java 日付を比較する

Calendar calendar = Calendar.getInstance();

calendar.compareTo(日付)
// 同じであれば「0」　後であれば「1」　先で「-1」が返ります。

import java.util.Calendar;

public class App {
    public static void main(String[] args) throws Exception {
        
        Calendar calendar1 = Calendar.getInstance();        
        calendar1.set(2023, 1, 1, 10, 10, 10);
    
        Calendar calendar2 = Calendar.getInstance();    
        calendar2.set(2022, 12, 31, 10, 10, 10);

        Calendar calendar3 = Calendar.getInstance();    
        calendar3.set(2023, 1, 1, 10, 10, 11);        
    
        System.out.println( calendar1.compareTo(calendar1) ); // 0
        System.out.println( calendar1.compareTo(calendar2) ); // 1
        System.out.println( calendar1.compareTo(calendar3) ); // -1

    }
}