一、代码

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

public class Main1 {


    public static void main(String[] args) {
        Date nowDate = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("aa", Locale.ENGLISH);
        String format = sdf.format(nowDate);
        System.out.println(format);
        if(format.contains("PM")){
            System.out.println("下午");
        }else if(format.contains("AM")){
            System.out.println("上午");
        }

        SimpleDateFormat sdf2 = new SimpleDateFormat("MMM dd,yyyy HH:mm:ss aa", Locale.ENGLISH);
        String format2 = sdf2.format(nowDate);
        System.out.println("24小时制："+format2);

        SimpleDateFormat sdf3 = new SimpleDateFormat("MMM dd,yyyy h:mm:ss aa", Locale.ENGLISH);
        String format3 = sdf3.format(nowDate);
        System.out.println("12小时制："+format3);

    }
}

二、输出