Android 格式化时间的几种方式，以下代码在 Android 6.0 API 23 上运行可用：

        // method 0 格式化当前时间
        String currentDateTimeString =
                new SimpleDateFormat("yyyy/MM/dd HH:mm:ss", Locale.US).format(new Date());

        // method 1 格式化当前时间
        currentDateTimeString =
                new SimpleDateFormat("yyyy/MM/dd HH:mm:ss", Locale.US).
                        format(Calendar.getInstance().getTime());

        // method 2 格式化当前时间
        Date date0 = new Date();
        CharSequence s = DateFormat.format("yyyy-MM-dd hh:mm:ss", date0.getTime());
        currentDateTimeString = String.valueOf(s);

        // method 3 格式化当前时间
        Calendar calendar = Calendar.getInstance();
        currentDateTimeString = calendar.get(Calendar.YEAR) + "/";
        currentDateTimeString += calendar.get(Calendar.MONTH) + 1 + "/";
        currentDateTimeString += calendar.get(Calendar.DAY_OF_MONTH) + " ";
        currentDateTimeString += calendar.get(Calendar.HOUR_OF_DAY) + ":";
        currentDateTimeString += calendar.get(Calendar.MINUTE) + ":";
        currentDateTimeString += calendar.get(Calendar.SECOND);

        // method 4 格式化指定时间，这里也是当前时间
        long time = System.currentTimeMillis();
        SimpleDateFormat format = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss", Locale.US);
        Date date1 = new Date(time);
        currentDateTimeString = format.format(date1);