7. 메서드

/** * (현재 값 mod m) 값을 반환한다. 이 메서드는 항상 * 음이 아닌 BigInteger를 반환한다는 점에서 remainder 메서드와 다르다 * * @param m 계수(양수여야 한다.) * @return 현재 값 mod m * @throws ArithmeticException m이 0보다 작거나같을 경우 예외를 던진다. */ public BigInteger mod(BigInteger m) { if (m.signum() <= 0) { throw new ArithmeticException("계수(m)는 양수여야 합니다 " + m); } //... logic }

this.strategy = Objects.requireNonNull(strategy, "전략");

public static <T> T requireNonNull(T obj) { if (obj == null) throw new NullPointerException(); return obj; } public static <T> T requireNonNull(T obj, String message) { if (obj == null) throw new NullPointerException(message); return obj; }

private static void sort(long a[], int offset, int length){ assert a != null; assert offset >= 0 && offset <= a.length; assert length >= 0 && length <= a.length - offset; //... logics }

public static <T extends Comparable<? super T>> void sort(List<T> list) { list.sort(null); }

public class Product implements Comparable<Product>{ private long price; @Override public int compareTo(Product o) { // ClassCastException 발생 return (int)(this.price - o.price); } }

public class TestProduct { private String name; private String ip; private String port; private int num1; private int num2; private int num3; public TestProduct(String name, String ip, String port, int num1, int num2, int num3) { validateString(name, ip, port); valiateInteger(num1, num2, num3); this.name = name; this.ip = ip; this.port = port; this.num1 = num1; this.num2 = num2; this.num3 = num3; } private void valiateInteger(int... nums) { for (int num : nums) { if (num < 0 || num > 99) { throw new IllegalArgumentException("범위를 벗어났습니다."+num); } } } private void validateString(String... strings) { for (String str : strings) { if (str == null || str.startsWith("a") || str.endsWith("z")) { throw new IllegalArgumentException("유효하지 않은 값입니다." + str); } } } }

public final class Period { private final Date start; private final Date end; public Period(Date start, Date end) { if(start.compareTo(end) > ){ throw new IllegalArgumentException(start + "가" + end + "보다 늦다."); } this.start = start; this.end = end; } public Date start() { return start; } public Date end() { return end; } }

Date start = new Date(); Date end = new Date(); Period p = new Period(start, end); end.setYear(78); //p의 내부 수정이 가능하다.

public class LottoNumbers { private final List<LottoNumber> values = new ArrayList<>(); public LottoNumbers(List<LottoNumber> values){ this.values.addAll(values); } public List<LottoNumber> values() { return values; } } ... LottoNumbers ln = new LottoNumbers(Arrays.asList(n1, n2, n3, ... n)); ln.values().set(2, new LottoNumber(25)); ln.values().clear();

public Period(Date start, Date end) { this.start = new Date(start.getTime()); this.end = new Date(end.getTime()); if(start.compareTo(end) > ){ throw new IllegalArgumentException(start + "가" + end + "보다 늦다."); } public Date start() { return start; } public Date end() { return end; } }

public Date start() { return new Date(start.getTime()); } public Date end() { return new Date(end.getTime()); } ... public List<LottoNumber> values() { return new ArrayList<>(values); }

List<Integer> list = List.of(1,2,3,4,5,....N); //before list.searchOfRange(4, 14, 7); // start, end, target //after List<Integer> subList = list.subList(4, 14); int searchedIdx = subList.indexOf(7);

public PathResponse searchShortestPath(Long source, Long target) { checkEqualsStation(source, target); GraphPath resultPath = PathFinder.condition() .edgeList(lineRepository.findAll()) .vertexList(stationRepository.findAll()) .startStation(stationService.findById(source)) .endStation(stationService.findById(target)) .search(); List<Station> resultStations = resultPath.getVertexList(); List<StationResponse> stationResponses = resultStations.stream() .map(StationResponse::of) .collect(Collectors.toList()); return new PathResponse(stationResponses, resultPath.getWeight()); }

//before public void changeSwitch(boolean on) { if(on){ this.switch = "on"; onLight(); return; } this.switch = "off"; offLight(); } //after public enum SwitchType { ON, OFF } public void changeSwitch(SwitchType type){ if(SwitchType.ON.equals(type)){ this.switch = type; onLight(); return; } this.switch = type; offLight(); }

public enum TemperatureScale( FAHRENHEIT, CELSIUS } Thermometer.newInstance(true) Thermometer.newInstance(TemperatureScale.CELSIUS);

public class Main { public static class A {} public static class B extends A {} public static class C extends A {} public static class Classifier { public static String str(A a){ return "A"; } //---(1) public static String str(B b){ return "B"; } //---(2) public static String str(C c){ return "C"; } //---(3) } public static void main(String[] args){ A[] list = {new A(), new B(), new C()}; Stream.of(list) .map(it -> Classifier.str(it)) .forEach(System.out::println); } }

public class Main { public static class A { public String str(){ return "A"; } } public static class B extends A { @Override public String str() { return "B"; } } public static class C extends A { @Override public String str() { return "C"; } } public static void main(String[] args){ A[] list = {new A(), new B(), new C()}; Stream.of(list) .map(A::str) .forEach(System.out::println); } }

public class ObjectOutputStream extends OutputStream implements ObjectOutput, ObjectStreamConstants { public void writeBoolean(boolean val) throws IOException { bout.writeBoolean(val); } public void writeByte(int val) throws IOException { bout.writeByte(val); } public void writeShort(int val) throws IOException { bout.writeShort(val); } public void writeChar(int val) throws IOException { bout.writeChar(val); } //... logic }

public interface List<E> extends Collection<E> { //... logic boolean remove(Object o); E remove(int index); }

List<Integer> indexList = List.of(1,2,3,4,5); indexList.remove(3);

indexList.remove((Integer) 3);

new Thread(System.out::println).start(); ExecutorService exec = Executors.newCachedThreadPool(); exec.submit(System.out::println);

public boolean contentEquals(StringBuffer sb) { return contentEquals((CharSequence) sb); }

public void printArgs(String ... strs){ for(String str : strs){ System.out.println(str); } }

public void min(int... args){ if(args.length == 0){ throw new IllegalArgumentException(); } int min = args[0]; for(int arg : args){ if(arg < min){ min = arg; } } System.out.println(min); }

public void min(int firstArg, int... args){ int min = firstArg; for(int arg : args){ if(arg < min){ min = arg; } } System.out.println(min); }

public void method(){ ... } public void method(int a1){ ... } public void method(int a1, int a2){ ... } public void method(int a1, int a2, int a3){ ... } public void method(int a1, int a2, int a3, int... args){ ... }

public List<Cheese> getCheeses() { if(values.isEmpty()){ return null; } return new ArrayList<>(values); }

public void logic(){ List<Cheese> cheeses = shop.getCheese(); if(cheeses != null && cheeses.contains(Cheese.STILTON)){ System.out.println("exists Cheese"); } }

return new ArrayList<>(values);

public List<Cheese> getCheeses() { if(values.isEmpty()){ return Collections.emptyList(); } return new ArrayList<>(values); }

//default case public List<Cheese> getCheeses() { return values.toArray(new Cheese[0]); } //성능 최적화 private static final Cheese[] EMPTY_CHEESE_ARRAY = new Cheese[0]; public List<Cheese> getCheeses() { return values.toArray(EMPTY_CHEESE_ARRAY); }

//before public static <E extends Comparable<E>> E max(Collection<E> c) { if(c.isEmpty()){ throw new IllegalArgumentException(); } E result = null; for (E e C) { if(result == null || e.compareTo(result) > 0){ result = Objects.requireNonNull(e); } } return result; }

//after public static <E extends Comparable<E>> Optional<E> max(Collection<E> c) { if(c.isEmpty()){ return Optional.empty(); } E result = null; for (E e C) { if(result == null || e.compareTo(result) > 0){ result = Objects.requireNonNull(e); } } return Optional.of(result); }

//case 1. 기본값 설정 String lastWordInLexicon = max(words).orElse("단어 없음..."); //case 2. 예외 던지기 Toy myToy = max(toys).orElseThrow(TemperTantrumException::new);

public class NutritionalInformation { private final int calorie; //칼로리 - 필수 private final int sodium; //나트륨 private final int carbohydrate; //탄수화물 - 필수 private final int sugars; //당류 private final int fat; //지방 - 필수 private final int transFat; //트랜스지방 private final int saturatedFat; //포화지방 private final int cholesterol; //콜레스테롤 private final int protein; //단백질 - 필수 public NutritionalInformation() { this(0, 0, 0, 0, 0, 0, 0, 0, 0); } public NutritionalInformation(int calorie, int carbohydrate, int fat, int protein) { this(calorie, 0, carbohydrate, 0, fat, 0, 0, 0, protein); } public NutritionalInformation(int calorie, int sodium, int carbohydrate, int sugars, int fat, int transFat, int saturatedFat, int cholesterol, int protein) { this.calorie = calorie; this.sodium = sodium; this.carbohydrate = carbohydrate; this.sugars = sugars; this.fat = fat; this.transFat = transFat; this.saturatedFat = saturatedFat; this.cholesterol = cholesterol; this.protein = protein; } }

public interface List<E> extends Collection<E> { /** * Returns the element at the specified position in this list. * * @param index index of the element to return * @return the element at the specified position in this list * @throws IndexOutOfBoundsException if the index is out of range * ({@code index < 0 || index >= size()}) */ E get(int index); //method... }

/** * An instrument section of a symphony orchestra. */ public enum OrchestraSection { /** Woodwinds, such as flute, clarinet, and oboe. */ WOODWIND, /** Brass instruments, such as french horn and trumpet. */ BRASS, /** Percussion instruments, such as timpani and cymbals. */ PERCUSSION, /** Stringed instruments, such as violin and cello . */ STRING; }

/** * Indicates that the annotated method is a test method that * must throw the designated exceptionto pass. * (kor) 이 애너테이션이 달린 메서드는 명시한 예외를 던져야만 성공하는 * 테스트 메서드임을 나타낸다. */ @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface ExceptionTest { /** * The exception that the annotated test method must throw * in order to pass. (The test is permitted to throw any * subtype of the type described by this class object.) * (kor) 이 애너테이션을 단 테스트 메서드가 성공하려면 던져야 하는 예외. * (이 클래스의 하위 타입 예외는 모두 허용된다.) */ Class<? extends Throwable> value(); }

/** * Contains the collections framework, some internationalization support classes, * a service loader, properties, random number generation, string parsing * and scanning classes, base64 encoding and decoding, a bit array, and * several miscellaneous utility classes. This package also contains * legacy collection classes and legacy date and time classes. * * <h2><a id="CollectionsFramework"></a>{@index "Java Collections Framework"}</h2> * <p>For an overview, API outline, and design rationale, please see: * <ul> * <li><a href="doc-files/coll-index.html"> * <b>Collections Framework Documentation</b></a> * </ul> * * <p>For a tutorial and programming guide with examples of use * of the collections framework, please see: * <ul> * <li><a href="http://docs.oracle.com/javase/tutorial/collections/index.html"> * <b>Collections Framework Tutorial</b></a> * </ul> * * @since 1.0 */ package java.util;

/** * Defines JUnit Jupiter API for writing tests. */ module org.junit.jupiter.api { requires static transitive org.apiguardian.api; requires transitive org.junit.platform.commons; requires transitive org.opentest4j; exports org.junit.jupiter.api; exports org.junit.jupiter.api.condition; exports org.junit.jupiter.api.extension; exports org.junit.jupiter.api.function; exports org.junit.jupiter.api.io; exports org.junit.jupiter.api.parallel; opens org.junit.jupiter.api.condition to org.junit.platform.commons; }