Java 获取系统时间

1. Date类

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

2. System类

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

3. Calendar类

 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);

总结：系统时间可通过Date类、Calendar类和System中的currentTimeMillis来获取，时间格式可通过调用SimpleDateFormat类和String中的format方法来设置。