1.字符串日期比较大小

    public static boolean compareDate(String pre, String last) {SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");try {Date lastDate = sdf.parse(last);Calendar lastCal = Calendar.getInstance();lastCal.setTime(lastDate);Date preDate = sdf.parse(pre);Calendar preCal = Calendar.getInstance();preCal.setTime(preDate);return preDate.after(lastDate);} catch (ParseException e) {e.printStackTrace();}return false;}

2.计算字符串日期相差多少天

    public static int getDays(String pre, String last) {SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");try {Date lastDate = sdf.parse(last);Calendar lastCal = Calendar.getInstance();lastCal.setTime(lastDate);Date preDate = sdf.parse(pre);Calendar preCal = Calendar.getInstance();preCal.setTime(preDate);long diff = lastCal.getTimeInMillis() - preCal.getTimeInMillis();float dayCount = (float) diff / (24 * 60 * 60 * 1000);return (int) dayCount;} catch (ParseException e) {e.printStackTrace();}return 0;}

3.获取上午、下午

    /**** 获取上午还是下午*/public static String getDateAmOrPm() {String nihao = "";Calendar cal = Calendar.getInstance();//测试代码//cal.set(Calendar.HOUR_OF_DAY, 15);if (cal.get(Calendar.AM_PM) == Calendar.AM) {nihao = "上午好";} else {nihao = "下午好";}return nihao;}

4.获取问好

    /**** 根据Calendar的hour来判断*/public static String getDateSx() {String nihao = "";Calendar cal = Calendar.getInstance();int hour = cal.get(Calendar.HOUR_OF_DAY);if (hour >= 6 && hour < 8) {System.out.println("早上好");nihao = "早上好";} else if (hour >= 8 && hour < 11) {System.out.print("上午好");nihao = "上午好";} else if (hour >= 11 && hour < 13) {System.out.print("中午好");nihao = "中午好";} else if (hour >= 13 && hour < 18) {System.out.print("下午好");nihao = "下午好";} else {System.out.print("晚上好");nihao = "晚上好";}return nihao;}

5.获取周几

    public static String[] weeks = new String[]{"周日", "周一", "周二", "周三", "周四", "周五", "周六"};public static String getWeekday() {Calendar calendar = Calendar.getInstance();String weekday = weeks[calendar.get(Calendar.DAY_OF_WEEK) - 1];return weekday;}

6.获取字符串年月日

    @RequiresApi(api = Build.VERSION_CODES.M)public static String convert(String dateString) {if (TextUtils.isEmpty(dateString)) return "";SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");try {Date date = format.parse(dateString);Calendar calendar = Calendar.getInstance();calendar.setTime(date);StringBuilder timestamp = new StringBuilder();timestamp.append(calendar.get(java.util.Calendar.YEAR) + "-");int month = calendar.get(java.util.Calendar.MONTH) + 1;if (month < 10) {timestamp.append("0" + month + "-");} else {timestamp.append(month + "-");}int day = calendar.get(java.util.Calendar.DAY_OF_MONTH);if (day < 10) {timestamp.append("0" + day);} else {timestamp.append(day + "");}return timestamp.toString();} catch (ParseException e) {e.printStackTrace();}return "";}

7.获取昨天

java.util.Calendar calendar = java.util.Calendar.getInstance();
calendar.add(java.util.Calendar.DAY_OF_MONTH, -1);