public class TestDate {

    public static void main(String[] args) throws ParseException {

        String str = "2016-6-28 8:00:00";

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        //字符串转Date

        Date date = sdf.parse(str);

        //Date转字符串

        str = sdf.format(date);

        System.out.println(date);

        System.out.println(str);

    }

}

Tue Jun 28 08:00:00 CST 2016

2016-06-28 08:00:00

public class YesterdayCurrent {

    public static void main(String[] args){

        Calendar cal = Calendar.getInstance();

        cal.add(Calendar.DATE, -1);

        System.out.println(cal.getTime());

    }

}