java的Calendar类

阳光穿透心脏的1/2处 2022-08-21 15:56 182阅读 0赞

ava中的Calendar在开发中经常被忽略，这篇博客总结一下这个类，对后面项目中使用时期的时候有帮助。

## Calendar常量（field）的作用 ##

Calendar cal = Calendar.getInstance();
    cal.get(Calendar.DATE);//-----------------------当天 1-31
    cal.get(Calendar.DAY_OF_MONTH);//---------------当天 1-31
    cal.get(Calendar.DAY_OF_WEEK);//----------------从星期天开始计算，如果今天星期二，那么返回3
    cal.get(Calendar.DAY_OF_YEAR);//----------------
    cal.get(Calendar.HOUR);//-----------------------12小时制
    cal.get(Calendar.HOUR_OF_DAY);//----------------24小时制，一般使用这个属性赋值
    cal.get(Calendar.MILLISECOND);//----------------
    cal.get(Calendar.MINUTE);//---------------------
    cal.get(Calendar.SECOND);//---------------------
    cal.get(Calendar.WEEK_OF_MONTH);//--------------
    cal.get(Calendar.WEEK_OF_YEAR);//---------------
    cal.get(Calendar.MONTH);//-----------------------月份获取需要 +1，那么，赋值时需要 -1
    
    总结：
    1）常量的真正意义如上，我们一般使用这些常量进行赋值，换句话说，可以通过它获取值同样可以通过它进行对应赋值
    2）赋值时，week 与 month 是很值得注意的，week 需要指定 setFirstDayOfWeek ， 然而，月份则需要加减 1
    3）赋值时，我们一般采用 年 月 日 时 分 秒 
    Calendar.YEAR 、Calendar.MONTH 、Calendar.DAY_OF_MONTH、 Calendar.HOUR_OF_DAY 、Calendar.MINUTE、 Calendar.SECOND

## 主要赋值语句 ##

cal.set(Calendar.XXX, VVVV);//--------------------- 对以上每个字段（field）进行赋值，代码重复较大
     cal.set(year,month,date,hour,minute,second);//----- 分别对字段（field）进行赋值，效率高

## 主要计算 ##

cal1.roll(Calendar.MONTH,3);//---------------------- 一般不使用，原因是该方法只在一个月里面循环计算，其大小不会超过该月最值
     cal1.add(Calendar.YEAR,-1);//----------------------- 使用 XX_OF_XX 的field进行加减计算效果更佳，而且计算准确
     cal1.add(field,value);//----------------------------
    
    总结：
        1）关于roll的计算，cal.roll(Calendar.DAY_OF_MONTH, 32);虽然32已经超出了最大的可能31，但是cal实际是不会超出该月的，而是把32减去该月天数之后，重新计算剩下的天数；
        2）关于add的计算，cal1.add(Calendar.MONTH, 1); 如果当前为8-31，那么，加一个月的话就是9-30，这个才是真正的准确

## 主要取值语句 ##

cal.getMaximum(Calendar.DATE);
        cal.get(Calendar.DATE);
        cal.getMinimum(Calendar.DATE);
        cal.setTimeInMillis(cal.getTime().getTime());
        cal.setTimeInMillis(new Date().getTime());
    总结：
        1）获取最大值，最小值是很常用的方法
        2）获取毫秒数后，可以通过 1000*60*60 进行计算

## Calendar 获取当天\\当月\\当周 ##

<code class="hljs sql has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">// 当天
 public String getThisToday(){
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
 Calendar cal = Calendar.getInstance();
 cal.set(Calendar.HOUR_OF_DAY,0);
 cal.set(Calendar.MINUTE, 0);
 cal.set(Calendar.SECOND,0);
 String start = sdf.format(cal.getTime());
 cal.set(Calendar.HOUR_OF_DAY,23);
 cal.set(Calendar.MINUTE, 59);
 cal.set(Calendar.SECOND,59);
 String end = sdf.format(cal.getTime());
 return start+"|"+end;
 }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul>

<code class="hljs sql has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">// 本周
 public String getThisWeekDate(){
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
 Calendar ca = Calendar.getInstance();
 ca.setFirstDayOfWeek(Calendar.MONDAY);
 ca.set(Calendar.DAY_OF_WEEK,Calendar.SUNDAY);
 ca.set(ca.get(Calendar.YEAR), ca.get(Calendar.MONTH),ca.get(Calendar.DATE),23,59,59);
 String end = sdf.format(ca.getTime());
 ca.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
 ca.set(Calendar.HOUR_OF_DAY,0);
 ca.set(Calendar.MINUTE, 0);
 ca.set(Calendar.SECOND,0);
 String start = sdf.format(ca.getTime());
 return start+"|"+end;
 }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul>

<code class="hljs sql has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">//本月日期段
 public String getThisMonthDate(){
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
 Calendar cc2 = Calendar.getInstance();
 int maxMonthDay = cc2.getActualMaximum(Calendar.DAY_OF_MONTH);
 cc2.set(cc2.get(Calendar.YEAR), cc2.get(Calendar.MONTH),maxMonthDay,23,59,59);
 String end = sdf.format(cc2.getTime());
 cc2.set(cc2.get(Calendar.YEAR), cc2.get(Calendar.MONTH),1,0,0,0);
 String start = sdf.format(cc2.getTime());
 return start+"|"+end;
 }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>