【java】Date与String之间的转换及Calendar类：java.text.SimpleDateFormat、public Date parse(String source) throws ParseException和public final String format(Date date)

package 日期日历类;

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

public class TestDate {
    public static void main(String[] args) {
        Date date=new java.util.Date();
        System.out.println(date);//Fri Apr 07 22:20:12 CST 2017
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String d=sdf.format(date);
        System.out.println(d);//2017-04-07 22:20:12
        String d2="2017-04-06 12:30:30";
        Date date2=new Date();
        try {
            date2 = sdf.parse(d2);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        System.out.println(date2);//Thu Apr 06 12:30:30 CST 2017
    }
}

java.lang.Object
　　java.text.Format
　　　　java.text.DateFormat ->public Date parse(String source) throws ParseException和public final String format(Date date)
　　　　　　java.text.SimpleDateFormat

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package 日期日历类;

import java.util.Calendar;
import java.util.Date;

public class TestDate {
    public static void main(String[] args) {
        Date date=new java.util.Date();
        System.out.println(date);//Fri Apr 07 22:53:21 CST 2017
        Calendar cal=Calendar.getInstance();
        System.out.println(cal);//java.util.GregorianCalendar[time=1491576801409,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=19,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2017,MONTH=3,WEEK_OF_YEAR=14,WEEK_OF_MONTH=2,DAY_OF_MONTH=7,DAY_OF_YEAR=97,DAY_OF_WEEK=6,DAY_OF_WEEK_IN_MONTH=1,AM_PM=1,HOUR=10,HOUR_OF_DAY=22,MINUTE=53,SECOND=21,MILLISECOND=409,ZONE_OFFSET=28800000,DST_OFFSET=0]
        Date date2=cal.getTime();//Calendar转为Date
        System.out.println(date2);//Fri Apr 07 22:53:21 CST 2017
        StringBuffer sb=new StringBuffer();
        
        //月份从0开始算，所以要加1
        sb.append(cal.get(Calendar.YEAR)).append("年").append(cal.get(Calendar.MONTH)+1).append("月").append(cal.get(Calendar.DAY_OF_MONTH)).append("日").append(cal.get(Calendar.HOUR_OF_DAY)).append(":").append(cal.get(Calendar.MINUTE)).append(":").append(cal.get(Calendar.SECOND));
        System.out.println(sb);//2017年4月7日22:53:21
    }
}