Javaでシステム時刻を取得する方法

Date day=new Date();    
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); 
System.out.println(df.format(day));

SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");   
System.out.println(df.format(System.currentTimeMillis()));

Calendar c = Calendar.getInstance();//可以对每个时间域单独修改   
int year = c.get(Calendar.YEAR);  
 int month = c.get(Calendar.MONTH);   
int date = c.get(Calendar.DATE);    
int hour = c.get(Calendar.HOUR_OF_DAY);   
int minute = c.get(Calendar.MINUTE);   
int second = c.get(Calendar.SECOND);    
System.out.println(year + "/" + month + "/" + date + " " +hour + ":" +minute + ":" + second);

Date date = new Date();    
String year = String.format("%tY", date);   
String month = String.format("%tB", date);   
String day = String.format("%te", date);    
System.out.println("今天是："+year+"-"+month+"-"+day);