【Java】【19】Date Calendar相关

前言：发现开发过程当中要用到时间和日历的情况太多了，这里把我碰到的情况记录一下。

1，获取某月天数

2，获取两个日期之间的天数

3，查询当前日期前(后)x天的日期

4，获取某日期的前(后)N月的年月

5，周六周日判断

正文：

1，获取某月天数

public static int getMaxDay(int year, int month)
{
    Calendar cal = Calendar.getInstance(); //创建对象。不用new Calendar()的原因是Calendar是一个抽象类，且其构造方法是protected
    cal.clear();  //将所有字段值和时间值设置为未定义。Calendar类在set的时候，并不会立即生效，只有在get的时候才会生效，所以要先清理
    cal.set(Calendar.YEAR, year);
    cal.set(Calendar.MONTH, month-1); 
    
    return time.getActualMaximum(Calendar.DAY_OF_MONTH);
}

2，获取两个日期之间的天数

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//meiosisDate 减数
//minuendDate 被减数
public static int daysBetween(Date meiosisDate,Date minuendDate) throws ParseException    
{    
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Calendar cal = Calendar.getInstance(); 

    meiosisDate = sdf.parse(sdf.format(meiosisDate));       
    cal.setTime(meiosisDate);    
    long time1 = cal.getTimeInMillis();
    
    minuendDate = sdf.parse(sdf.format(minuendDate));
    cal.setTime(minuendDate);    
    long time2 = cal.getTimeInMillis(); 
    
    long between_days=(time1-time2)/(1000*3600*24);  
        
    return Integer.parseInt(String.valueOf(between_days));           
}

3，查询当前日期前(后)x天的日期

//查询当前日期前(后)x天的日期（如果day数为负数,说明是此日期前的天数）
public static String beforeNumberDay(int day) 
{
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Date now = new Date();
    Calendar c = Calendar.getInstance();
    c.setTime(now);
    c.add(Calendar.DAY_OF_YEAR, day);
    String theDate = sdf.format(c.getTime());
    
    return theDate;
}

4，获取某日期的前(后)N月的年月

//获取某日期的前(后)N月的年月
public static String yearMonthPrevNumber(String theDate, int num) throws ParseException
{
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
    Date date = sdf.parse(theDate);
    Calendar c = Calendar.getInstance();
    c.setTime(date);
    c.add(Calendar.MONTH, num);
    Date resultDate = c.getTime();

    String yearMonthPrevNumber = sdf.format(resultDate);
    
    return yearMonthPrevNumber;
}

5，周六周日判断

public static boolean isWeekend(Date date) 
{
    boolean isWeekend = false;            
    Calendar cal = Calendar.getInstance();
    cal.setTime(date);
    if (cal.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY
            || cal.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY) {
        isWeekend = true;
    }
    return isWeekend;
}