȡһ¸ö´øÓÐÄÚ²¿Ñ»·µÄÁбíÖеÄÊý¾Ý£¬ÄÇôget()·½·¨ÓÀÔ¶²»»á½áÊø¡£
HashTableÌṩÁËÒ»¸öḬ̈߳²È«µÄʵÏÖ£¬¿ÉÒÔ×èÖ¹ÉÏÊöÇé¿ö·¢Éú¡£µ«ÊÇ£¬¼ÈÈ»ËùÓеÄͬ²½µÄCRUD²Ù×÷¶¼·Ç³£Âý¡£ÀýÈ磬Èç¹ûÏß³Ì1µ÷ÓÃ
get(key1)£¬È»ºóÏß³Ì2µ÷ÓÃget(key2)£¬Ïß³Ì2µ÷ÓÃget(key3)£¬ÄÇôÔÚÖ¸¶¨Ê±¼ä£¬Ö»ÄÜÓÐ1¸öÏ߳̿ÉÒԵõ½ËüµÄÖµ£¬µ«ÊÇ3¸öÏ̶߳¼
¿ÉÒÔͬʱ·ÃÎÊÕâЩÊý¾Ý¡£
´ÓJava 5¿ªÊ¼£¬ÎÒÃǾÍÓµÓÐÒ»¸ö¸üºÃµÄ¡¢±£Ö¤Ḭ̈߳²È«µÄHashMapʵÏÖ£ºConcurrentHashMap¡£¶ÔÓÚConcurrentMapÀ´Ëµ£¬Ö»ÓÐͰÊÇ
ͬ²½µÄ£¬ÕâÑùÈç¹û¶à¸öÏ̲߳»Ê¹ÓÃͬһ¸öͰ»òÕßµ÷ÕûÄÚ²¿Êý×éµÄ´óС£¬ËüÃÇ¿ÉÒÔͬʱµ÷ÓÃget()¡¢remove()»òÕßput()·½·¨¡£ÔÚÒ»¸ö¶àÏß³ÌÓ¦ÓóÌ
ÐòÖУ¬ÕâÖÖ·½Ê½ÊǸüºÃµÄÑ¡Ôñ¡£
¼üµÄ²»±äÐÔ
Ϊʲô½«×Ö·û´®ºÍÕûÊý×÷ΪHashMapµÄ¼üÊÇÒ»ÖֺܺõÄʵÏÖ£¿Ö÷ÒªÊÇÒòΪËüÃÇÊDz»¿É±äµÄ£¡Èç¹ûÄãÑ¡Ôñ×Ô¼º´´½¨Ò»¸öÀà×÷Ϊ¼ü£¬µ«²»Äܱ£Ö¤Õâ¸öÀàÊDz»¿É±äµÄ£¬ÄÇôÄã¿ÉÄÜ»áÔÚHashMapÄÚ²¿¶ªÊ§Êý¾Ý¡£
ÎÒÃÇÀ´¿´ÏÂÃæµÄÓÃÀý£º
ÄãÓÐÒ»¸ö¼ü£¬ËüµÄÄÚ²¿ÖµÊÇ¡°1¡±¡£
ÄãÏòHashMapÖвåÈëÒ»¸ö¶ÔÏó£¬ËüµÄ¼ü¾ÍÊÇ¡°1¡±¡£
HashMap´Ó¼ü£¨¼´¡°1¡±£©µÄÉ¢ÁÐÂëÖÐÉú³É¹þÏ£Öµ¡£
MapÔÚд´½¨µÄ¼Ç¼Öд洢Õâ¸ö¹þÏ£Öµ¡£
Äã¸Ä¶¯¼üµÄÄÚ²¿Öµ£¬½«Æä±äΪ¡°2¡±¡£
¼üµÄ¹þÏ£Öµ·¢ÉúÁ˸ı䣬µ«ÊÇHashMap²¢²»ÖªµÀÕâÒ»µã£¨ÒòΪ´æ´¢µÄÊǾɵĹþÏ£Öµ£©¡£
ÄãÊÔ×Åͨ¹ýÐ޸ĺóµÄ¼ü»ñÈ¡ÏàÓ¦µÄ¶ÔÏó¡£
Map»á¼ÆËãеļü£¨¼´¡°2¡±£©µÄ¹þÏ£Öµ£¬´Ó¶øÕÒµ½Entry¶ÔÏóËùÔÚµÄÁ´±í£¨Í°£©¡£
Çé¿ö1£º ¼ÈÈ»ÄãÒѾÐÞ¸ÄÁ˼ü£¬Map»áÊÔ×ÅÔÚ´íÎóµÄͰÖÐѰÕÒEntry¶ÔÏó£¬Ã»ÓÐÕÒµ½¡£
Çé¿ö2£º ÄãºÜÐÒÔË£¬Ð޸ĺóµÄ¼üÉú³ÉµÄͰºÍ¾É¼üÉú³ÉµÄͰÊÇͬһ¸ö¡£MapÕâʱ»áÔÚÁ´±íÖнøÐбéÀú£¬ÒÑÕÒµ½¾ßÓÐÏàͬ¼üµÄEntry¶ÔÏó¡£µ«ÊÇΪÁËѰÕÒ¼ü£¬MapÊ×ÏÈ»á
ͨ¹ýµ÷ÓÃequals()·½·¨À´±È½Ï¼üµÄ¹þÏ£Öµ¡£ÒòΪÐ޸ĺóµÄ¼ü»áÉú³É²»Í¬µÄ¹þÏ£Öµ£¨¾ÉµÄ¹þÏ£Öµ±»´æ´¢ÔڼǼÖУ©£¬ÄÇôMapûÓа취ÔÚÁ´±íÖÐÕÒµ½¶ÔÓ¦µÄ
Entry¶ÔÏó¡£
ÏÂÃæÊÇÒ»¸öJavaʾÀý£¬ÎÒÃÇÏòMapÖвåÈëÁ½¸ö¼üÖµ¶Ô£¬È»ºóÎÒÐ޸ĵÚÒ»¸ö¼ü£¬²¢ÊÔ×ÅÈ¥»ñÈ¡ÕâÁ½¸ö¶ÔÏó¡£Äã»á·¢ÏÖ´ÓMapÖзµ»ØµÄÖ»Óеڶþ¸ö¶ÔÏ󣬵ÚÒ»¸ö¶ÔÏóÒѾ¡°¶ªÊ§¡±ÔÚHashMapÖУº
public class MutableKeyTest { public static void main(String[] args) { class MyKey { Integer i; public void setI(Integer i) { this.i = i; } public MyKey(Integer i) { this.i = i; } @Override public int hashCode() { return i; } @Override public boolean equals(Object obj) { if (obj instanceof MyKey) { return i.equals(((MyKey) obj).i); } else return false; } } Map<MyKey, String> myMap = new HashMap<>(); MyKey key1 = new MyKey(1); MyKey key2 = new MyKey(2); myMap.put(key1, "test " + 1); myMap.put(key2, "test " + 2); // modifying key1 key1.setI(3); String test1 = myMap.get(key1); String test2 = myMap.get(key2); System.out.println("test1= " + test1 + " test2=" + test2); } } |
ÉÏÊö´úÂëµÄÊä³öÊÇ¡°test1=null test2=test 2¡±¡£ÈçÎÒÃÇÆÚÍûµÄÄÇÑù£¬MapûÓÐÄÜÁ¦»ñÈ¡¾¹ýÐ޸ĵļü
1Ëù¶ÔÓ¦µÄ×Ö·û´®1¡£
Java 8 ÖеĸĽø
ÔÚJava 8ÖУ¬HashMapÖеÄÄÚ²¿ÊµÏÖ½øÐÐÁ˺ܶàÐ޸ġ£µÄÈ·Èç´Ë£¬Java 7ʹÓÃÁË1000ÐдúÂëÀ´ÊµÏÖ£¬¶øJava
8ÖÐʹÓÃÁË2000ÐдúÂë¡£ÎÒÔÚÇ°ÃæÃèÊöµÄ´ó²¿·ÖÄÚÈÝÔÚJava 8ÖÐÒÀÈ»ÊǶԵ쬳ýÁËʹÓÃÁ´±íÀ´±£´æEntry¶ÔÏó¡£ÔÚJava
8ÖУ¬ÎÒÃÇÈÔȻʹÓÃÊý×飬µ«Ëü»á±»±£´æÔÚNodeÖУ¬NodeÖаüº¬Á˺Í֮ǰEntry¶ÔÏóÒ»ÑùµÄÐÅÏ¢£¬²¢ÇÒÒ²»áʹÓÃÁ´±í£º
ÏÂÃæÊÇÔÚJava 8ÖÐNodeʵÏÖµÄÒ»²¿·Ö´úÂ룺
static class Node<K,V> implements Map.Entry<K,V> { final int hash; final K key; V value; Node<K,V> next; |
ÄÇôºÍJava 7Ïà±È£¬µ½µ×ÓÐʲô´óµÄÇø±ðÄØ£¿ºÃ°É£¬Node¿ÉÒÔ±»À©Õ¹³ÉTreeNode¡£TreeNodeÊÇÒ»¸öºìºÚÊ÷µÄÊý¾Ý½á¹¹£¬Ëü¿ÉÒÔ´æ´¢¸ü¶àµÄÐÅÏ¢£¬ÕâÑùÎÒÃÇ
¿ÉÒÔÔÚO(log(n))µÄ¸´ÔÓ¶ÈÏÂÌí¼Ó¡¢É¾³ý»òÕß»ñȡһ¸öÔªËØ¡£ÏÂÃæµÄʾÀýÃèÊöÁËTreeNode±£´æµÄËùÓÐÐÅÏ¢£º
static final class TreeNode<K,V> extends LinkedHashMap.Entry<K,V> { final int hash; // inherited from Node<K,V> final K key; // inherited from Node<K,V> V value; // inherited from Node<K,V> Node<K,V> next; // inherited from Node<K,V> Entry<K,V> before, after;// inherited from LinkedHashMap.Entry<K,V> TreeNode<K,V> parent; TreeNode<K,V> left; TreeNode<K,V> right; TreeNode<K,V> prev; boolean red; |
ºìºÚÊ÷ÊÇ×ÔÆ½ºâµÄ¶þ²æËÑË÷Ê÷¡£ËüµÄÄÚ²¿»úÖÆ¿ÉÒÔ±£Ö¤ËüµÄ³¤¶È×ÜÊÇlog(n)£¬²»¹ÜÎÒÃÇÊÇÌí¼Ó»¹ÊÇɾ³ý½Úµã¡£Ê¹ÓÃÕâÖÖÀàÐ͵ÄÊ÷£¬×îÖ÷ÒªµÄºÃ´¦ÊÇÕë¶Ô
ÄÚ²¿±íÖÐÐí¶àÊý¾Ý¶¼¾ßÓÐÏàͬË÷Òý£¨Í°£©µÄÇé¿ö£¬Õâʱ¶ÔÊ÷½øÐÐËÑË÷µÄ¸´ÔÓ¶ÈÊÇO(log(n))£¬¶ø¶ÔÓÚÁ´±íÀ´Ëµ£¬Ö´ÐÐÏàͬµÄ²Ù×÷£¬¸´ÔÓ¶ÈÊÇO(n)¡£
ÈçÄãËù¼û£¬ÎÒÃÇÔÚÊ÷ÖÐȷʵ´æ´¢Á˱ÈÁ´±í¸ü¶àµÄÊý¾Ý¡£¸ù¾Ý¼Ì³ÐÔÔò£¬ÄÚ²¿±íÖпÉÒÔ°üº¬Node£¨Á´±í£©»òÕßTreeNode£¨ºìºÚÊ÷£©¡£Oracle¾ö¶¨¸ù¾ÝÏÂÃæµÄ¹æÔòÀ´Ê¹ÓÃÕâÁ½ÖÖÊý¾Ý½á¹¹£º
- ¶ÔÓÚÄÚ²¿±íÖеÄÖ¸¶¨Ë÷Òý£¨Í°£©£¬Èç¹ûnodeµÄÊýÄ¿¶àÓÚ8¸ö£¬ÄÇôÁ´±í¾Í»á±»×ª»»³ÉºìºÚÊ÷¡£
- ¶ÔÓÚÄÚ²¿±íÖеÄÖ¸¶¨Ë÷Òý£¨Í°£©£¬Èç¹ûnodeµÄÊýĿСÓÚ6¸ö£¬ÄÇôºìºÚÊ÷¾Í»á±»×ª»»³ÉÁ´±í¡£

ÕâÕÅͼƬÃèÊöÁËÔÚJava 8 HashMapÖеÄÄÚ²¿Êý×飬Ëü¼È°üº¬Ê÷£¨Í°0£©£¬Ò²°üº¬Á´±í£¨Í°1£¬2ºÍ3£©¡£Í°0ÊÇÒ»¸öÊ÷½á¹¹ÊÇÒòΪËü°üº¬µÄ½Úµã´óÓÚ8¸ö¡£
Äڴ濪Ïú
JAVA 7
ʹÓÃHashMap»áÏûºÄһЩÄÚ´æ¡£ÔÚJava 7ÖУ¬HashMap½«¼üÖµ¶Ô·â×°³ÉEntry¶ÔÏó£¬Ò»¸öEntry¶ÔÏó°üº¬ÒÔÏÂÐÅÏ¢£º
Ö¸ÏòÏÂÒ»¸ö¼Ç¼µÄÒýÓÃ
Ò»¸öÔ¤ÏȼÆËãµÄ¹þÏ£Öµ£¨ÕûÊý£©
Ò»¸öÖ¸Ïò¼üµÄÒýÓÃ
Ò»¸öÖ¸ÏòÖµµÄÒýÓÃ
´ËÍ⣬Java 7ÖеÄHashMapʹÓÃÁËEntry¶ÔÏóµÄÄÚ²¿Êý×é¡£¼ÙÉèÒ»¸öJava
7 HashMap°üº¬N¸öÔªËØ£¬ËüµÄÄÚ²¿Êý×éµÄÈÝÁ¿ÊÇCAPACITY£¬ÄÇô¶îÍâµÄÄÚ´æÏûºÄ´óÔ¼ÊÇ£º
sizeOf(integer)* N + sizeOf(reference)* (3*N+C) |
ÆäÖУº
ÕûÊýµÄ´óСÊÇ4¸ö×Ö½Ú
ÒýÓõĴóСÒÀÀµÓÚJVM¡¢²Ù×÷ϵͳÒÔ¼°´¦ÀíÆ÷£¬µ«Í¨³£¶¼ÊÇ4¸ö×Ö½Ú¡£
Õâ¾ÍÒâζ×ÅÄÚ´æ×Ü¿ªÏúͨ³£ÊÇ16 * N + 4 * CAPACITY×Ö½Ú¡£
×¢Ò⣺ÔÚMap×Ô¶¯µ÷Õû´óСºó£¬CAPACITYµÄÖµÊÇÏÂÒ»¸ö´óÓÚNµÄ×îСµÄ2µÄÃÝÖµ¡£
×¢Ò⣺´ÓJava 7¿ªÊ¼£¬HashMap²ÉÓÃÁËÑÓ³Ù¼ÓÔØµÄ»úÖÆ¡£ÕâÒâζ׿´Ê¹ÄãΪHashMapÖ¸¶¨ÁË´óС£¬ÔÚÎÒÃǵÚÒ»´ÎʹÓÃput()·½·¨Ö®Ç°£¬¼Ç¼ʹÓõÄÄÚ²¿Êý×飨ºÄ·Ñ4*CAPACITY×Ö½Ú£©Ò²²»»áÔÚÄÚ´æÖзÖÅä¿Õ¼ä¡£
JAVA 8
ÔÚJava 8ʵÏÖÖУ¬¼ÆËãÄÚ´æÊ¹ÓÃÇé¿ö±äµÃ¸´ÔÓһЩ£¬ÒòΪNode¿ÉÄÜ»áºÍEntry´æ´¢ÏàͬµÄÊý¾Ý£¬»òÕßÔÚ´Ë»ù´¡ÉÏÔÙÔö¼Ó6¸öÒýÓúÍÒ»¸öBooleanÊôÐÔ£¨Ö¸¶¨ÊÇ·ñÊÇTreeNode£©¡£
Èç¹ûËùÓеĽڵ㶼ֻÊÇNode£¬ÄÇôJava 8 HashMapÏûºÄµÄÄÚ´æºÍJava 7 HashMapÏûºÄµÄÄÚ´æÊÇÒ»ÑùµÄ¡£
Èç¹ûËùÓеĽڵ㶼ÊÇTreeNode£¬ÄÇôJava 8 HashMapÏûºÄµÄÄÚ´æ¾Í±ä³É£º
N * sizeOf(integer) + N * sizeOf(boolean) + sizeOf(reference)* (9*N+CAPACITY ) |
Ôڴ󲿷ֱê×¼JVMÖУ¬ÉÏÊö¹«Ê½µÄ½á¹ûÊÇ44 * N + 4 * CAPACITY ×Ö½Ú¡£
ÐÔÄÜÎÊÌâ
·Ç¶Ô³ÆHashMap vs ¾ùºâHashMap
ÔÚ×îºÃµÄÇé¿öÏ£¬get()ºÍput()·½·¨¶¼Ö»ÓÐO(1)µÄ¸´ÔÓ¶È¡£µ«ÊÇ£¬Èç¹ûÄ㲻ȥ¹ØÐļüµÄ¹þÏ£º¯Êý£¬ÄÇôÄãµÄput()ºÍget()·½·¨¿ÉÄÜ
»áÖ´Ðзdz£Âý¡£put()ºÍget()·½·¨µÄ¸ßЧִÐУ¬È¡¾öÓÚÊý¾Ý±»·ÖÅäµ½ÄÚ²¿Êý×飨Ͱ£©µÄ²»Í¬µÄË÷ÒýÉÏ¡£Èç¹û¼üµÄ¹þÏ£º¯ÊýÉè¼Æ²»ºÏÀí£¬Äã»áµÃµ½Ò»¸ö·Ç¶Ô
³ÆµÄ·ÖÇø£¨²»¹ÜÄÚ²¿Êý¾ÝµÄÊǶà´ó£©¡£ËùÓеÄput()ºÍget()·½·¨»áʹÓÃ×î´óµÄÁ´±í£¬ÕâÑù¾Í»áÖ´ÐкÜÂý£¬ÒòΪËüÐèÒªµü´úÁ´±íÖеÄÈ«²¿¼Ç¼¡£ÔÚ×µÄÇé
¿öÏ£¨Èç¹û´ó²¿·ÖÊý¾Ý¶¼ÔÚͬһ¸öͰÉÏ£©£¬ÄÇôÄãµÄʱ¼ä¸´ÔӶȾͻá±äΪO(n)¡£
ÏÂÃæÊÇÒ»¸ö¿ÉÊÓ»¯µÄʾÀý¡£µÚÒ»ÕÅͼÃèÊöÁËÒ»¸ö·Ç¶Ô³ÆHashMap£¬µÚ¶þÕÅͼÃèÊöÁËÒ»¸ö¾ùºâHashMap¡£

ÔÚÕâ¸ö·Ç¶Ô³ÆHashMapÖУ¬ÔÚͰ0ÉÏÔËÐÐget()ºÍput()·½·¨»áºÜ»¨·Ñʱ¼ä¡£»ñÈ¡¼Ç¼KÐèÒª»¨·Ñ6´Îµü´ú¡£

ÔÚÕâ¸ö¾ùºâHashMapÖУ¬»ñÈ¡¼Ç¼KÖ»ÐèÒª»¨·Ñ3´Îµü´ú¡£ÕâÁ½¸öHashMap´æ´¢ÁËÏàͬÊýÁ¿µÄÊý¾Ý£¬²¢ÇÒÄÚ²¿Êý×éµÄ´óСһÑù¡£Î¨Ò»µÄÇø±ðÊǼüµÄ¹þÏ£º¯Êý£¬Õâ¸öº¯ÊýÓÃÀ´½«¼Ç¼·Ö²¼µ½²»Í¬µÄͰÉÏ¡£
ÏÂÃæÊÇÒ»¸öʹÓÃJava±àдµÄ¼«¶ËʾÀý£¬ÔÚÕâ¸öʾÀýÖУ¬ÎÒʹÓùþÏ£º¯Êý½«ËùÓеÄÊý¾Ý·Åµ½ÏàͬµÄÁ´±í£¨Í°£©£¬È»ºóÎÒÌí¼ÓÁË2,000,000ÌõÊý¾Ý¡£
public class Test { public static void main(String[] args) { class MyKey { Integer i; public MyKey(Integer i){ this.i =i; } @Override public int hashCode() { return 1; } @Override public boolean equals(Object obj) { ¡ } } Date begin = new Date(); Map <MyKey,String> myMap= new HashMap<>(2_500_000,1); for (int i=0;i<2_000_000;i++){ myMap.put( new MyKey(i), "test "+i); } Date end = new Date(); System.out.println("Duration (ms) "+ (end.getTime()-begin.getTime())); } } |
ÎҵĻúÆ÷ÅäÖÃÊÇcore i5-2500k @ 3.6G£¬ÔÚjava 8u40ÏÂÐèÒª»¨·Ñ³¬¹ý45·ÖÖÓµÄʱ¼äÀ´ÔËÐУ¨ÎÒÔÚ45·ÖÖÓºóÍ£Ö¹Á˽ø³Ì£©¡£Èç¹ûÎÒÔËÐÐͬÑùµÄ´úÂ룬
µ«ÊÇÎÒʹÓÃÈçϵÄhashº¯Êý£º
@Override public int hashCode() { int key = 2097152-1; return key+2097152*i; } |
ÔËÐÐËüÐèÒª»¨·Ñ46Ã룬ºÍ֮ǰ±È£¬ÕâÖÖ·½Ê½ºÃºÜ¶àÁË£¡ÐµÄhashº¯Êý±È¾ÉµÄhashº¯ÊýÔÚ´¦Àí¹þÏ£·ÖÇøÊ±¸üºÏÀí£¬Òò´Ëµ÷ÓÃput()·½·¨»á¸ü¿ìһЩ¡£Èç¹ûÄãÏÖÔÚÔËÐÐÏàͬµÄ´úÂ룬µ«ÊÇʹÓÃÏÂÃæµÄhashº¯Êý£¬ËüÌṩÁ˸üºÃµÄ¹þÏ£·ÖÇø£º
@Override public int hashCode() { return i; } |
ÏÖÔÚÖ»ÐèÒª»¨·Ñ2Ã룡
ÎÒÏ£ÍûÄãÄܹ»Òâʶµ½¹þÏ£º¯ÊýÓжàÖØÒª¡£Èç¹ûÔÚJava 7ÉÏÃæÔËÐÐͬÑùµÄ²âÊÔ£¬µÚÒ»¸öºÍµÚ¶þ¸öµÄÇé¿ö»á¸üÔ㣨ÒòΪJava
7ÖеÄput()·½·¨¸´ÔÓ¶ÈÊÇO(n)£¬¶øJava 8Öеĸ´ÔÓ¶ÈÊÇO(log(n))¡£
ÔÚʹÓÃHashMapʱ£¬ÄãÐèÒªÕë¶Ô¼üÕÒµ½Ò»ÖÖ¹þÏ£º¯Êý£¬¿ÉÒÔ½«¼üÀ©É¢µ½×î¿ÉÄܵÄͰÉÏ¡£Îª´Ë£¬ÄãÐèÒª±ÜÃâ¹þÏ£³åÍ»¡£String¶ÔÏóÊÇÒ»¸ö·Ç³£ºÃµÄ¼ü£¬ÒòΪËüÓкܺõĹþÏ£º¯Êý¡£IntegerÒ²ºÜºÃ£¬ÒòΪËüµÄ¹þÏ£Öµ¾ÍÊÇËü×ÔÉíµÄÖµ¡£
µ÷Õû´óСµÄ¿ªÏú
Èç¹ûÄãÐèÒª´æ´¢´óÁ¿Êý¾Ý£¬ÄãÓ¦¸ÃÔÚ´´½¨HashMapʱָ¶¨Ò»¸ö³õʼµÄÈÝÁ¿£¬Õâ¸öÈÝÁ¿Ó¦¸Ã½Ó½üÄãÆÚÍûµÄ´óС¡£
Èç¹ûÄã²»ÕâÑù×ö£¬Map»áʹÓÃĬÈϵĴóС£¬¼´16£¬factorLoadµÄÖµÊÇ0.75¡£Ç°11´Îµ÷ÓÃput()·½·¨»á·Ç³£¿ì£¬µ«ÊǵÚ12´Î
£¨16*0.75£©µ÷ÓÃʱ»á´´½¨Ò»¸öеij¤¶ÈΪ32µÄÄÚ²¿Êý×飨ÒÔ¼°¶ÔÓ¦µÄÁ´±í/Ê÷£©£¬µÚ13´Îµ½µÚ22´Îµ÷ÓÃput()·½·¨»áºÜ¿ì£¬µ«ÊǵÚ23´Î
£¨32*0.75£©µ÷ÓÃʱ»áÖØÐ´´½¨£¨ÔÙÒ»´Î£©Ò»¸öеÄÄÚ²¿Êý×飬Êý×éµÄ³¤¶È·±¶¡£È»ºóÄÚ²¿µ÷Õû´óСµÄ²Ù×÷»áÔÚµÚ48´Î¡¢96´Î¡¢192´Î¡..µ÷ÓÃ
put()·½·¨Ê±´¥·¢¡£Èç¹ûÊý¾ÝÁ¿²»´ó£¬Öؽ¨ÄÚ²¿Êý×éµÄ²Ù×÷»áºÜ¿ì£¬µ«ÊÇÊý¾ÝÁ¿ºÜ´óʱ£¬»¨·ÑµÄʱ¼ä¿ÉÄÜ»á´ÓÃë¼¶µ½·ÖÖÓ¼¶¡£Í¨¹ý³õʼ»¯Ê±Ö¸¶¨MapÆÚÍûµÄ´ó
С£¬Äã¿ÉÒÔ±ÜÃâµ÷Õû´óС²Ù×÷´øÀ´µÄÏûºÄ¡£
µ«ÕâÀïÒ²ÓÐÒ»¸öȱµã£ºÈç¹ûÄ㽫Êý×éÉèÖõķdz£´ó£¬ÀýÈç2^28£¬µ«ÄãÖ»ÊÇÓÃÁËÊý×éÖеÄ2^26¸öͰ£¬ÄÇôÄ㽫»áÀË·Ñ´óÁ¿µÄÄڴ棨ÔÚÕâ¸öʾÀýÖдóÔ¼ÊÇ2^30×Ö½Ú£©¡£
½áÂÛ
¶ÔÓÚ¼òµ¥µÄÓÃÀý£¬ÄãûÓбØÒªÖªµÀHashMapÊÇÈçºÎ¹¤×÷µÄ£¬ÒòΪÄã²»»á¿´µ½O(1)¡¢O(n)ÒÔ¼°O(log(n))Ö®¼äµÄÇø±ð¡£µ«ÊÇÈç¹ûÄܹ»Àí½âÕâÒ»¾³£Ê¹ÓõÄÊý¾Ý½á¹¹±³ºóµÄ»úÖÆ£¬×ÜÊÇÓкô¦µÄ¡£ÁíÍ⣬¶ÔÓÚJava¿ª·¢ÕßְλÀ´Ëµ£¬ÕâÊÇÒ»µÀµäÐ͵ÄÃæÊÔÎÊÌâ¡£
¶ÔÓÚ´óÊý¾ÝÁ¿µÄÇé¿ö£¬Á˽âHashMapÈçºÎ¹¤×÷ÒÔ¼°Àí½â¼üµÄ¹þÏ£º¯ÊýµÄÖØÒªÐԾͱäµÃ·Ç³£ÖØÒª¡£
ÎÒÏ£ÍûÕâÆªÎÄÕ¿ÉÒÔ°ïÖúÄã¶ÔHashMapµÄʵÏÖÓÐÒ»¸öÉîÈëµÄÀí½â¡£
|