只需结合YEAR属性检查DAY_OF_YEAR

boolean isSameDay = 
firstCal.get(Calendar.YEAR) == secondCal.get(Calendar.YEAR) &&
firstCal.get(Calendar.DAY_OF_YEAR) == secondCal.get(Calendar.DAY_OF_YEAR)

编辑:

现在我们可以使用Kotlin扩展函数的强大功能

fun Calendar.isSameDay(second: Calendar): Boolean {

    return this[Calendar.YEAR] == second[Calendar.YEAR] && this[Calendar.DAY_OF_YEAR] == second[Calendar.DAY_OF_YEAR]
}

fun Calendar.compareDatesOnly(other: Calendar): Int {

    return when {
        isSameDay(other) -> 0
        before(other) -> -1
        else -> 1
    }
}

Apache commons-lang几乎无处不在。那么这个呢?

if (DateUtils.isSameDay(date1, date2)) {
    // it's same
} else if (date1.before(date2)) {
   // it's before
} else {
   // it's after
}

已经提到了apache common -utils:

org.apache.commons.lang.time.DateUtils.truncate(date, Calendar.DAY_OF_MONTH)

给你Date对象，只包含日期，没有时间，你可以与Date. compareto进行比较

这里有一个来自这个博客的解决方案:http://brigitzblog.blogspot.com/2011/10/java-compare-dates.html

long milliseconds1 = calendar1.getTimeInMillis();
long milliseconds2 = calendar2.getTimeInMillis();
long diff = milliseconds2 - milliseconds1;
long diffDays = diff / (24 * 60 * 60 * 1000);
System.out.println("Time in days: " + diffDays  + " days.");

也就是说，你可以看到以毫秒为单位的时间差是否小于一天的长度。

使用SimpleDateFormat的getDateInstance，我们只能比较两个没有时间的日期对象。执行下面的代码。

public static void main(String[] args) {        
        Date date1  = new Date();
        Date date2  = new Date();
        DateFormat dfg = SimpleDateFormat.getDateInstance(DateFormat.DATE_FIELD);
        String dateDtr1 = dfg.format(date1);
        String dateDtr2 = dfg.format(date2);
        System.out.println(dateDtr1+" : "+dateDtr2);
        System.out.println(dateDtr1.equals(dateDtr2));  

    }

使用http://mvnrepository.com/artifact/commons-lang/commons-lang

Date date1 = new Date();

Date date2 = new Date();

if (DateUtils.truncatedCompareTo(date1, date2, Calendar.DAY_OF_MONTH) == 0)
    // TRUE
else
    // FALSE