时间Date、Calendar

java.util  - Date  、 Calendar

java.text  Format  \  SimpleDateFormat  

import java.util.*;
import java.text.*;
public class Practice_1 {
    public static <K, V> void main(String[] args) {
        Date d = new Date();
        sop(d);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");
        String time =sdf.format(d);
        sop(time);
        
        
        
    }
    public static void sop(Object obj)
    {
        System.out.println(obj);
    }
}

输出结果： 

Fri Sep 06 15:26:55 CST 2019
2019年09月06日

Calendar 演示 ：

package CoreJavaPractice;

import java.util.*;
import java.text.*;

public class Practice_2 {

public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner in = new Scanner(System.in);
Calendar c = Calendar.getInstance();
sop("请输入年份:");
int year = in.nextInt();
c.set(year,2,1);
c.add(Calendar.DAY_OF_MONTH,-1);
sop(c);

sop(c.get(Calendar.YEAR)+ "年" );
sop((c.get(Calendar.MONTH)+1)+"月");
sop(c.get(Calendar.DAY_OF_MONTH)+"日");


sop("星期"+(c.get(Calendar.DAY_OF_WEEK)-1));

}
public static void sop(Object obj)
{
System.out.println(obj);
}

}