{"id":3004,"date":"2022-07-08T11:25:57","date_gmt":"2022-07-08T11:25:57","guid":{"rendered":"http:\/\/the-codest.localhost\/blog\/9-mistakes-to-avoid-while-programming-in-java\/"},"modified":"2026-03-09T13:13:14","modified_gmt":"2026-03-09T13:13:14","slug":"9-fejl-du-skal-undga-nar-du-programmerer-i-java","status":"publish","type":"post","link":"https:\/\/thecodest.co\/da\/blog\/9-mistakes-to-avoid-while-programming-in-java\/","title":{"rendered":"9 fejl, du skal undg\u00e5, n\u00e5r du programmerer i Java"},"content":{"rendered":"

Java<\/a><\/strong> er et popul\u00e6rt sprog med en etableret position i verden af softwareudvikling<\/a><\/strong>. Det er et st\u00e6rkt og alsidigt programmeringssprog. Omkring 3 milliarder enheder p\u00e5 verdensplan k\u00f8rer p\u00e5 Java<\/strong> og derfor blev der beg\u00e5et mindst 3 milliarder fejl, da den blev brugt. I denne artikel vil vi fokusere p\u00e5, hvordan man undg\u00e5r at lave flere.<\/p>\n\n\n\n

1. F\u00e5 undtagelse for samtidig \u00e6ndring<\/h2>\n\n\n\n

Det er langt den mest almindelige fejl, jeg er st\u00f8dt p\u00e5. I begyndelsen af min karriere begik jeg den ogs\u00e5 mange gange. Fejlen opst\u00e5r, n\u00e5r man fors\u00f8ger at \u00e6ndre samlingen, mens man itererer gennem den. Den ConcurrentModificationUdtagelse<\/code> kan ogs\u00e5 opst\u00e5, n\u00e5r du arbejder med flere tr\u00e5de, men lad os nu fokusere p\u00e5 et basisscenarie.<\/p>\n\n\n\n

Antag, at du har en Samling<\/code> af brugere, hvor nogle af dem er voksne, og andre ikke er. Din opgave er at filtrere b\u00f8rnene fra.<\/p>\n\n\n\n

for (Bruger : brugere) {\n\n   if (!user.isAdult()) {\n\n       users.remove(user);\n\n   }\n\n}\n<\/code><\/pre>\n\n\n\n
K\u00f8rer den f\u00f8rn\u00e6vnte Kode<\/a> ender med at f\u00e5 ConcurrentModificationUdtagelse<\/code>. Hvor gik vi galt i byen? F\u00f8r vi afsluttede vores iteration, fors\u00f8gte vi at fjerne nogle elementer. Det er det, der udl\u00f8ser undtagelsen.<\/p>\n\n\n\n
Hvordan kan jeg undg\u00e5 det?<\/h3>\n\n\n\n
Der er et par tilgange, der kan hj\u00e6lpe i det tilf\u00e6lde. F\u00f8rst og fremmest skal du drage fordel af Java<\/strong> 8's godhed - Str\u00f8m<\/code>.<\/p>\n\n\n\n
List adults = users.stream()\n\n       .filter(User::isAdult)\n\n       .toList();\n<\/code><\/pre>\n\n\n\n
Brug af en Pr\u00e6dikat<\/code> filter har vi gjort det omvendte af den tidligere betingelse - nu bestemmer vi, hvilke elementer der skal inkluderes. Fordelen ved en s\u00e5dan tilgang er, at det er nemt at k\u00e6de andre funktioner sammen efter fjernelsen, f.eks. kort<\/code>. Men pr\u00f8v for guds skyld ikke at g\u00f8re noget i stil med nedenst\u00e5ende:<\/p>\n\n\n\n
users.stream()\n\n       .filter(v -> !v.isAdult())\n\n       .forEach(users::remove);\n<\/code><\/pre>\n\n\n\n
Det kunne ogs\u00e5 ende i ConcurrentModificationUdtagelse<\/code> fordi du \u00e6ndrer str\u00f8mkilden. Det kan ogs\u00e5 give dig nogle flere undtagelser, som ikke er nemme at fejlfinde.<\/p>\n\n\n\n
At l\u00f8se ConcurrentModificationUdtagelse<\/code> i et single-thread-scenarie. Du kan ogs\u00e5 skifte til at bruge direkte Iterator<\/code> og dens fjern()<\/code> metoden, eller du kan simpelthen lade v\u00e6re med at fjerne elementer under iterationen. Min anbefaling er dog at bruge Vandl\u00f8b<\/code> - Det er 2022.<\/p>\n\n\n\n
2. Gemme adgangskoder som strenge<\/h2>\n\n\n\n
Da jeg bliver mere og mere involveret i cybersikkerhed, ville jeg ikke v\u00e6re tro mod mig selv, hvis jeg ikke n\u00e6vnte mindst \u00e9n Java-fejl<\/strong> der kan f\u00f8re til et sikkerhedsproblem. Lagring af adgangskoder modtaget fra brugere i en Streng<\/code> objekt er netop noget, du skal v\u00e6re bange for.<\/p>\n\n\n\n
Problemet (eller m\u00e5ske fordelen) ved Streng<\/code> er, at den er uforanderlig. I cyberverdenen skaber det en potentiel trussel, da du ikke kan slette v\u00e6rdien af en engang oprettet Streng<\/code> objekt. Den angriber, der f\u00e5r adgang til din computers hukommelse, kan finde adgangskoder i klartekst der.<\/p>\n\n\n\n
For det andet er strenge i Java<\/strong> internaliseres af JVM'en og gemmes i PermGen-rummet eller i heap-rummet. N\u00e5r du opretter en Streng<\/code> objektet, bliver det cached, og det bliver f\u00f8rst fjernet, n\u00e5r Garbage Collector begynder at g\u00f8re sit arbejde. Du kan ikke v\u00e6re sikker p\u00e5, hvorn\u00e5r din adgangskode bliver slettet fra String-poolen, da Garbage Collector arbejder p\u00e5 en ikke-deterministisk m\u00e5de.<\/p>\n\n\n\n
Hvordan undg\u00e5r man det?<\/h3>\n\n\n\n
Den anbefalede tilgang er at bruge char[]<\/code> eller, endnu bedre, et bibliotek, der underst\u00f8tter lagring af adgangskoder som char[]<\/code>f.eks.Password4j<\/a>. Den char[]<\/code> er foranderlig og kan \u00e6ndres, efter at den er blevet initialiseret. N\u00e5r du har behandlet en adgangskode, kan du bare slette char[]<\/code> password-array ved at skrive tilf\u00e6ldige tegn i det. Hvis angriberne f\u00e5r adgang til din computers hukommelse, vil de kun se nogle tilf\u00e6ldige v\u00e6rdier, som ikke har noget at g\u00f8re med brugernes adgangskoder.<\/p>\n\n\n\n
3. (U)h\u00e5ndtering af undtagelser<\/h2>\n\n\n\n
Nybegyndere og ogs\u00e5 mere avancerede programm\u00f8rer ved ikke, hvordan de skal h\u00e5ndtere undtagelser korrekt. Deres st\u00f8rste synd i den forbindelse er bare at ignorere dem. DET ER ALDRIG EN GOD TILGANG.<\/p>\n\n\n\n
Desv\u00e6rre kan vi ikke give dig en universall\u00f8sning, der passer til alle. Undtagelse<\/code>s' scenarie, du st\u00f8der p\u00e5. Du skal t\u00e6nke p\u00e5 hvert enkelt tilf\u00e6lde. Men vi kan give dig nogle r\u00e5d om, hvordan du kommer i gang med det emne.<\/p>\n\n\n\n
Hvordan kan jeg undg\u00e5 det?<\/h3>\n\n\n\n
    \n
  1. \n
    Ignorerer Undtagelse<\/code>er aldrig en god praksis. Undtagelse<\/code>s er smidt ind af en eller anden grund, s\u00e5 du b\u00f8r ikke ignorere dem.<\/p>\n<\/li>\n\n\n\n
  2. \n
    try {...} catch(Exception e) { log(e); }<\/code> er sj\u00e6ldent den rigtige tilgang til Undtagelse<\/code> h\u00e5ndtering.<\/p>\n<\/li>\n\n\n\n
  3. \n
    Kast Undtagelse<\/code>vise en fejldialog til brugeren eller i det mindste tilf\u00f8je en omfattende besked til loggen.<\/p>\n<\/li>\n\n\n\n
  4. \n
    Hvis du ikke har h\u00e5ndteret dine undtagelser (hvilket du ikke b\u00f8r), s\u00e5 forklar dig i det mindste i kommentaren.<\/p>\n<\/li>\n<\/ol>\n\n\n\n
    4. Brug af nul<\/h2>\n\n\n\n
    Desv\u00e6rre er det ret almindeligt at finde en Java-funktion, der i nogle tilf\u00e6lde returnerer en nul<\/code>. Problemet er, at en s\u00e5dan funktion tvinger sin klient til at udf\u00f8re et null-tjek p\u00e5 resultatet. Uden det vil NullPointerUdtagelse<\/code> bliver kastet.<\/p>\n\n\n\n
    Den anden ting er at sende en nul<\/code> v\u00e6rdi. Hvorfor t\u00e6nkte du overhovedet p\u00e5 det? I et s\u00e5dant tilf\u00e6lde skal funktionen udf\u00f8re et null-check. N\u00e5r man bruger tredjepartsbiblioteker, kan man ikke \u00e6ndre funktionernes inderside. Hvad g\u00f8r man s\u00e5?<\/p>\n\n\n\n
    Endnu vigtigere er det, at andre udviklere, der l\u00e6ser din kode og ser, at du passerer nul<\/code> vil nok v\u00e6re forvirret over, hvorfor du v\u00e6lger en s\u00e5 bizar m\u00e5de at implementere din funktion p\u00e5.<\/p>\n\n\n\n
    Hvordan kan jeg undg\u00e5 det?<\/h3>\n\n\n\n
    Returner ikke en nul<\/code> v\u00e6rdi! Nogensinde! Hvis din funktion returnerer en eller anden form for Samling<\/code>kan du bare returnere en tom Samling<\/code>. Hvis du arbejder med enkeltobjekter, kan du bruge designm\u00f8nsteret for null-objekter. Siden Java<\/strong> 8, er det implementeret som Valgfrit<\/code>. Bortset fra det er den mindst anbefalede fremgangsm\u00e5de at rejse en Undtagelse<\/code>.<\/p>\n\n\n\n
    5. Tung sammenk\u00e6dning af strenge<\/h2>\n\n\n\n
    Forh\u00e5bentlig er det ikke en fejl, du beg\u00e5r, da det er det mest popul\u00e6re (eller m\u00e5ske n\u00e6stmest popul\u00e6re efter FizzBuzz) interviewsp\u00f8rgsm\u00e5l. Som du burde vide nu, er en Streng<\/code> objektet er uforanderligt i Java<\/strong> - N\u00e5r den f\u00f8rst er oprettet, kan den ikke \u00e6ndres. S\u00e5 sammenk\u00e6dning af Streng<\/code> bogstaver betyder en masse un\u00f8dvendig hukommelsesallokering. Sammenk\u00e6dning af Streng<\/code> objekter hver gang kr\u00e6ver oprettelse af en midlertidig StringBuilder<\/code> objekt og \u00e6ndre det tilbage til en streng. Derfor er denne l\u00f8sning absolut ikke egnet, hvis vi \u00f8nsker at kombinere et stort antal tegn.<\/p>\n\n\n\n
    Hvordan kan jeg undg\u00e5 det?<\/h3>\n\n\n\n
    For at l\u00f8se det problem skal du bruge StringBuilder<\/code>. Det skaber et foranderligt objekt, som let kan manipuleres. Du kan selvf\u00f8lgelig altid bruge StringBuffer<\/code> hvis din projekt<\/a> bruges i en samtidig kontekst.<\/p>\n\n\n\n
    6. Ikke at bruge eksisterende l\u00f8sninger<\/h2>\n\n\n\n
    N\u00e5r man udvikler software, er det et must at kende det grundl\u00e6ggende i det sprog, man skriver i, men det er ikke nok. Mange algoritmiske problemer, du st\u00f8der p\u00e5, n\u00e5r du implementerer en ny funktion, er allerede blevet l\u00f8st af en anden. Alt for mange gange har jeg set nogen implementere en sikkerhedsalgoritme fra bunden. En s\u00e5dan tilgang er fejlbeh\u00e6ftet. En person kan ikke teste en s\u00e5 kompleks l\u00f8sning grundigt. Den kollektive viden hos hold<\/a> der best\u00e5r af middelgode programm\u00f8rer, er n\u00e6sten altid bedre end et enkelt vidunderbarns storhed. Java-udvikler<\/a><\/strong>. Du beh\u00f8ver ikke at opfinde den dybe tallerken igen - du skal bare tilpasse den eksisterende l\u00f8sning, s\u00e5 den passer til dine behov.<\/p>\n\n\n\n
    Hvordan kan jeg undg\u00e5 det?<\/h3>\n\n\n\n
    Pr\u00f8v at s\u00f8ge efter biblioteker, der behandler det problem, du arbejder med. Pr\u00f8v at finde lignende l\u00f8sninger. Mange af de biblioteker, der er tilg\u00e6ngelige p\u00e5 web<\/a> er gratis og er blevet finpudset og testet af erfarne udviklere og hele Java-samfundet. V\u00e6r ikke bange for at bruge dem.<\/p>\n\n\n\n
    7. Ikke tid nok til at skrive test<\/h2>\n\n\n\n
    Det er fristende at tro, at vores kode altid vil k\u00f8re perfekt. Ikke at skrive test til kode er den v\u00e6rste synd i Java softwareudviklere<\/a><\/strong>. Mange af os<\/a> foretr\u00e6kker manuelle og udforskende tests i stedet for enhedstests, hvilket er sk\u00f8rt.  Hvorfor spilde tid p\u00e5 at skrive tests, n\u00e5r du kan fokusere p\u00e5 at levere verdens bedste kode til dit projekt, som SLET ikke har nogen fejl? Det viser sig, at virkeligheden er brutal, og vi kan ikke levere kode af h\u00f8j kvalitet uden at skrive tests.<\/p>\n\n\n\n
    Hvordan kan jeg undg\u00e5 det?<\/h3>\n\n\n\n
    Du b\u00f8r altid forberede tests til din kode. Jeg ved godt, at TDD-tilgangen ikke er s\u00e5 nem at vedligeholde, men du b\u00f8r i det mindste lave tests, der d\u00e6kker alle de situationer, hvor din kode kan k\u00f8re. Det inkluderer test af ekstraordin\u00e6re situationer. Unit-tests er n\u00f8dvendige. Du er n\u00f8dt til at lave dem for hver funktion i dit projekt, hvis du vil sikre dig, at din kode er nem at refaktorere og udvide i den videre udvikling. <\/p>\n\n\n\n
    En ting mere. Oprethold en h\u00f8j standard for din testkode - det er det hele v\u00e6rd. Det er onkel Bobs r\u00e5d, og jeg er helt enig i det.<\/p>\n\n\n\n
    Glem heller ikke andre typer af tests. Integrationstest er en ting, du b\u00f8r overveje i alle dine projekter.<\/p>\n\n\n\n
    8. Glem alt om adgangsmodifikatorer<\/h2>\n\n\n\n
    Privat og offentligt, ikke sandt? Hvordan kan vi glemme dem? Det viser sig, at der er flere. Da du f\u00f8rst begyndte at l\u00e6re Java<\/strong>har du helt sikkert l\u00e6rt om beskyttede adgangsmodifikatorer. De kan v\u00e6re nyttige i nogle tilf\u00e6lde, s\u00e5 det er v\u00e6rd at kende til deres eksistens.<\/p>\n\n\n\n
    Java-udviklere<\/a><\/strong> synes ofte at glemme pakkeomfanget. Det er let ikke at huske at bruge det, da det er implicit og ikke kr\u00e6ver nogen Java<\/strong> n\u00f8gleord. Pakkeomfanget er vigtigt. Det giver dig mulighed for at teste en beskyttet metode. Beskyttede elementer er tilg\u00e6ngelige fra testklassens sti, s\u00e5 l\u00e6nge pakken er den samme.<\/p>\n\n\n\n
    Hvordan kan jeg undg\u00e5 det?<\/h3>\n\n\n\n
    Husk den beskyttede modifikator, og at pakkens omfang giver dig mulighed for at teste den.<\/p>\n\n\n\n
    9. Brug af ren JavaEE i stedet for Spring<\/h2>\n\n\n\n
    Det n\u00e6ste skridt efter l\u00e6ring Java<\/strong> SE er at l\u00e6re at k\u00f8re Java<\/strong> p\u00e5 servere, hvordan man laver en applikation p\u00e5 virksomhedsniveau.<\/p>\n\n\n\n
    Nybegyndere falder ofte i en f\u00e6lde, n\u00e5r de skal l\u00e6re JavaEE, da der findes et stort antal tutorials om det. Selv 'Thinking in Java', den Java-programm\u00f8rer<\/strong>' n\u00e6vner JavaEE og siger ikke noget om de andre muligheder.<\/p>\n\n\n\n
    Hvordan kan jeg undg\u00e5 det?<\/h3>\n\n\n\n
    JavaEE er en sang fra fortiden. I dag er Spring en go-to-ting, og Java EE er bare rart at have. Alle moderne applikationer p\u00e5 virksomhedsniveau bruger Spring, s\u00e5 du b\u00f8r kraftigt overveje at l\u00e6re det her<\/a>.<\/p>\n\n\n\n
    \"M\u00f8d<\/a><\/figure>\n\n\n\n
    L\u00e6s mere om det:<\/strong><\/p>\n\n\n\n
    Den rigtige m\u00e5de at finde de bedste Java-udviklere p\u00e5<\/a><\/p>\n\n\n\n
    Den bedste type projekter til Java<\/a><\/p>\n\n\n\n
    De bedste programmeringssprog til fintech-virksomheder<\/a><\/p>","protected":false},"excerpt":{"rendered":"
    Hvilke fejl b\u00f8r man undg\u00e5, n\u00e5r man programmerer i Java? I det f\u00f8lgende afsnit besvarer vi dette sp\u00f8rgsm\u00e5l.<\/p>","protected":false},"author":2,"featured_media":3005,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[15,8],"tags":[],"class_list":["post-3004","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-fintech","category-software-development"],"acf":[],"yoast_head":"\n9 Mistakes to Avoid While Programming in Java - The Codest<\/title>\n<meta name=\"description\" content=\"Explore 9 Java coding mistakes developers should avoid to improve code quality, security, and performance in modern Java applications.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/thecodest.co\/da\/blog\/9-fejl-du-skal-undga-nar-du-programmerer-i-java\/\" \/>\n<meta property=\"og:locale\" content=\"da_DK\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"9 Mistakes to Avoid While Programming in Java\" \/>\n<meta property=\"og:description\" content=\"Explore 9 Java coding mistakes developers should avoid to improve code quality, security, and performance in modern Java applications.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/thecodest.co\/da\/blog\/9-fejl-du-skal-undga-nar-du-programmerer-i-java\/\" \/>\n<meta property=\"og:site_name\" content=\"The Codest\" \/>\n<meta property=\"article:published_time\" content=\"2022-07-08T11:25:57+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-03-09T13:13:14+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/thecodest.co\/app\/uploads\/2024\/05\/9_mistakes_to_avoid_while_programming_in_java.png\" \/>\n\t<meta property=\"og:image:width\" content=\"960\" \/>\n\t<meta property=\"og:image:height\" content=\"540\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"thecodest\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"thecodest\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"8 minutter\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/thecodest.co\\\/blog\\\/9-mistakes-to-avoid-while-programming-in-java\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/thecodest.co\\\/blog\\\/9-mistakes-to-avoid-while-programming-in-java\\\/\"},\"author\":{\"name\":\"thecodest\",\"@id\":\"https:\\\/\\\/thecodest.co\\\/#\\\/schema\\\/person\\\/7e3fe41dfa4f4e41a7baad4c6e0d4f76\"},\"headline\":\"9 Mistakes to Avoid While Programming in Java\",\"datePublished\":\"2022-07-08T11:25:57+00:00\",\"dateModified\":\"2026-03-09T13:13:14+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/thecodest.co\\\/blog\\\/9-mistakes-to-avoid-while-programming-in-java\\\/\"},\"wordCount\":1643,\"commentCount\":0,\"publisher\":{\"@id\":\"https:\\\/\\\/thecodest.co\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/thecodest.co\\\/blog\\\/9-mistakes-to-avoid-while-programming-in-java\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/thecodest.co\\\/app\\\/uploads\\\/2024\\\/05\\\/9_mistakes_to_avoid_while_programming_in_java.png\",\"articleSection\":[\"Fintech\",\"Software Development\"],\"inLanguage\":\"da-DK\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\\\/\\\/thecodest.co\\\/blog\\\/9-mistakes-to-avoid-while-programming-in-java\\\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/thecodest.co\\\/blog\\\/9-mistakes-to-avoid-while-programming-in-java\\\/\",\"url\":\"https:\\\/\\\/thecodest.co\\\/blog\\\/9-mistakes-to-avoid-while-programming-in-java\\\/\",\"name\":\"9 Mistakes to Avoid While Programming in Java - 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