java编程中怎么获得当前系统的时间?

import java.util.Date;
import java.text.SimpleDateFormat;
public class NowString {
public static void main(String[] args) {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//设置日期格式
System.out.println(df.format(new Date()));// new Date()为获取当前系统时间
}
}

Date d = new Date();

import java.util.*;
public class Mydate{
public static void main(String[] args){
System.out.println(new Date());

}

}

package org.shao;

import java.util.Calendar;

public class Test1{

public static void main(String[] args) {

Calendar cld = Calendar.getInstance();
cld.add(Calendar.DATE, 0);
System.out.println(cld.getTime());

}
}