How would I go about finding the closest date to a specified date? (Java)

I was hopi开发者_运维百科ng to know how I would type up a method to give me the closest date to a specified date. What I mean is something along the following:

public Date getNearestDate(List<Date> dates, Date currentDate) {
    return closestDate  // The date that is the closest to the currentDate;
}

I have found similar questions, but only one had a good answer and the code kept giving me NullPointerExceptions ... Can anyone help me?

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You can solve in linear time by computing the difference in time (e.g. Date#getTime()) and returning the minimum:

public static Date getNearestDate(List<Date> dates, Date currentDate) {
  long minDiff = -1, currentTime = currentDate.getTime();
  Date minDate = null;
  for (Date date : dates) {
    long diff = Math.abs(currentTime - date.getTime());
    if ((minDiff == -1) || (diff < minDiff)) {
      minDiff = diff;
      minDate = date;
    }
  }
  return minDate;
}

[Edit]

Minor performance improvements.

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Use Date#getTime and substract the values. The smallest result will be your closest date.

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Order the list by order of dates and perform a dichotomic search. Remember that to compare the dates you can use Date.getTime() to get the date as milliseconds, which are usually easier to compare.

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You would order the dates by the closest.

Have a start date set to 0:

long ret = 0;

Now you need to loop though your list and keep the closest to your desired date

for(Date d : dates){
    if(Math.abs(curDate.getTime() - ret) > Math.abs(curDate.getTime() - d.getTime())){
        ret = d.getTime();
    }
}
return new Date(ret);

The if statement checks which date is closer by comparing the millisecond time. By using Math.abs, you eliminate direction (before or after).