Date date = new Date();System.out.println(date);//Sun Mar 31 11:45:14 CST 2019
        Calendar calendar = Calendar.getInstance();System.out.println(calendar);//java.util.GregorianCalendar...//import java.sql.Timestamp;Timestamp timestamp = new Timestamp(System.currentTimeMillis());System.out.println(timestamp);//2019-03-31 11:45:14.512

    /*** * @param date1* @param date2* @return true-(date1早于date2)*/public static boolean compareDatetime(Date date1,Date date2) {boolean flag = false;//1/getTime()long aa = date2.getTime() - date1.getTime();if ( aa > 0 ) {flag = true;}//2/before()/after()flag = date1.before(date2);//3/compareTo()int bb = date2.compareTo(date1);System.out.println(bb);if ( bb > 0 ) {flag = true;}return flag;}

SimpleDateFormat sdf = new SimpleDateFormat("YYYY-MM-DD HH:mm:SS");
Date date = new Date();
String strDate = "";
//日期转字符串
strDate = sdf.format(date);
//字符串转日期
date = sdf.parse(strDate);

System.out.printf("%tF" + " " + "%tT", date1,date1);//2018-12-01 15:25:22

public static void main(String args[]) { try { long start = System.currentTimeMillis( ); System.out.println(new Date( ) + "\n");Thread.sleep(5*60*10); System.out.println(new Date( ) + "\n"); long end = System.currentTimeMillis( ); long diff = end - start; System.out.println("Difference is : " + diff); } catch (Exception e) { System.out.println("Got an exception!");} }

//创建一个代表2009年6月12日的Calendar对象
Calendar c1 = Calendar.getInstance();
//默认是当前日期
c1.set(2009, 6 - 1, 12);

Calendar c1 = Calendar.getInstance(); // c1 默认是当前日期
c1.add(Calendar.DATE, 1);//明天的日期
c1.add(Calendar.DATE, -1);//昨天的日期