[Java] 명품 Java Programming 6장 연습 문제 풀이 해설 (실습 문제)

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[정답]

import java.util.Objects;

class MyPoint {
    private int x, y;

    public MyPoint(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public String toString() {
        return "Point (" + x + ", " + y + ")";
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof MyPoint) {
            MyPoint p = (MyPoint) obj;
            return this.x == p.x && this.y == p.y;
        }
        return false;
    }
}
public class DaraSolution {
    public static void main(String[] args) {
        MyPoint p = new MyPoint(3, 50);
        MyPoint q = new MyPoint(4, 50);
        System.out.println(p);

        if (p.equals(q)) {
            System.out.println("같은 점");
        } else {
            System.out.println("다른 점");
        }
    }
}

 

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[정답]

import java.util.Objects;

class Circle {
    private int x, y;
    private int radius;

    public Circle(int x, int y, int radius) {
        this.x = x;
        this.y = y;
        this.radius = radius;
    }

    @Override
    public String toString() {
        return "Circle(" + x + ", " + y + ") 반지름 " + radius;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj instanceof Circle) {
            Circle c = (Circle) obj;
            return x == c.x && y == c.y && radius == c.radius;
        }
        return false;
    }
}

public class DaraSolution {
    public static void main(String[] args) {
        Circle a = new Circle(2, 3, 5);
        Circle b = new Circle(2, 3, 50);
        System.out.println("원 a: " + a);
        System.out.println("원 b: " + a);

        if (a.equals(b)) {
            System.out.println("같은 원");
        } else {
            System.out.println("서로 다른 원");
        }
    }
}

 

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[정답]

package etc;

public class Calc {
	private int x, y;
	public Calc(int x, int y) { this.x = x; this.y = y; }
	public int sum() { return x+y; }
}

package main;
import etc.Calc;

public class MainApp {
	public static void main(String[] args) {
		Calc c = new Calc(10, 20);
		System.out.println(c.sum());
	}
}

 

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[정답]

package base;

public class Shape {
	public void draw() { System.out.println("Shape"); }
}

package derived;

import base.Shape;

public class Circle extends Shape {
	public void draw() { System.out.println("Circle"); }
}

package app;

import base.Shape;
import derived.Circle;

public class GraphicEditor {
	public static void main(String[] args) {
		Shape shape = new Circle();
		shape.draw();
	}
}

 

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[정답]

import java.util.Calendar;

public class DaraSolution {
	public static void main(String[] args) {
		Calendar now = Calendar.getInstance();
		
		int hourOfDay = now.get(Calendar.HOUR_OF_DAY);
		
		if(4<=hourOfDay && hourOfDay<12)
			System.out.println("Good Morning");
		else if(12<=hourOfDay && hourOfDay<18)
			System.out.println("Good Afternoon");
		else if(18<=hourOfDay && hourOfDay<22)
			System.out.println("Good Evening");
		else
			System.out.println("Good Night");
	}
}

 

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[정답]

import java.util.Scanner;

class Player {
    private String name;
    private long elapsedTime;

    Player(String name) {
        this.name = name;
        this.elapsedTime = 0;
    }

    String getName() {
        return name;
    }

    void setElapsedTime(long elapsedTime) {
        this.elapsedTime = elapsedTime;
    }

    long getElapsedTime() {
        return elapsedTime;
    }
}

class StopWatch {
    private long startTime;

    void start() {
        startTime = System.currentTimeMillis();
    }

    long stop() {
        return (System.currentTimeMillis() - startTime) / 1000;
    }
}

class TimeGame {
    private Player player1;
    private Player player2;
    private StopWatch stopWatch;

    TimeGame(Player player1, Player player2) {
        this.player1 = player1;
        this.player2 = player2;
        this.stopWatch = new StopWatch();
    }

    void playGame() {
        Scanner scanner = new Scanner(System.in);

        System.out.println("10초에 가까운 사람이 이기는 게임입니다.");

        // Player 1
        System.out.println(player1.getName() + " 시작 <Enter>키 >>");
        scanner.nextLine();
        stopWatch.start();
        System.out.println("현재 초 시간 = " + (System.currentTimeMillis() / 1000 % 60));
        System.out.println("10초 예상후 <Enter>키 >>");
        scanner.nextLine();
        long player1ElapsedTime = stopWatch.stop();
        player1.setElapsedTime(player1ElapsedTime);
        System.out.println("현재 초 시간 = " + (System.currentTimeMillis() / 1000 % 60));

        // Player 2
        System.out.println(player2.getName() + " 시작 <Enter>키 >>");
        scanner.nextLine();
        stopWatch.start();
        System.out.println("현재 초 시간 = " + (System.currentTimeMillis() / 1000 % 60));
        System.out.print("10초 예상후 <Enter>키 >>");
        scanner.nextLine();
        long player2ElapsedTime = stopWatch.stop();
        player2.setElapsedTime(player2ElapsedTime);
        System.out.println("현재 초 시간 = " + (System.currentTimeMillis() / 1000 % 60));

        // Show results
        System.out.println(player1.getName() + "의 결과 " + player1.getElapsedTime() + "초, " +
                player2.getName() + "의 결과 " + player2.getElapsedTime() + 
                	"초, 승자는 " + decideWinner().getName());
    }

    Player decideWinner() {
        long targetTime = 10; // 10 seconds

        long player1Difference = Math.abs(targetTime - player1.getElapsedTime());
        long player2Difference = Math.abs(targetTime - player2.getElapsedTime());

        if (player1Difference < player2Difference) {
            return player1;
        } else {
            return player2;
        }
    }
}

public class DaraSolution {
    public static void main(String[] args) {
        Player player1 = new Player("황기태");
        Player player2 = new Player("이재문");
        TimeGame timeGame = new TimeGame(player1, player2);
        timeGame.playGame();
    }
}

 

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[정답]

import java.util.Scanner;

public class DaraSolution {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.print(">> ");
            String input = scanner.nextLine();
            if (input.equals("그만")) {
                System.out.println("종료합니다...");
                break;
            }
            String[] words = input.split(" ");
            System.out.println("어절 개수는 " + words.length);
        }
        scanner.close();
    }
}

 

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[정답]

import java.util.Scanner;

public class DaraSolution {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("문자열을 입력하세요. 빈칸이 있어도 되고 영어 한글 모두 됩니다.");
        String str = scanner.nextLine();

        // 문자열의 길이만큼 반복
        for (int i = 0; i < str.length(); i++) {
            String rotated = str.substring(i) + str.substring(0, i);
            System.out.println(rotated);
        }
    }
}

 

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[정답]

import java.util.Scanner;

public class DaraSolution {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("가위바위보 게임입니다.");
        System.out.print("철수[가위(1), 바위(2), 보(3), 끝내기(4)]>>");
        int user = scanner.nextInt();
        int computer = (int) (Math.random() * 3) + 1;

        // 가위바위보 결과 출력
        while (true) {
            if (user == 4) {
                System.out.println("게임을 종료합니다...");
                break;
            }

            if (user < 1 || user > 4) {
                System.out.println("잘못 입력하셨습니다. 다시 입력해주세요.");
                System.out.print("철수[가위(1), 바위(2), 보(3), 끝내기(4)]>> ");
                user = scanner.nextInt();
                continue;
            }

            if (user == 1) {
                System.out.print("철수: 가위, ");
            } else if (user == 2) {
                System.out.print("철수: 바위, ");
            } else if (user == 3) {
                System.out.print("철수: 보, ");
            }

            if (computer == 1) {
                System.out.println("컴퓨터: 가위");
            } else if (computer == 2) {
                System.out.println("컴퓨터: 바위");
            } else if (computer == 3) {
                System.out.println("컴퓨터: 보");
            }

            // 가위바위보 결과 판별
            if (user == computer) {
                System.out.println("비겼습니다.");
            } else if ((user == 1 && computer == 3) ||
            	(user == 2 && computer == 1) || (user == 3 && computer == 2)) {
                System.out.println("철수가 이겼습니다.");
            } else {
                System.out.println("컴퓨터가 이겼습니다.");
            }

            System.out.print("철수[가위(1), 바위(2), 보(3), 끝내기(4)]>>");
            user = scanner.nextInt();
            computer = (int) (Math.random() * 3) + 1;
        }
    }
}

 

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[정답]

import java.util.Scanner;

class Person {
    private String name;

    public Person(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

class GamblingGame {
    private Person p1, p2;

    public GamblingGame(String name1, String name2) {
        p1 = new Person(name1);
        p2 = new Person(name2);
    }

    public void startGame() {
        Scanner scanner = new Scanner(System.in);

        while (true) {
            System.out.print("[" + p1.getName() + "]: <Enter> 키 >>");
            scanner.nextLine();
            int num1 = (int) (Math.random() * 3) + 1;
            int num2 = (int) (Math.random() * 3) + 1;
            int num3 = (int) (Math.random() * 3) + 1;
            System.out.println("\t" + num1 + " " + num2 + " " + num3);

            System.out.print("[" + p2.getName() + "]: <Enter> 키 >>");
            scanner.nextLine();
            int num4 = (int) (Math.random() * 3) + 1;
            int num5 = (int) (Math.random() * 3) + 1;
            int num6 = (int) (Math.random() * 3) + 1;
            System.out.println("\t" + num4 + " " + num5 + " " + num6);

            if (num1 == num2 && num2 == num3) {
                System.out.println(p1.getName() + "님이 이겼습니다!");
                break;
            } else if (num4 == num5 && num5 == num6) {
                System.out.println(p2.getName() + "님이 이겼습니다!");
                break;
            } else {
                System.out.println("아쉽군요!");
            }
        }
    }
}

public class DaraSolution {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("1번째 선수 이름>> ");
        String name1 = scanner.next();
        System.out.print("2번째 선수 이름>> ");
        String name2 = scanner.next();

        GamblingGame game = new GamblingGame(name1, name2);
        game.startGame();

        scanner.close();
    }
}

 

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[정답]

import java.util.Scanner;

public class DaraSolution {
    public static void main(String[] args) {
        // 문자열 입력받기
        Scanner scanner = new Scanner(System.in);
        System.out.print(">>");
        StringBuffer text = new StringBuffer(scanner.nextLine());

        while (true) {
            // 명령어 입력받기
            System.out.print("명령 : ");
            String command = scanner.nextLine();

            if (command.equals("그만")) {
                System.out.println("종료합니다.");
                break;
            } else if (command.contains("!")) {
                // 명령어 처리
                String[] parts = command.split("!");
                if (parts.length == 2) {
                    String target = parts[0];
                    String replacement = parts[1];
                    int index = text.indexOf(target);
                    // 문자열 치환
                    if (index != -1) {
                        text.replace(index, index + target.length(), replacement);
                    } else {
                        System.out.println("찾을 수 없습니다!");
                    }
                } else {
                    System.out.println("잘못된 명령입니다!");
                }
            } else {
                System.out.println("잘못된 명령입니다!");
            }

            System.out.println(text);
        }
    }
}

 

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[정답]

import java.util.Scanner;

class Person {
    private String name;

    public Person(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

class GamblingGame {
    private Person[] players;

    public GamblingGame(Person[] players) {
        this.players = players;
    }

    public void startGame() {
        Scanner scanner = new Scanner(System.in);

        while (true) {
            for (Person player : players) {
                System.out.print("[" + player.getName() + "]: <Enter> 키 >>");
                scanner.nextLine();
                int num1 = (int) (Math.random() * 3) + 1;
                int num2 = (int) (Math.random() * 3) + 1;
                int num3 = (int) (Math.random() * 3) + 1;
                System.out.println("\t" + num1 + " " + num2 + " " + num3);

                if (num1 == num2 && num2 == num3) {
                    System.out.println(player.getName() + "님이 이겼습니다!");
                    return;
                }
            }
            System.out.println("아쉽군요! 다시 시도하세요.");
        }
    }
}

public class DaraSolution {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("갬블링 게임에 참여한 선수 숫자>> ");
        int numPlayers = scanner.nextInt();
        scanner.nextLine();

        Person[] players = new Person[numPlayers];

        for (int i = 0; i < numPlayers; i++) {
            System.out.print((i + 1) + "번째 선수 이름>> ");
            String name = scanner.nextLine();
            players[i] = new Person(name);
        }

        GamblingGame game = new GamblingGame(players);
        game.startGame();

        scanner.close();
    }
}