Date 클래스 기본 사용법

import java.util.Date;

public class DateBasicExample {
    public static void main(String[] args) {
        Date current = new Date();
        Date future = new Date(current.getTime() + 1000);
        
        System.out.println("현재 시각: " + current);
        System.out.println("1초 후 시각: " + future);
    }
}

Calendar를 이용한 날짜 계산

import java.util.Calendar;

public class DateCalculationExample {
    public static void main(String[] args) {
        Calendar cal = Calendar.getInstance();
        cal.set(2023, Calendar.JANUARY, 15);
        cal.add(Calendar.DAY_OF_MONTH, 150);
        
        int year = cal.get(Calendar.YEAR);
        int month = cal.get(Calendar.MONTH) + 1;
        int day = cal.get(Calendar.DAY_OF_MONTH);
        
        System.out.println("계산된 날짜: " + year + "년 " + month + "월 " + day + "일");
    }
}

LocalDateTime과 날짜 포맷팅

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class DateTimeFormatExample {
    public static void main(String[] args) {
        LocalDateTime now = LocalDateTime.now();
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm");
        
        System.out.println("현재 날짜: " + now.toLocalDate());
        System.out.println("현재 시간: " + now.toLocalTime().withNano(0));
        System.out.println("포맷팅된 시간: " + now.format(formatter));
    }
}

현재 기준 날짜 계산

import java.util.Calendar;

public class FutureDateCalculator {
    public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.DATE, 100);
        
        int year = calendar.get(Calendar.YEAR);
        int month = calendar.get(Calendar.MONTH) + 1;
        int day = calendar.get(Calendar.DATE);
        
        System.out.printf("%d일 후 날짜: %d년 %d월 %d일", 100, year, month, day);
    }
}

특정 기간 일수 계산

import java.util.Calendar;

public class DaysSinceCalculator {
    public static void main(String[] args) {
        Calendar startDate = Calendar.getInstance();
        startDate.set(2000, Calendar.MARCH, 10);
        
        long startMillis = startDate.getTimeInMillis();
        long currentMillis = System.currentTimeMillis();
        long elapsedDays = (currentMillis - startMillis) / (1000 * 86400);
        
        System.out.println("경과 일수: " + elapsedDays);
    }
}