如果你想要一行代码:

String date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(Calendar.getInstance().getTime());

结果是“2016-09-25 16:50:34”

String currentDateandTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
Toast.makeText(getApplicationContext(), currentDateandTime, Toast.LENGTH_SHORT).show();

为显示当前日期和时间的Textview

    /// For Show Date
    String currentDateString = DateFormat.getDateInstance().format(new Date());
    // textView is the TextView view that should display it
    textViewdate.setText(currentDateString);
    /// For Show Time
    String currentTimeString = DateFormat.getTimeInstance().format(new Date());
    // textView is the TextView view that should display it
    textViewtime.setText(currentTimeString);

检查完整的代码Android -显示当前日期和时间在一个Android Studio示例的源代码

String formattedDate = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(Calendar.getInstance().getTime()); 

使用formattedDate作为填充日期的字符串。 在我的情况下:mDateButton.setText(formattedDate);

Calendar c = Calendar.getInstance();
int month=c.get(Calendar.MONTH)+1;
String sDate = c.get(Calendar.YEAR) + "-" + month+ "-" + c.get(Calendar.DAY_OF_MONTH) +
"T" + c.get(Calendar.HOUR_OF_DAY)+":"+c.get(Calendar.MINUTE)+":"+c.get(Calendar.SECOND);

这将给出日期时间格式 2010 - 05 - 24 - t18:13:00

实际上，最好使用TextClock小部件。它为您处理所有的复杂性，并将尊重用户的12/24小时的偏好。 http://developer.android.com/reference/android/widget/TextClock.html