http://www.iteye.com/topic/257191
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浠婂ぉ涓嬪崍鐮旂┒浜嗗崐澶﹉ashcode()鍜宔quals()鏂規(guī)硶錛岀粓浜庢湁浜嗕竴鐐圭偣鐨勬槑鐧斤紝鍐欎笅鏉ヤ笌澶у鍒嗕韓錛坺haoxudong 2008.10.23鏅?1.36錛夈?
1. 棣栧厛equals()鍜宧ashcode()榪欎袱涓柟娉曢兘鏄粠object綾諱腑緇ф壙榪囨潵鐨勩?
equals()鏂規(guī)硶鍦╫bject綾諱腑瀹氫箟濡備笅錛?
public boolean equals(Object obj) {
return (this == obj);
}
寰堟槑鏄炬槸瀵逛袱涓璞$殑鍦板潃鍊艱繘琛岀殑姣旇緝錛堝嵆姣旇緝寮曠敤鏄惁鐩稿悓錛夈備絾鏄垜浠繀闇娓呮錛屽綋String 銆丮ath銆佽繕鏈塈nteger銆丏ouble銆傘傘傘傜瓑榪欎簺灝佽綾誨湪浣跨敤equals()鏂規(guī)硶鏃訛紝宸茬粡瑕嗙洊浜唎bject綾葷殑equals錛堬級鏂規(guī)硶銆傛瘮 濡傚湪String綾諱腑濡備笅錛?
public boolean equals(Object anObject) {
if (this == anObject) {
return true;
}
if (anObject instanceof String) {
String anotherString = (String)anObject;
int n = count;
if (n == anotherString.count) {
char v1[] = value;
char v2[] = anotherString.value;
int i = offset;
int j = anotherString.offset;
while (n-- != 0) {
if (v1[i++] != v2[j++])
return false;
}
return true;
}
}
return false;
}
寰堟槑鏄撅紝榪欐槸榪涜鐨勫唴瀹規(guī)瘮杈冿紝鑰屽凡緇忎笉鍐嶆槸鍦板潃鐨勬瘮杈冦備緷嬈$被鎺―ouble銆両nteger銆丮ath銆傘傘傘傜瓑絳夎繖浜涚被閮芥槸閲嶅啓浜唀quals()鏂規(guī)硶鐨勶紝浠庤岃繘琛岀殑鏄唴瀹圭殑姣旇緝銆傚綋鐒朵簡鍩烘湰綾誨瀷鏄繘琛屽肩殑姣旇緝錛岃繖涓病鏈変粈涔堝ソ璇寸殑銆?
鎴戜滑榪樺簲璇ユ敞鎰忥紝Java璇█瀵筫quals()鐨勮姹傚涓嬶紝榪欎簺瑕佹眰鏄繀欏婚伒寰殑錛?
• 瀵圭О鎬э細濡傛灉x.equals(y)榪斿洖鏄?#8220;true”錛岄偅涔坹.equals(x)涔熷簲璇ヨ繑鍥炴槸“true”銆?
• 鍙嶅皠鎬э細x.equals(x)蹇呴』榪斿洖鏄?#8220;true”銆?
• 綾繪帹鎬э細濡傛灉x.equals(y)榪斿洖鏄?#8220;true”錛岃屼笖y.equals(z)榪斿洖鏄?#8220;true”錛岄偅涔坺.equals(x)涔熷簲璇ヨ繑鍥炴槸“true”銆?
• 榪樻湁涓鑷存э細濡傛灉x.equals(y)榪斿洖鏄?#8220;true”錛屽彧瑕亁鍜寉鍐呭涓鐩翠笉鍙橈紝涓嶇浣犻噸澶峹.equals(y)澶氬皯嬈★紝榪斿洖閮芥槸“true”銆?
• 浠諱綍鎯呭喌涓嬶紝x.equals(null)錛屾案榪滆繑鍥炴槸“false”錛泋.equals(鍜寈涓嶅悓綾誨瀷鐨勫璞?姘歌繙榪斿洖鏄?#8220;false”銆?
浠ヤ笂榪欎簲鐐規(guī)槸閲嶅啓equals()鏂規(guī)硶鏃訛紝蹇呴』閬靛畧鐨勫噯鍒欙紝濡傛灉榪濆弽浼氬嚭鐜版剰鎯充笉鍒扮殑緇撴灉錛岃澶у涓瀹氳閬靛畧銆?
2. 鍏舵鏄痟ashcode() 鏂規(guī)硶錛屽湪object綾諱腑瀹氫箟濡備笅錛?
public native int hashCode();
璇存槑鏄竴涓湰鍦版柟娉曪紝瀹冪殑瀹炵幇鏄牴鎹湰鍦版満鍣ㄧ浉鍏崇殑銆傚綋鐒舵垜浠彲浠ュ湪鑷繁鍐欑殑綾諱腑瑕嗙洊hashcode()鏂規(guī)硶錛屾瘮濡係tring銆?Integer銆丏ouble銆傘傘傘傜瓑絳夎繖浜涚被閮芥槸瑕嗙洊浜唄ashcode()鏂規(guī)硶鐨勩備緥濡傚湪String綾諱腑瀹氫箟鐨刪ashcode()鏂規(guī)硶濡備笅錛?
public int hashCode() {
int h = hash;
if (h == 0) {
int off = offset;
char val[] = value;
int len = count;
for (int i = 0; i < len; i++) {
h = 31*h + val[off++];
}
hash = h;
}
return h;
}
瑙i噴涓涓嬭繖涓▼搴忥紙String鐨凙PI涓啓鍒幫級錛?
s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
浣跨敤 int 綆楁硶錛岃繖閲?s[i] 鏄瓧絎︿覆鐨勭 i 涓瓧絎︼紝n 鏄瓧絎︿覆鐨勯暱搴︼紝^ 琛ㄧず姹傚箓銆傦紙絀哄瓧絎︿覆鐨勫搱甯岀爜涓?0銆傦級
3.榪欓噷鎴戜滑棣栧厛瑕佹槑鐧戒竴涓棶棰橈細
equals()鐩哥瓑鐨勪袱涓璞★紝hashcode()涓瀹氱浉絳夛紱
equals錛堬級涓嶇浉絳夌殑涓や釜瀵硅薄錛屽嵈騫朵笉鑳借瘉鏄庝粬浠殑hashcode()涓嶇浉絳夈傛崲鍙ヨ瘽璇達紝equals()鏂規(guī)硶涓嶇浉絳夌殑涓や釜瀵硅薄錛宧ashcode()鏈夊彲鑳界浉絳夈傦紙鎴戠殑鐞嗚В鏄敱浜庡搱甯岀爜鍦ㄧ敓鎴愮殑鏃跺欎駭鐢熷啿紿侀犳垚鐨勶級銆?
鍙嶈繃鏉ワ細hashcode()涓嶇瓑錛屼竴瀹氳兘鎺ㄥ嚭equals()涔熶笉絳夛紱hashcode()鐩哥瓑錛宔quals()鍙兘鐩哥瓑錛屼篃鍙兘涓嶇瓑銆傝В閲?涓嬬3鐐圭殑浣跨敤鑼冨洿錛屾垜鐨勭悊瑙f槸鍦╫bject銆丼tring絳夌被涓兘鑳戒嬌鐢ㄣ傚湪object綾諱腑錛宧ashcode()鏂規(guī)硶鏄湰鍦版柟娉曪紝榪斿洖鐨勬槸瀵硅薄鐨?鍦板潃鍊鹼紝鑰宱bject綾諱腑鐨別quals()鏂規(guī)硶姣旇緝鐨勪篃鏄袱涓璞$殑鍦板潃鍊鹼紝濡傛灉equals()鐩哥瓑錛岃鏄庝袱涓璞″湴鍧鍊間篃鐩哥瓑錛屽綋鐒?hashcode()涔熷氨鐩哥瓑浜嗭紱鍦⊿tring綾諱腑錛宔quals()榪斿洖鐨勬槸涓や釜瀵硅薄鍐呭鐨勬瘮杈冿紝褰撲袱涓璞″唴瀹圭浉絳夋椂錛?
Hashcode()鏂規(guī)硶鏍規(guī)嵁String綾葷殑閲嶅啓錛堢2鐐歸噷闈㈠凡緇忓垎鏋愪簡錛変唬鐮佺殑鍒嗘瀽錛屼篃鍙煡閬揾ashcode()榪斿洖緇撴灉涔熶細鐩哥瓑銆備互姝ょ被 鎺紝鍙互鐭ラ亾Integer銆丏ouble絳夊皝瑁呯被涓粡榪囬噸鍐欑殑equals()鍜宧ashcode()鏂規(guī)硶涔熷悓鏍烽傚悎浜庤繖涓師鍒欍傚綋鐒舵病鏈夌粡榪囬噸鍐欑殑 綾伙紝鍦ㄧ戶鎵夸簡object綾葷殑equals()鍜宧ashcode()鏂規(guī)硶鍚庯紝涔熶細閬靛畧榪欎釜鍘熷垯銆?
4.璋堝埌hashcode()鍜宔quals()灝變笉鑳戒笉璇村埌hashset,hashmap,hashtable涓殑浣跨敤錛屽叿浣撴槸鎬庢牱鍛紝璇風湅濡備笅鍒嗘瀽錛?
Hashset鏄戶鎵縎et鎺ュ彛錛孲et鎺ュ彛鍙堝疄鐜癈ollection鎺ュ彛錛岃繖鏄眰嬈″叧緋匯傞偅涔坔ashset鏄牴鎹粈涔堝師鐞嗘潵瀛樺彇瀵硅薄鐨勫憿錛?
鍦╤ashset涓笉鍏佽鍑虹幇閲嶅瀵硅薄錛屽厓绱犵殑浣嶇疆涔熸槸涓嶇‘瀹氱殑銆傚湪hashset涓張鏄庢牱鍒ゅ畾鍏冪礌鏄惁閲嶅鐨勫憿錛熻繖灝辨槸闂鐨勫叧閿墍鍦紝緇忚繃涓涓嬪崍鐨勬煡璇㈡眰璇佺粓浜庤幏寰椾簡涓鐐瑰惎紺猴紝鍜屽ぇ瀹跺垎浜竴涓嬶紝鍦╦ava鐨勯泦鍚堜腑錛屽垽鏂袱涓璞℃槸鍚︾浉絳夌殑瑙勫垯鏄細
1)錛屽垽鏂袱涓璞$殑hashCode鏄惁鐩哥瓑
濡傛灉涓嶇浉絳夛紝璁や負涓や釜瀵硅薄涔熶笉鐩哥瓑錛屽畬姣?
濡傛灉鐩哥瓑錛岃漿鍏?)
錛堣繖涓鐐瑰彧鏄負浜嗘彁楂樺瓨鍌ㄦ晥鐜囪岃姹傜殑錛屽叾瀹炵悊璁轟笂娌℃湁涔熷彲浠ワ紝浣嗗鏋滄病鏈夛紝瀹為檯浣跨敤鏃舵晥鐜囦細澶уぇ闄嶄綆錛屾墍浠ユ垜浠繖閲屽皢鍏跺仛涓哄繀闇鐨勩傚悗闈細閲嶇偣璁插埌榪欎釜闂銆傦級
2)錛屽垽鏂袱涓璞$敤equals榪愮畻鏄惁鐩哥瓑
濡傛灉涓嶇浉絳夛紝璁や負涓や釜瀵硅薄涔熶笉鐩哥瓑
濡傛灉鐩哥瓑錛岃涓轟袱涓璞$浉絳夛紙equals()鏄垽鏂袱涓璞℃槸鍚︾浉絳夌殑鍏抽敭錛?
涓轟粈涔堟槸涓ゆ潯鍑嗗垯錛岄毦閬撶敤絎竴鏉′笉琛屽悧錛熶笉琛岋紝鍥犱負鍓嶉潰宸茬粡璇翠簡錛宧ashcode()鐩哥瓑鏃訛紝equals()鏂規(guī)硶涔熷彲鑳戒笉絳夛紝鎵浠ュ繀欏葷敤絎?鏉″噯鍒欒繘琛岄檺鍒訛紝鎵嶈兘淇濊瘉鍔犲叆鐨勪負闈為噸澶嶅厓绱犮?
姣斿涓嬮潰鐨勪唬鐮侊細
public static void main(String args[]){
String s1=new String("zhaoxudong");
String s2=new String("zhaoxudong");
System.out.println(s1==s2);//false
System.out.println(s1.equals(s2));//true
System.out.println(s1.hashCode());//s1.hashcode()絳変簬s2.hashcode()
System.out.println(s2.hashCode());
Set hashset=new HashSet();
hashset.add(s1);
hashset.add(s2);
/*瀹炶川涓婂湪娣誨姞s1,s2鏃訛紝榪愮敤涓婇潰璇村埌鐨勪袱鐐瑰噯鍒欙紝鍙互鐭ラ亾hashset璁や負s1鍜宻2鏄浉絳夌殑錛屾槸鍦ㄦ坊鍔犻噸澶嶅厓绱狅紝鎵浠ヨs2瑕嗙洊浜唖1;*/
Iterator it=hashset.iterator();
while(it.hasNext())
{
System.out.println(it.next());
}
鏈鍚庡湪while寰幆鐨勬椂鍊欏彧鎵撳嵃鍑轟簡涓涓?#8221;zhaoxudong”銆?
杈撳嚭緇撴灉涓猴細false
true
-967303459
-967303459
榪欐槸鍥犱負String綾誨凡緇忛噸鍐欎簡equals()鏂規(guī)硶鍜宧ashcode()鏂規(guī)硶錛屾墍浠ュ湪鏍規(guī)嵁涓婇潰鐨勭1.2鏉″師鍒欏垽瀹氭椂錛宧ashset璁や負瀹冧滑鏄浉絳夌殑瀵硅薄錛岃繘琛屼簡閲嶅娣誨姞銆?
浣嗘槸鐪嬩笅闈㈢殑紼嬪簭錛?
import java.util.*;
public class HashSetTest
{
public static void main(String[] args)
{
HashSet hs=new HashSet();
hs.add(new Student(1,"zhangsan"));
hs.add(new Student(2,"lisi"));
hs.add(new Student(3,"wangwu"));
hs.add(new Student(1,"zhangsan"));
Iterator it=hs.iterator();
while(it.hasNext())
{
System.out.println(it.next());
}
}
}
class Student
{
int num;
String name;
Student(int num,String name)
{
this.num=num;
this.name=name;
}
public String toString()
{
return num+":"+name;
}
}
杈撳嚭緇撴灉涓猴細
1:zhangsan
1:zhangsan
3:wangwu
2:lisi
闂鍑虹幇浜嗭紝涓轟粈涔坔ashset娣誨姞浜嗙浉絳夌殑鍏冪礌鍛紝榪欐槸涓嶆槸鍜宧ashset鐨勫師鍒欒繚鑳屼簡鍛紵鍥炵瓟鏄細娌℃湁
鍥犱負鍦ㄦ牴鎹甴ashcode()瀵逛袱嬈″緩绔嬬殑new Student(1,"zhangsan")瀵硅薄榪涜姣旇緝鏃訛紝鐢熸垚鐨勬槸涓嶅悓鐨勫搱甯岀爜鍊鹼紝鎵浠ashset鎶婁粬褰撲綔涓嶅悓鐨勫璞″寰呬簡錛屽綋鐒舵鏃剁殑 equals()鏂規(guī)硶榪斿洖鐨勫間篃涓嶇瓑錛堣繖涓笉鐢ㄨВ閲婁簡鍚э級銆傞偅涔堜負浠涔堜細鐢熸垚涓嶅悓鐨勫搱甯岀爜鍊煎憿錛熶笂闈㈡垜浠湪姣旇緝s1鍜宻2鐨勬椂鍊欎笉鏄敓鎴愪簡鍚屾牱鐨勫搱甯岀爜 鍚楋紵鍘熷洜灝卞湪浜庢垜浠嚜宸卞啓鐨凷tudent綾誨茍娌℃湁閲嶆柊鑷繁鐨刪ashcode()鍜宔quals()鏂規(guī)硶錛屾墍浠ュ湪姣旇緝鏃訛紝鏄戶鎵跨殑object綾諱腑鐨?hashcode()鏂規(guī)硶錛屽懙鍛碉紝鍚勪綅榪樿寰梠bject綾諱腑鐨刪ashcode()鏂規(guī)硶姣旇緝鐨勬槸浠涔堝惂錛侊紒
瀹冩槸涓涓湰鍦版柟娉曪紝姣旇緝鐨勬槸瀵硅薄鐨勫湴鍧錛堝紩鐢ㄥ湴鍧錛夛紝浣跨敤new鏂規(guī)硶鍒涘緩瀵硅薄錛屼袱嬈$敓鎴愮殑褰撶劧鏄笉鍚岀殑瀵硅薄浜嗭紙榪欎釜澶у閮借兘鐞嗚В鍚с傘傘傦級錛岄犳垚 鐨勭粨鏋滃氨鏄袱涓璞$殑hashcode()榪斿洖鐨勫間笉涓鏍楓傛墍浠ユ牴鎹涓涓噯鍒欙紝hashset浼氭妸瀹冧滑褰撲綔涓嶅悓鐨勫璞″寰咃紝鑷劧涔熺敤涓嶇潃絎簩涓噯鍒欒繘琛?鍒ゅ畾浜嗐傞偅涔堟庝箞瑙e喅榪欎釜闂鍛紵錛?
絳旀鏄細鍦⊿tudent綾諱腑閲嶆柊hashcode()鍜宔quals()鏂規(guī)硶銆?
渚嬪錛?
class Student
{
int num;
String name;
Student(int num,String name)
{
this.num=num;
this.name=name;
}
public int hashCode()
{
return num*name.hashCode();
}
public boolean equals(Object o)
{
Student s=(Student)o;
return num==s.num && name.equals(s.name);
}
public String toString()
{
return num+":"+name;
}
}
鏍規(guī)嵁閲嶅啓鐨勬柟娉曪紝鍗充究涓ゆ璋冪敤浜唍ew Student(1,"zhangsan")錛屾垜浠湪鑾峰緱瀵硅薄鐨勫搱甯岀爜鏃訛紝鏍規(guī)嵁閲嶅啓鐨勬柟娉昲ashcode()錛岃幏寰楃殑鍝堝笇鐮佽偗瀹氭槸涓鏍風殑錛堣繖涓鐐瑰簲璇ユ病鏈夌枒闂惂錛夈?
褰撶劧鏍規(guī)嵁equals()鏂規(guī)硶鎴戜滑涔熷彲鍒ゆ柇鏄浉鍚岀殑銆傛墍浠ュ湪鍚慼ashset闆嗗悎涓坊鍔犳椂鎶婂畠浠綋浣滈噸澶嶅厓绱犵湅寰呬簡銆傛墍浠ヨ繍琛屼慨鏀瑰悗鐨勭▼搴忔椂錛屾垜浠細鍙戠幇榪愯緇撴灉鏄細
1:zhangsan
3:wangwu
2:lisi
鍙互鐪嬪埌閲嶅鍏冪礌鐨勯棶棰樺凡緇忔秷闄ゃ?
鍏充簬鍦╤ibernate鐨刾ojo綾諱腑錛岄噸鏂癳quals()鍜宧ashcode()鐨勯棶棰橈細
1)錛岄噸鐐規(guī)槸equals錛岄噸鍐檋ashCode鍙槸鎶鏈姹傦紙涓轟簡鎻愰珮鏁堢巼錛?
2)錛屼負浠涔堣閲嶅啓equals鍛紝鍥犱負鍦╦ava鐨勯泦鍚堟鏋朵腑錛屾槸閫氳繃equals鏉ュ垽鏂袱涓璞℃槸鍚︾浉絳夌殑
3)錛屽湪hibernate涓紝緇忓父浣跨敤set闆嗗悎鏉ヤ繚瀛樼浉鍏沖璞★紝鑰宻et闆嗗悎鏄笉鍏佽閲嶅鐨勩傛垜浠啀鏉ヨ皥璋堝墠闈㈡彁鍒板湪鍚慼ashset闆嗗悎涓坊鍔犲厓绱犳椂,鎬庢牱鍒ゆ柇瀵硅薄鏄惁鐩稿悓鐨勫噯鍒欙紝鍓嶉潰璇翠簡涓ゆ潯錛屽叾瀹炲彧瑕侀噸鍐檈quals()榪欎竴鏉′篃鍙互銆?
浣嗗綋hashset涓厓绱犳瘮杈冨鏃訛紝鎴栬呮槸閲嶅啓鐨別quals()鏂規(guī)硶姣旇緝澶嶆潅鏃訛紝鎴戜滑鍙敤equals()鏂規(guī)硶榪涜姣旇緝鍒ゆ柇錛屾晥鐜囦篃浼氶潪甯鎬綆錛?鎵浠ュ紩鍏ヤ簡hashcode()榪欎釜鏂規(guī)硶錛屽彧鏄負浜嗘彁楂樻晥鐜囷紝浣嗘槸鎴戣寰楄繖鏄潪甯告湁蹇呰鐨勶紙鎵浠ユ垜浠湪鍓嶉潰浠ヤ袱鏉″噯鍒欐潵榪涜hashset鐨勫厓绱犳槸鍚﹂噸澶?鐨勫垽鏂級銆?
姣斿鍙互榪欐牱鍐欙細
public int hashCode(){
return 1;}//絳変環(huán)浜巋ashcode鏃犳晥
榪欐牱鍋氱殑鏁堟灉灝辨槸鍦ㄦ瘮杈冨搱甯岀爜鐨勬椂鍊欎笉鑳借繘琛屽垽鏂紝鍥犱負姣忎釜瀵硅薄榪斿洖鐨勫搱甯岀爜閮芥槸1錛屾瘡嬈¢兘蹇呴』瑕佺粡榪囨瘮杈僥quals()鏂規(guī)硶鍚庢墠鑳借繘琛屽垽鏂槸鍚﹂噸澶嶏紝榪欏綋鐒朵細寮曡搗鏁堢巼鐨勫ぇ澶ч檷浣庛?
鎴戞湁涓涓棶棰橈紝濡傛灉鍍忓墠闈㈡彁鍒扮殑鍦╤ashset涓垽鏂厓绱犳槸鍚﹂噸澶嶇殑蹇呰鏂規(guī)硶鏄痚quals()鏂規(guī)硶錛堟牴鎹綉涓婃壘鍒扮殑瑙傜偣錛夛紝浣嗘槸榪欓噷騫舵病鏈夋秹鍙婂埌鍏充簬鍝堝笇琛ㄧ殑闂錛屽彲鏄繖涓泦鍚堝嵈鍙玥ashset錛岃繖鏄負浠涔堬紵錛?
鎴戞兂錛屽湪hashmap,hashtable涓殑瀛樺偍鎿嶄綔錛屼緷鐒墮伒瀹堜笂闈㈢殑鍑嗗垯銆傛墍浠ヨ繖閲屼笉鍐嶅璇淬傝繖浜涙槸浠婂ぉ鐪嬩功錛岀綉涓婃煡璇㈣祫鏂欙紝鑷繁鎬葷粨鍑烘潵 鐨勶紝閮ㄥ垎浠g爜鍜岃璦鏄紩榪幫紝浣嗘槸鍗冪湡涓囩‘鏄嚜宸辨葷粨鍑烘潵鐨勩傛湁閿欒涔嬪鍜屼笉璇︾粏涓嶆竻妤氱殑鍦版柟榪樿澶у鎸囧嚭錛屾垜涔熸槸鍒濆鑰咃紝鎵浠ラ毦鍏嶄細鏈夐敊璇殑鍦版柟錛屽笇鏈涘ぇ 瀹跺叡鍚岃璁恒?

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