"if(map.get(key)-map1.getOrDefault(key, 0)!=0)" 和 "if(map.get(key)!=map1.getOrDefault(key, 0))" 有什么区别

Question

我有以下代码-

package DP.permutation_in_string;

import java.util.HashMap;
import java.util.Map;

public class LeetCode {
    public static boolean checkInclusion(String s1, String s2) {
        Map<Character, Integer> map = new HashMap<>();
        
        for(int i=0; i<s1.length(); i++){
            map.put(s1.charAt(i), map.getOrDefault(s1.charAt(i), 0)+1);
        }

        for(int i=0; i<=s2.length()-s1.length(); i++){
                Map<Character, Integer> map1 = new HashMap<>();
         
                for(int j=i; j<i+s1.length();j++){
                    map1.put(s2.charAt(j), map1.getOrDefault(s2.charAt(j),0)+1);
                }
                
                if(mapCompare(map, map1))
                    return true;
        }
        
        return false;
    }
    
    static boolean mapCompare(Map<Character, Integer> map, Map<Character, Integer> map1){
        for(char key:map.keySet())
            //if(map.get(key)!=map1.getOrDefault(key, 0))
            if(map.get(key)-map1.getOrDefault(key, 0)!=0)
                return false;
        
        return true;
    }
    public static void main(String[] args) {
        String s1="ckzviabspcfbabslodcxtzanlsnwbqrozvnfadhtskosxhxaxzwcthvirwivsfuyxgkdvvdmmaoohvnfegkzdajhzibfiuxvsihpseyyiapmgldyojfselzzudzrxcksvfoqoeimyfhnvidryqhhpvjawwpzspcfnvmewnhcbbbwfjifmcuspbrrjyhcusyiuydscwenyicdlfzaoaiudsdyjmhmzwmeaozheiaddevjrrgsfgqnyeoyxfvktctazsfizkynlookeorzmdvtloyfpbqjgzhjvykdthwkuubnbalrddjxpizysaptrinlytecouekkpsfzbjaitckodcdinydtaaakbntwbvrcabylllxtgtkdqfkjggvbrnxnvcsfpcutabvazyeqzitpwhhdpcxaklhbjrcsqzveytzbgoeqnyrbkvkfnlqhrnedjomfmkuadwabnzomgvtdypocbvipryedcxnrcrqwpefqducxxilhpoewlliilidxucjydpahcumngpekrlroftwpbaejfjmohnkulxdglcpcszpyqestonhxskshzmdkikjkeymddyiysmigvqjveocbabhcofwyseytwfgiqmufcqrugwofytxzwwwiwlxdshtamwneosotqbfjjdxmhjkmzcvpmkuumycqzvlmwvjdwkcikyewupwaotrseyomhuykdkohveftgqfoqjcnstlxdasnvimslmuqsqrhvbukyfvpswmlavtxegbcesxgzswwnslxymmrdwmpalcazukvyyotlvwvlishtgbmlznrmcjysjemwqfjgbehnowgjlvtgemlkkdqpxiuqwhqkqdkexoflxfescoblknurkntbpfqfiervqgeiasguycmjoyzyujgzdfjobrswjpxixmadnnkdtazbasmnnlbubokkvomtupdpqwnoddummmqbwbthfhqdgdawdwxlmgvelhefvqcrpxbkgvhyrpxmfivrvkkqfpxjhzqesiqoeanqzpvbgonwptzqgtajoiiphivxtefarwjyoklkxumrndswebdsgiipzrcunpnibmxwlkihnzlswaujflztxxnuhojrpkzldwhnuiizxalawskkvaplopthvzjrbqfwpwjfkzrhyciajdsaeusctnvajuubjiqdqsaqjxtxgxabpdwxzgiedyyeosfdbkairekywkilyksjratftctphompqoomxucysbzrpywjzumoiizklkooilgeapimiixawfgiszfqucihxfrtrwijyeiebudncwnxbnafohhhqaltksafjfegxlbbewetsyrtuxxlngffpcnyfdarqwznsuiuhvqshjpvbiqkxgfwyrkdlorlwgexfinunbfzifxlfufalbkyfdekhupuuflsetpbppaahwbtjpjguygpnavimbbaeikwjxurdxyfgmldgdbkyxzhvwlxzlpnpmzlyosvhngmuqkrvcsabhiahhguxuakphuaptbjfpxybqnlfazkagwlbvzcnzorpymafiwvtkjtilwihwoyelogtpdyipzkurqcghpdqgrfpnmrmahbkbyupxwooblaydongjrlnuhoikoyiexgzlzgonceyhfwypsgypilxcnkdhxvbfddnhvdicolrjyzttrymmcvoyswaszbbugsuuewhewtoxgnrbfqsysjqqcutoikssesxaohxxfxofiguvpgzfkimmqdjuyljlpndapzygidopwxnaetmmpyaqozybbpfqlonebiilvckmtyaommksfcrmdeyjjbjncmpruofaaccnvndkovjugcrzcwkbdhqdiwnvnavnngloshyataygyukrecamzftmeephucmofjgrzsexsprpdkazhmtaepqppgzjmxxzlpbkouqlhqcxdpaslrjrsnfbjvbekpyqsldzhxarpzbbjteudfwfjdipgcdwylorxivwbjkegazpcngzkokygjfnmfeumbetznsxsmyhccurqdzznvhrtawpklrrrbedqzkiczignlaoaiydezgktdecaxwxxecymbuisvhlcjlhmnpjuegnaawfxopvvkxihehquxzlveabigomeptsqbfurytjikpbtsotgfghadilylnimxcsvgtmzjgxjyhabtfawzmomctquctwnolglflghdugeutgdmkitunbkhgoceqyrzvwprotiysaiqcnwxflcjgjqobeskizjqqwihnmxyvbeeufyvouupnyuuyauxtmhtqlbgoacjdkvmuqohbkpctfwxvwlghevsuozrgxkrrrllnvjloeligxvnvzluxlajszgeilxdjaviawhlthtxuclqypgdiwgwrhynmzqghyzeednlmyepgxxvtmjsuprisbgyvcojhculwdkjmpmvueaftiujrmdqptrmlrwdyjtjlznuhftzmffbcqsjemrpjrqxtuxhlnqvckgcuvhswgtxonfljjwnexdafpjzwjdypdfwhwogikkpsvuckmgehcqmdecriamdqsdsxuhsdqenrpifzjnpvrbpvetatbmvsncltabzspzedumeclbxiqnsmdkbqfedikoalfsnxkhewwzyeqxlecfimvdpxdnvrtlxlxzakupknvchursvilyjyfxmvdeojclhjjwxtpqiogsfdnzchrlztvxmibbociiberaevpjmyqxvcicxuwkmyjlgxhvrjdqbjzdctzwidoplkvazhgsdbkavmrpfjgebydmloykqtxocdhcpwrtvawhofvwnohtwodppmcrbhvrvexzijiwgkptntyljvikjlzpjvpxaejfwzyldxrckbzylvhpqmjjeyatmrbcgozvcalcctngwuysjqmkmhjwmyyfxhdjswimahqzptrphtjekkabpgopfdnhwaclxzavftmswadgztxceonrkczurtdvxhabiafyzdbdbyorerekjzgpueihiamlscdndjjgqwdjsmeweqrfpypfrfsciclvrrqchnmtxscbvbbipzingkeopuvlnpqaeqidlpvusbkjhntvxbookqctymjmhqjvsnaiblmnofxphanpxspmkmxmyejooqpytdixgguonbpaipurpwwfqxrrtekvvtpgndabbvjcoxonxciuypxqcfolxirvafnmgsrcrenwyuxfekuqyfdtvhvmonvkstbmvygsbguiknltpixsebxktczniurulxpyxckrtmhpvgqpbvlqwvcqwaocalqtdwomgrjyvryodeikbeeebcrrkugliqgktoohsneynmfafykpmndfgwtpdwfrmicenyntbfyyntlqqrujfioycrhopgiadmsjcycucyuqvzufbvachmlwyfxspzrvkkvkhuykoqrwshzmyypmvosuezpsgtqtecayj";
        String s2="livsugnixbcmmajhinduvzfjzxtzneixibupxfezifaovcbowfayjtlcdsjogjytuczxbwluiktkdyecquebuvkgfobhpiqfbyckfbchvfkdowckrvuiblhbmubugrrovdhbyvevwetlusthiyxgtaqcdfytgbkrnnjifdslzntgnryqcmwkumdvqctymyffanmawobfihsfqmtqvivvouunsexpzcfmiituppwxgjyspyoeuspyystyneoonatbojiufzhhfeakqzeypaopkyscadbkzsnnjewgflysazhwaigicrzeccanemfmrvrdzxtcbuqvjblrynlhbmtkzhtiqnhrfclxovtijwucgvsreirqmhweoazxdyydksrchvizmljhdkekaxbqkleaolqnepijxpwbcxfadfsxswhzmmffsmoiyfosbwjjcgqpexddwizaiqpsaagwxkajdhqeyouihwlfrmnelakembxwcrvwqyaguvqewjczfmfqiqmjbqxcmfrpqoewszkomwckfgrlkannjefxsulbpkpxlvbrgwruvhdonuezoomvnyridrosfzhfvhmqbzdsfvjgfdqvafheuhveaqwrofhgkfobkkevdsqyumzrvapfjypvjsdzaxxwcnsbxasqewmkmucxbgjqntdsvrbndebttkoiznatcjgtgklljurkkdvpbrtbolvgrqwsnuoubhgvtmbakwgvxypndpqtireuvbdxfjcioqqsbfrqahqsfbwfnlkwobnqdbptxrizourrxyjejflgkbcwmrtttqeeqkyzrzdcfakwcfajhjfmcpnsbekwtzgpbwrotgsxopaemsnywoxsqxoyricgosfurfggulchgyoocivnkqytgbroijmaduoywbudtgwugekikebdadoygtmikcficifdcsvritesbvznlbrgbveudwzatarhbehowrrakimocgqyxzedhlqxzxtqloupbwbdvewcbehkmoahoykouhilivtxukqhwmyjjqmfxqybahsubfvnhctudtpxwsnwfmsamavjkqiabzzcqgqssygswavqpdtxfyognqybsogsbkzkktfjqebhitvqnawokacbkfkthqoammdscyvxgaaqyaplexhlwweambfwtylvihpdedshaeluxgthrejkgkvwrtyzpuygqghtlkmpnzkyjiwyuaqijkxttvdsxddfkmgnnlmamjumsbjmjxqkrgncrwyoyetdsmtanoasirkfklcsxukfdebnlbgobwgyqrthzwjbwpxuxmheplqyjaucgrptfewjahejsfypktnpafmlrzekbjqsgthrwbdxttitsqyglsjgnzmscncgvkooxdlxsmmugeeayicndgoagpfckerzuwdphqksijniyckzviabspcfbabslodcxtzanlsnwbqrozvnfadhtskosxhxaxzwcthvirwivsfuyxgkdvvdmmaoohvnfegkzdajhzibfiuxvsihpseyyiapmgldyojfselzzudzrxcksvfoqoeimyfhnvidryqhhpvjawwpzspcfnvmewnhcbbbwfjifmcuspbrrjyhcusyiuydscwenyicdlfznoaiudsdyjmcmzwmeaozheiaddevjrrgsfgqnyeoyxfvktctazsfizkynlookeorzmdvtloyfpbqjgzhjvykdthwkuubnbalrddjxpihysaptrinlytecouekkpsfzbjaitckodcdinydtaaakbntwbvrcasylllxtgtkdqfkjggvbanxnvcsfphutabvazyeqzitpwhhdpcxaklhbjrcsqzveytzbgoeqnyrbkvkfnlqhrnedjomfmkuadwabnzomgvtdypocbvipryedcxnrcrqwpefqducxxilhpoewlliilidxucjydpahcumagpekrlroftwpbaejfjmohnkulxdglcpcszpyqestonhxskshzmdkikjkeymdfyiysmigvqjveocbabhcofwyseytwfgiqmufcqrugwofytxzwwwiwlxdshtamwneosotqbfjjdxmhjkmzcvpmkuumycqzvlmwvjdwkcityewupwaotrseyomhuykdkohveftgqfoqjcnstlxdasnvimslmuqsqrhvbukyfvpswmlavtxegbcesxgzswwnslxymmrdwmpalcazukvyyotlvwvlishtgbmlznrmcjysjemwqfjgbehnowgjlvtgemlkkdqpxiuqwhqkqdkexoflxfescoblknurkntbpfqfiervqgeiesguycmjoyzyujgzdfjobrswjpxixmadnnkdtazbasmnnlbubokkvomtupdpqwnoddummmqbwbthfhqdgdawdwxlmgvelhefvqcrpxbkgvhyrpxmfivrvkkqfpxjhzqesiqoeanqzpvbgonwptzqgtajoiiphivxtefarwjyoklkxumrndswebdsghipzrcunpnibmxwlkihnzlswaujflztxxnuhojrpkzldwhnuiizxalawskkvaplopthvzjrbqfwpwjfkzrhyciajdsaeusctnvajuubjiqdqsaqjxtxgxabpdwxzgiedyyeosfdbkrirekywkilyksjratftctphompqoomxucysbzrpywjzumoiizklkooilgeapimiixawfgiszfqucihxfrtrwijyeiebudncwnxbnafohhhqaltksafjfegxlbbewetsyrtuxxlngffpcnyfdarqwznsuiuhvqshjpvbiqkxgfwyrkdlorlwgexfinunbfzifxlfufalbkyddekhupuuflsetpbppaahwbkjpjguygpnavimbbaeikwjxurdxyfgmldgdbkyxzhvwlxzlpnpmzlyosvhngmuqkrvcsabhiahhguxuakphuaptbjfpxybqnlfazkagwlbvzcnzorpymafiwvtkjtilwihwoyelogtpdyipzkurqcghpdqgrfpnmrmahbkbyupxwooblaydongjrlnuhoikoyiexgzlzgonceyhfwypsgypilxcnkdhxvbfddnhvdicolrjyzttrymmcvoyswaszbbugsuuewhawtoxgnrbfqsysjqqcutoikssesxaohxxfxofiguvpgzfkimmqdjuyljlpndapzygidopwxnaetmmpyaqozybbpfqlonebiilvckmtyaommksfcrmdeyjjbjncmpruofaaccnvndkovjugcrzcwkbdhqdiwnvnavnngloshyataygyukrecamzftmeephucmofjgrzsepsprpdkazhmtaepqppgzjmxxzlpbkouqlhqcxdpaslrjrsnfbjvbekpyqsldzhxarpzbbjteudfwfjdipgcdwylorxivwbjkegazpcngzkokygjfnmfeumbetznsxsmyhccurqdzznvhrtawpklrrrbedqzkiczignlaoaiydezgktdecaxwxxecymbuisvhlcjlhmnpjuegnaawfxopvvkxihehquxzlveabigomeptsqbfurytjikpbtsotgfghadilylnimxcsvgtmzjgxjyhabtfawzmomctquctwnolglflghdugeutgdmkitunbkhgoceqyrzvwprotiysaiqcnwnflcjgjqobeskizjqqwihnmxyvbeeufyvouupnyuuyauxtmhtqlbgoacjdkvmuqohbkpctfwxvwlgievsuozrgxkrrrllnvjloeligxvnvzluxlajszgeilxdjaviawhlthtxuclqypgdiwgwrhynmzqghyzeednlmyepgxxvtmjsuprisbgyvcojhculwdkjmpmvueaftiujrmdqptrmlrwdyjtjlznuhftzmffbcqsjemrpjrqxtuxhlnqvckgcuvhswgtxonfljjwnexdafpjzwjdypdfwhwogikkpsvuckmgehcqmdecriamdqsdsxuhsdqenrpifzjnpvrbpvetatbmvsncltabzspzedumeclbxiqnsmdkbqfedikoalfsnxkhewwzyeqxlecfimvdpxdnvrtlxlxzakupknvchursvilyjyfxmvdfojclhjjwxtpqiogsfdxzczrlztvxmibbociiberaevpjmyqxvcicxuwkmyjlgxhvrjdqbjzdctzwidoplkvazhgsdbkavmrpfjgebydmloykqtxocdhcpwrtvawhofvwnohtwodxpmcrbhvrvexzijiwgkptntyljvikjlzpjvpxaejfwzyldxrckbzylvhpqmjjeyatmrbcgozvcalcctngwuysjqmkmhjwmyyfxhdjswimahqzptrphtjekkabpgopfdnhwaclxzavftmswadgztxceonrkczurtdvxhabiafyzdbdbyorerekjzgpueihiamlscdndjjgqwdjsmeweqrfpypfrfsciclvrrqchnmtxscbvbbipzingkeopuvlnpqaeqidlpvusbkjhntvxbookqctymjmhqjvsnaiblmnofxphanpxspmkmxmyejooqpytdixgguonbpaipurpwwfqxrrtekvvtpgndabbvjcoxonxciuypxqcfolxirvafnmgsrcrenwyuxeekuqyfdtvhvmonvkbtbmvygsbguiknltpixsebxktczniurulxpyxckrtmhpvgqpbvlqwvcqwaocalqtdwomgrjyvryodeikbeeebcrrkugliqgktoohsneynmfafykpmndfgwtpdwfrmicenyntbfyyntlqqrujfioycrhopgiadmsjcycucyuqvzufbvachmlwyfxspzrvkkvkhuykoqrwshzmyypmvosuezpsgtqtecayjdasrysrmdewxmqntqmuavczczrcrzokjzqtiucdfmijfqkizfftxsddkdwlofkjbuhzodgzeslpezdifpdfktufgekrrbsxfeqduphoemwhncbblqkoyychuwlkjfxjmvdasfhwxnxjmstabgiujditpmpnojsfzpgqvupkdipphutiewfynvoxmdaloyxsksaxnyyizreshgejskhokarxddrrkoeglwledovrbarhkfcetrshiuucmbrtqjawsavbhuoijshkzcmogbjurybhwduushlmhjzgthhlvftpytayjzzbcxbtvozwhsmtkltgrugyfaoldnnswbohpsqvwbwtjcxeewsvfwpkwltxmomlwsylwvcmmrwjvvbbktqxnypfmhjigzaqacmprjfnooinkgbjzzwyuafxsmqdcmsxhbfoejjzxizufvfejrrcfaijqovlxdngkgwisvryevivawbcttftuxympktxbxotvdycxhfokmtdeqacdceffvhvjpnzfuhqslixvlcxehvbkritokoqqlbmkdkgflthhhdgiaidjjpvcatctiosolfqzcjmdppttztpklgosnshspna";
        System.out.println(checkInclusion(s1, s2));
    }

}

使用 if(map.get(key)-map1.getOrDefault(key, 0)!=0) 可以正常工作，但不能 if(map.get(key)!=map1.getOrDefault(key, 0))。这背后的原因是什么？

Answer 1

地图存储引用类型的键和值。您的地图存储 Integers.

map.get(key) 是一个 Integer，map1.getOrDefault(key, 0) 也是。如果您使用 != 比较它们，您正在比较 identity 的引用；也就是说，它们是同一个实例吗？例如，new Integer(0) == new Integer(0) 是假的，即使它们都是 Integer 的实例，包裹了 int 0.

但是，如果减去两个 Integer，它们将被取消装箱，因为二进制数字提升。 new Integer(0) - new Integer(0) == 0，因为每个 new Integer(0) 都拆箱到 0，而 0 - 0 == 0.

如果您使用 !A.equals(B) 而不是 A != B，您会得到相同的答案，因为这是比较（不）相等，而不是同一性。例如：

if(!map.get(key).equals(map1.getOrDefault(key, 0)))

或者，您可以使用 Integer.compare:

if(Integer.compare(map.get(key), map1.getOrDefault(key, 0)) != 0)

或显式拆箱：

if(map.get(key).intValue() != map1.getOrDefault(key, 0).intValue())