日期格式化问题

代码如下

sdf.format(date)将日期类型转为指定格式字符串

sdf.parse(str)将字符串类型转为Date类型

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.LinkedList;
import java.util.List;

	public class test {
	
	public static void main(String[] args) throws ParseException {
	List <Date> dates = new LinkedList<>();
	SimpleDateFormat sdf= new SimpleDateFormat("yyyy-mm-dd");
	
	String s1 = "2019-08-10 22:18:22";
	String s2 = "2018-08-10 22:18:22";
	String s3 = "2017-08-10 22:19:22";
	String s4 = "2025-01-10 22:19:22";
	String []s={s1,s2,s3,s4};
	//转日期
	dates.add(sdf.parse(s1));
	dates.add(sdf.parse(s2));
	dates.add(sdf.parse(s3));
	dates.add(sdf.parse(s4));
	//转日期，sdf.parse
	//转格式化，sdf.format
	//集合排序
//	Collections.sort(dates,(l,r)->{
//		return sdf.format(r).compareTo(sdf.format(l));
//	});
	
	
	//普通数组排序
//	Arrays.sort(s,(l,r)->{
//		return l.compareToIgnoreCase(r);
//	});
	
	//集合排序，直接倒置
	Collections.sort(dates,Comparator.reverseOrder());
	for(Date date:dates){
		System.out.println(sdf.format(date));
	}
	
	System.out.println(sdf.format(dates.get(0)).getClass());
	
//	dates.forEach(x->System.out.println(sdf.format(x)));
	

}

}

输出