자바의 정석 - 남궁성

// Call By Value class Car { String color; } public class Test { public static void changeCarColor(Car car) { car.color = "Red"; // This change will reflect outside the method car = new Car(); // This will not reflect outside the method, because we're changing the reference, not the object it points to car.color = "Blue"; } public static void main(String[] args) { Car myCar = new Car(); myCar.color = "Green"; changeCarColor(myCar); System.out.println(myCar.color); // Prints "Red", not "Green" or "Blue" } }

#include <iostream> #include <string> struct Car { std::string color; }; void changeCarColor(Car*& car) { car->color = "Red"; // This change will reflect outside the function car = new Car(); // This change will also reflect outside the function car->color = "Blue"; } int main() { Car* myCar = new Car(); myCar->color = "Green"; changeCarColor(myCar); std::cout << myCar->color << std::endl; // Prints "Blue", not "Green" or "Red" delete myCar; return 0; }

List<Student> studentList = new ArrayList<>(); for (Student st : studentList) { // 생략 }

private ArrayList<Rental> _rentals = new ArrayList<Rental>(); Iterator<Rental> rentals = _rentals.iterator(); while (rentals.hasNext()) { // 생략 }

class CalculateArea { static int width = 10; static int height = 50; static int getArea (int a, int b) { return a * b; } }

interface Animal { public abstract void cry(); } interface Pet { public abstract void play(); } class Cat implements Animal, Pet { public void cry() { System.out.println("냐옹냐옹!"); } public void play() { System.out.println("쥐 잡기 놀이하자~!"); } }

class Box<T> { T item; void setItem(T item) { this.item = item; } T getItem() { return this.item; } } class Box { String item; void setItem(String item) { this.item = item; } String getItem() { return this.item; } } Box<String> b = new Box<>(); // 타입추론 기능에 따라 new 키워드 뒤에는 타입 생략 가능 b.setItem("ABC")

// 타입변수로 Fruit의 자식 클래스까지 받을 수 있음 class FruitBox<T extends Fruit> { ArrayList<T> list = ~~ }

interface Eatable {} class FruitBox<T extends Eatable> { ArrayList<T> list = ~~ }

class FruitBox<T> { static <T> void sort<List<T> list, ~~){ } }

static <T extends Fruit> Juice makeJuice(FruitBox<T> box) { // == static Juice makeJuice(FruitBox<T extends Fruit> box) return new Juice(); } FruitBox<Fruit> fruitBox = new FruitBox<Fruit>(); FruitBox<Apple> appleBox = new FruitBox<Apple>(); Juicer.<Fruit>makeJuice(fruitBox); // Juicer.makeJuice(fruitBox); Juicer.<Apple>makeJuice(appleBox); // Juicer.makeJuice(appleBox);

byte[] inScr = {0,1,2,3,4}; byte[] outScr = null; ByteArrayInputStream input = new ByteArrayInputStream(inScr); ByteArrayOutputStream output = new ByteArrayOutputStream(); int data = 0; // read(): 더이상 읽어올 데이터가 없으면 -1 반환 // -> data에 마지막으로 들어온 값이 -1이면 반복 중단 while((data = input.read()) != -1) { output.write(data); } // 스트림을 byte[]로 변환 outScr = output.toByteArray();

byte[] inScr = {0,1,2,3,4,5,,7,8,9}; byte[] outScr = null; byte[] temp = new byte[4]; ByteArrayInputStream input = new ByteArrayInputStream(inScr); ByteArrayOutputStream output = new ByteArrayOutputStream(); // available(): 스트림으로부터 읽어올 수 있는 데이터의 크기를 반환 while(input.available() > 0) { int len = input.read(temp); // 새롭게 입력받은 데이터의 수를 반환함 output.write(temp, 0, len); // 배열 temp에서 새롭게 입력 받은 데이터의 수만큼만 stream에 할당 } // 스트림을 byte[]로 변환 outScr = output.toByteArray();

try { FileOutputStream fileOutputStream = new FileOutputStream("123.txt"); // buffer의 크기를 5byte으로 지정함 BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream, 5); for(int i = '1'; i <= '9'; i++){ bufferedOutputStream.write(i); } bufferedOutputStream.close(); }catch (IOException e){ e.printStackTrace(); }

BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); String userId = br.readLine(); // Scanner scanner = new Scanner(System.in)); // String userId = scanner.nextLine()

public enum Operation { LIST, CREATE, UPDATE, REMOVE }

private Operation getOperationInput(String command) { Operation result = null; for (Operation operation : Operation.values()) { if (operation.toString().equalsIgnoreCase(command)) { result = operation; break; } } return result; }

System.out.println(1); try{ System.out.println(2); System.out.println(0/0); } catch (ArithmeticException e){ System.out.println(4); e.printStackTrace(); } System.out.println(5);

try { } catch (Exception | NullPointerException e) { // 에러 발생: Exception e로 간결하게 대체 가능 } try { } catch (NullPointerException | ClassCastException e) { // okay }

public void method() throws Exception1, Exception2 { // 내용 }

// getInstance 메소드는 static으로 사용 Calendar cal = Calendar.getInstance();

// Calendar -> Date Calendar cal = Calendar.getInstance(); Date d = new Date(cal.getTimeInMillis()); // Date -> Calendar Date d = new Date(); Calendar cal = Calendar.getInstance(); cal.setTime(d);

// 숫자 데이터 -> 특정 형식의 문자열 double number = 123456.89 DecimalFormat df = new DecimalFormat("#.#E0"); String result = df.format(number); // 특정 형식의 문자열 -> 숫자 데이터 Number num = df.parse("1.2E6");

Date today = new Date(); SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd"); String result = df.format(today);

String msg = "Name: {0} \nTel: {1} \nAge: {2} \nBirthDay: {3}"; Object[] arguments = { "배만진", "02-123-1234", "27", "07-09" }; String result = MessageFormat.format(msg, arguments);

final class Card { private Rank rank; private Suit suit; public Card(Rank rank, Suit suit) { this.rank = rank; this.suit = suit; } public boolean sameAs(Card anotherCard) { return rank.sameAs(anotherCard.rank) && suit.sameAs(anotherCard.suit); } }

final class ComplexNumber { private float realPart; private float complexPart; // create a new instance via static method public static ComplexNumber zero() { return new ComplexNumber(0, 0); } // create a new instance via constructor private ComplexNumber(float realPart, float complexPart) { this.realPart = realPart; this.complexPart = complexPart; } }

final class ComplexNumber { private float realPart; private float complexPart; // create a new instance via constructor public ComplexNumber(float realPart, float complexPart) { this.realPart = realPart; this.complexPart = complexPart; } // create a new ComplexNumber by addition public ComplexNumber add(ComplexNumber anotherComplexNumber) { return new ComplexNumber( realPart + anotherComplexNumber.realPart, complexPart + anotherComplexNumber.complexPart ); } // extract internal data and convert to String public String toString() { return String.format("%f + %f i", realPart, complexPart); } }

public class Age { private int value; private Age(int value) { this.value = value; validateValue(); } public static Age createAge(int value) { return new Age(value); } private void validateValue() { if (this.value < 1) { throw new IllegalArgumentException("1 이상의 값만 허용합니다"); } } }