Java – the best way to find the date closest to the target in the date list?

I have a list of date objects and a target date I want to find the date closest to the target date in the list, but only the date before the target date

Example: October 1, 2008 October 2, 2008 October 4, 2008

The target date is October 3, 2008. I hope to get October 2, 2008

What is the best way?

Solution

The sietse de kaper solution assumes a reverse sort list, which is definitely not the most natural thing

The natural sort order in Java follows the ascending natural sort order (see collection.sort.) http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collections.html#sort (Java. Util. List) document)

From your example,

target date = 2008-10-03 
list = 2008-10-01 2008-10-02 2008-10-04 

If another developer uses your method in a naive way, he will get 2008-10-01, which is not expected

>Don't make assumptions about the order of the list. > If you have performance reasons, please try to follow the most natural Convention (sorted in ascending order) > if you really have to follow another convention, you really should record it

private Date getDateNearest(List<Date> dates,Date targetDate){
  Date returnDate = targetDate
  for (Date date : dates) {
    // if the current iteration'sdate is "before" the target date
    if (date.compareTo(targetDate) <= 0) {
      // if the current iteration's date is "after" the current return date
      if (date.compareTo(returnDate) > 0){
        returnDate=date;
      }
    }
  }  
  return returnDate;
}

Edit – I also like TreeSet's answer, but I think it may be a little slower because it is equivalent to sorting data and then finding it = > NLog (n) for sorting, and then the document implies that it is log (n) for access, so this will be NLog (n) log (n) vs n