24小时制时间显示:
public class Datetime {
    public static void main(String args[]){
         java.util.Date current=new java.util.Date();
           java.text.SimpleDateFormat sdf=new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); 
           String c=sdf.format(current);
           System.out.println(c);
    }
}
12小时制时间显示:
public class Datetime {
    public static void main(String args[]){
         java.util.Date current=new java.util.Date();
           java.text.SimpleDateFormat sdf=new java.text.SimpleDateFormat("yyyy-MM-dd hh:mm:ss"); 
           String c=sdf.format(current);
           System.out.println(c);
    }
}
两者区别:yyyy-MM-dd HH:mm:ss ;  yyyy-MM-dd hh:mm:ss