如果你正在寻找一个简单的解决方案，但你不想从你的项目中更改已弃用的java.util.Date类，你可以将这个方法添加到你的项目中，并继续你的探索:

使用java.util.concurrent.TimeUnit

`

public boolean isSameDay(Date first, Date second) {
    long difference_In_Time = first.getTime() - second.getTime();
        // calculate difference in days
        long difference_In_Days = 
        TimeUnit
              .MILLISECONDS
              .toDays(difference_In_Time);
        if (difference_In_Days == 0) {
            return true;
        }
        return false;
    }

`

像这样实现它:

`

Date first = ...;
Date second = ...;
if (isSameDay(first, second)) {
    // congratulations, they are the same
}
else {
   // heads up champ, they are not the same
}

`

如果严格使用Date (java.util.Date)，或者不使用任何外部库。用这个:

public Boolean compareDateWithoutTime(Date d1, Date d2) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
    return sdf.format(d1).equals(sdf.format(d2));
}

我通过比较时间戳来解决这个问题:

    Calendar last = Calendar.getInstance();

    last.setTimeInMillis(firstTimeInMillis);

    Calendar current = Calendar.getInstance();

    if (last.get(Calendar.DAY_OF_MONTH) != current.get(Calendar.DAY_OF_MONTH)) {
        //not the same day
    }

我避免使用Joda Time，因为在Android上占用很大的空间。规模很重要。,)

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
    }
}

如果你只想比较两个没有时间的日期，那么下面的代码可能会帮助你:

final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
Date dLastUpdateDate = dateFormat.parse(20111116);
Date dCurrentDate = dateFormat.parse(dateFormat.format(new Date()));
if (dCurrentDate.after(dLastUpdateDate))
{
   add your logic
}

另一个简单的比较方法是基于这里的答案和我的导师的指导

public static int compare(Date d1, Date d2) {
    Calendar c1 = Calendar.getInstance();
    Calendar c2 = Calendar.getInstance();
    c1.setTime(d1);
    c1.set(Calendar.MILLISECOND, 0);
    c1.set(Calendar.SECOND, 0);
    c1.set(Calendar.MINUTE, 0);
    c1.set(Calendar.HOUR_OF_DAY, 0);
    c2.setTime(d2);
    c2.set(Calendar.MILLISECOND, 0);
    c2.set(Calendar.SECOND, 0);
    c2.set(Calendar.MINUTE, 0);
    c2.set(Calendar.HOUR_OF_DAY, 0);
    return c1.getTime().compareTo(c2.getTime());
  }

编辑: 根据@Jonathan Drapeau的说法，上面的代码在某些情况下会失败(我想看看这些情况)，他建议如下:

public static int compare2(Date d1, Date d2) {
    Calendar c1 = Calendar.getInstance();
    Calendar c2 = Calendar.getInstance();
    c1.clear();
    c2.clear();
    c1.set(Calendar.YEAR, d1.getYear());
    c1.set(Calendar.MONTH, d1.getMonth());
    c1.set(Calendar.DAY_OF_MONTH, d1.getDay());
    c2.set(Calendar.YEAR, d2.getYear());
    c2.set(Calendar.MONTH, d2.getMonth());
    c2.set(Calendar.DAY_OF_MONTH, d2.getDay());
    return c1.getTime().compareTo(c2.getTime());
}

请注意，Date类已弃用，因为它不适合国际化。取而代之的是Calendar类!