202004 GDG Incheon 나쁜 프로그래밍 습관

나쁜 프로그래밍 습관 (영진출판) - 202004 GDG Incheon 북토크온라인 밋업

Transcript

1. ա੄
   ೐۽Ӓې߁
   ࠽۠
   ੼ࣻח زܐٜ ّݾ ੟ѱ ݅٘ח աࢂ ೐۽Ӓې߁ णҙ ࠘ష௼ ৡۄੋ 2020.04.18 ߓ೙઱
2. द੘ೞӝ જ਷
   ೐۽Ӓې߁੉ۆ ▸ ߸ࣻ ੉ܴਸ ૙ח ؘ о੢ જ਷ ߑߨ਷ ޖ঺ੑפө? ▸ ࢲ࠳ܖ౯ਸ ࢎਊೞח ؘ যו ੿ب੄ ࠂ੟بө૑ ೲਊ೧ঠ ೤פө? ▸ ௿ېझܳ ੿੄ೞח ؘ ୭؀ ݻ ઴ ө૑ ೲਊ೧ঠ ೤פө? ▸ ঴݃ա ݆਷ ௏٘о పझ౟ غযঠ ೤פө?
3. द੘ೞӝ
4. ױ
   ೞա੄
   ઱ࢳب
   হ੉
   ѐߊਸ
   ೧ب
   ؾפө
   ૑৉
   ߸ࣻࠁ׮
   ੹৉
   ߸ࣻܳ
   ࢶഐ೧ب
   ؾפө
   ನੋఠо
   OVMMੋ
   ҃਋
   ੉
   чਸ
   ഛੋೞ૑
   ঋইب
   ؾפө য়ט੄
   ݾ಴
   
   द੘ೞӝ NO!
5. WARMING UP చҗ
   ڸযॳӝ ▸ ׮਺ ௏٘ীࢲ a= -10 ੌٸ, number ੄ ч਷? public class Main { } 2. Number = -10 1. Number = 0 public int number; public void assignIfPositive(int a) { } if(a > 0) number = a; System.out.println("a is positive"); ௏٘ח ׮ܲ ࢎۈҗ ੄ࢎࣗా ೞח ୐ߣ૩ ࣻױ੉׮. 2. Number = -10
6. ҳࢿҗ ҳઑ લ਷
   ௏٘ ▸ ׮਺ ௏٘੄ Ѿҗ ч਷? public void doProcessRandomly() { double n = Math.random(); if (n > 10) { System.out.println("n is over 10"); } else { System.out.println("n is " + n); } } 2. N is over 10 1. N is 0.15.. 3. Random ل ઺ ೞա 1. N is 0.15.. ▸ Math.random() ೣࣻח 0җ 1ࢎ੉੄ чਸ ߈ജೠ׮. // if ղ੄ ௏٘ח ੺؀ प೯ ؼ ࣻ হח લ਷ ௏٘׮. double n = GdgUtils.getRandomValue(); ▸ ழझథ ೣࣻо ٜযр׮ݶ? ࠛ೙ਃೠ ௏٘ח ૑ਕ઱੗
7. ҳࢿҗ ҳઑ ▸ ׮਺ ௏٘ী ࣻ੿੘স੉ ٜয৳णפ׮. Price < 0 ੌ ٸ, “੤ੑҊ ৘੿” ਵ۽ ߄Լ઱ࣁਃ. /** * ݅ড price о 0 ࠁ׮ ੘ਵݶ ಿ੺ਸ ୹۱ೠ׮. * @param price оѺ */ public void displayPrice(int price) { String message; if(price < 0) { message = "ಿ੺"; } else { message = price + "ਗ"; } System.out.println(message); } “੤ੑҊ ৘੿";
8. ҳࢿҗ ҳઑ সؘ੉౟
   غ૑
   ঋই
   पઁ
   ೯زҗ
   ੌ஖ೞ૑
   ঋח
   ઱ࢳ ▸ Price чਸ ୹۱೧ ࠇद׮. જ਷ ઱ࢳ਷ ௏٘ܳ ݺഛೞѱ ೞҊ Ӓ ٍী ऀ਷ ੄޷ܳ ࢸݺೠ׮ Main.display..
9. ߸ࣻ ബਯ੸ੋ
   ߸ࣻ
   ࢶ঱ ▸ Bobҗ John੄ Score ח? int scoreBob, 1. scoreBob = 10, scoreJohn = 10 2. scoreBob = 0, scoreJohn = 10 2. scoreBob = 0, scoreJohn = 10 https://www.oracle.com/technetwork/java/javase/documentation/codeconventions-141270.html#2992 ೠ ઴ীח ೞա੄ ߸ࣻ݅ ࢶ঱ೞ੗. scoreJohn = 10; int
10. ߸ࣻ ఋੑ
    ୓҅ܳ
    ৮੹൤
    ঈਊೞӝ int status_code = connect_to_device(); switch (status_code) { case 0: display_info(info_message[1]); break; case 1: reattempt(); break; case 2: display_warning(warning_messages[3]); break; } ▸ status_code == 1 ࢚క ч਷? ী۞௏٘ࠁ׮ח ৘৻о ੌ߈੸ਵ۽ ӂ੢ػ׮. // ???
11. ߸ࣻ DeviceStatus status = connect_to_device(); switch (status) { case SUCCESS: display_info(info_message.CONNECTION_SUCCEEDED); break; case ERROR_NO_PINGBACK: reattempt(); break; case WARNING_CONNECTION_SLOW: display_warning(warning_messages.CONNECTION_SLOW); break; } ࢚క ௏٘ܳ ࢎਊೡ ٸח пп੄ ݫद૑о ޖ঺ਸ ׸Ҋ ੓ח૑ ݺഛ൤ ॄળ׮. public enum DeviceStatus { SUCCESS = 0, WARNING_CONNECTION_SLOW, ERROR_NO_PINGBACK }
12. ઑѤޙ ؀উ਷
    হ׮ ▸ ੼ࣻо 60੼ ੉࢚੉ۄݶ “Pass”ܳ ઱ࣁਃ. public void calculateGrade(int score) { if (score > 60) { grade = "Pass"; } ▸ ੼ࣻо 40੼ ੉ۄݶ? } else { grade = "Fail"; } } ▸ ੹ޙ੸ਵ۽ ੘ࢿػ ࣗ೐౟ਝয੄ if ޙ ઺ 50~80%ী else ੺੉ হ׮ח Ѫ੉ ߋഃ઎׮. (Elshoff, 1976) ৘࢚ оמೠ ч ৻ী ೦࢚ ݅ੌ੄ ࢎకܳ Ҋ۰ೞ੗.
13. ߈ࠂޙ ఎ୹਷
    ղ݋؀۽
    while(true) { //ୡ௒݁੉ۄݶ ղо ਗೞ؍ Ѫ੉׮! if (currentSnack.getType().equals("Chocolate")) { chosenSnack = currentSnack; break; } // Ӓۧ૑ ঋ׮ݶ Ӗܖబ੉ হח ࠺झఉਸ ࢶఖೞѷ׮! else if (currentSnack.getType().equals("Biscuit")) { boolean containGluten = hasGluten(currentSnack); if(!containGluten) { chosenSnack = currentSnack; break; } } // হਵݶ ׮਺ਵ۽ ֈযр׮. if (snackIterator.hasNext()) { currentSnack = snackIterator.next(); } else { break; } } for(int i = 0; chosenSnack == null && i < snacks.size(); i++) { chrrentSnack = snacks.get(i); switch(currentSnack.getType()) { case "Chocolate" : chosenSnack = currentSnack; break; case "Biscuit" : if(hasGluten(currentSnack)) { chosenSnack = currentSnack; } break; } } ▸ ৈ۞ ѐ੄ ߈ࠂ ઙܐ੼਷ ҃۽ܳ ࠂ੟ೞѱ ٜ݅Ҋ ௏٘ ੉೧ܳ য۵ѱ ݅ٚ׮. ೞա੄ ߈ࠂޙীח ೞա੄ ઙܐ੼݅ ك׮. ▸ break, continue, return
14. ࢲ࠳ܖ౯ ߈ജ
    чਸ
    о૑Ҋ
    ֥ইࠁ੗ ▸ ৖੄ ௏٘੄ Ѿҗ ч਷? void move(int x, int xDistance, int y, int yDistance) { x += xDistance; y += yDistance; } void recordMovement(int x, List<Integer> xs, int y, List<Integer> ys) { xs.add(x); ys.add(y); } void displayMoves() { int xPos = 5; int yPos = 5; List<Integer> xMoves = new ArrayList<>(); List<Integer> yMoves = new ArrayList<>(); System.out.println("X :" + xPos + ", Y :" + yPos); move(xPos, 10, yPos, -20); recordMovement(10, xMoves, -20, yMoves); System.out.println("X-Movements : " + xMoves); System.out.println("Y-Movements : " + yMoves); System.out.println("X :" + xPos + ", Y :" + yPos); } X : Y : X-Movements: Y-Movements: X : Y : 5 5 5 5 10 -20 ࢲ࠳ܖ౯੉ ߸ࣻܳ ࣻ੿೧ঠ ೠ׮ݶ ࢜۽਍ чਸ ٜ݅য ߈ജೞ੗.
15. ௿ېझ৬ ё୓ ਬোೞ૑
    ঋ਷
    ҙ҅ ▸ Ҋন੉ܳ ୶оೞח ௏٘ܳ ੘ࢿ೧ ઱ࣁਃ. public static void main(String[] args) { PetFeeder feeder = new PetFeeder(); Dog lassie = new Dog(); feeder.giveFood(lassie); class Cat { public void feed() { System.out.println("cat feed"); } } class PetFeeder { public void giveFood(Dog d) { d.feed(); } class Dog { public void feed() { System.out.println("dog feed"); } } ઱য૓ ௿ېझ } Cat felix = new Cat(); feeder.giveFood(felix); giveFood(felix); } public void giveFood(Cat c) { c.feed(); }
16. ௿ېझ৬ ё୓ ਬোೞ૑
    ঋ਷
    ҙ҅ ▸ Ҋন੉ܳ ୶оೞח ௏٘ܳ ੘ࢿ೧ ઱ࣁਃ. public static void main(String[] args) { PetFeeder feeder = new PetFeeder(); Dog lassie = new Dog(); feeder.giveFood(lassie); class Cat { public void feed() { System.out.println("cat feed"); } } class PetFeeder { public void giveFood(Dog d) { d.feed(); } public void giveFood(Cat c) { c.feed(); } } class Dog { public void feed() { System.out.println("dog feed"); } } ઱য૓ ௿ېझ } Cat felix = new Cat(); feeder.giveFood(felix); giveFood(felix); interface Pet { void feed(); } class PetFeeder { public void giveFood(Pet p) { p.feed(); } } implements Pet { implements Pet { ё୓૑ೱ ೐۽Ӓې߁੄ ࢸ҅ח ੋఠಕ੉झ ೐۽Ӓې߁ਸ ࢶഐೠ׮.
17. ݃ޖܻ ੿ܻೞӝ ▸ ௏٘ח ׮ܲ ࢎۈҗ ੄ࢎࣗా ೞח ୐ߣ૩ ࣻױ੉׮. ▸ ࠛ೙ਃೠ ௏٘ח ૑ਕ઱੗ ▸ જ਷ ઱ࢳ਷ ௏٘ܳ ݺഛೞѱ ೞҊ Ӓ ٍী ऀ਷ ੄޷ܳ ࢸݺೠ׮ ▸ ೠ ઴ীח ೞա੄ ߸ࣻ݅ ࢶ঱ೞ੗. ▸ ী۞௏٘ࠁ׮ח ৘৻о ੌ߈੸ਵ۽ ӂ੢ػ ׮. ▸ ࢚క ௏٘ܳ ࢎਊೡ ٸח пп੄ ݫद૑о ޖ঺ ਸ ׸Ҋ ੓ח૑ ݺഛ൤ ॄળ׮. ▸ ৘࢚ оמೠ ч ৻ী ೦࢚ ݅ੌ੄ ࢎకܳ Ҋ۰ ೞ੗. ▸ ೞա੄ ߈ࠂޙীח ೞա੄ ઙܐ੼݅ ك׮. ▸ ࢲ࠳ܖ౯੉ ߸ࣻܳ ࣻ੿೧ঠ ೠ׮ݶ ࢜۽਍ ч ਸ ٜ݅য ߈ജೞ੗. ▸ ё୓૑ೱ ೐۽Ӓې߁੄ ࢸ҅ח ੋఠಕ੉झ ೐ ۽Ӓې߁ਸ ࢶഐೠ׮.