sort array list of special strings, by date

Question

I have an arrayList.

This is an arrayList of strings. The string contains a \"Date.toString\" in format of \"January 1, 1970, 00:00:00 GMT\" +

Answer 1

I would convert this array list first to something like

public class Event {
    private Date date;
    private String description;
    ...
}

After that, create a comparator to compare 2 events like this:

public class EventComparator implements Comparator<Event>{
    public int compare(Event e1, Event e2) {
        return e1.getDate().compareTo(e2.getDate());
    }
}

This will save you tons of performance compared with (pardon me) parsing each string for each comparison.

Answer 2

Write a comparator in which, convert the strings to dates for comparison. Collections.sort(List, Comparator); does the job after that.

Answer 3

Convert the array into a list of dates and then sort them:

List<Date> dates = new ArrayList<Date>();
for(String s : dateStringArray){
  // split the date and task name
  Pattern p = Pattern.compile("(\\w+ \\d{1,2}, \\d{4}, \\d{2}:\\d{2}:\\d{2} \\w{3})(.*)");
  Matcher matcher = p.matcher(s);
  String taskname = "";
  String datestring = "";
  if (matcher.find()) {
    datestring = matcher.group(1);
    taskname = matcher.group(2);
  }
  // parse the date
  Date d = new SimpleDateFormat("MMMM dd, yyyy, HH:mm:ss z", 
               Locale.ENGLISH).parse(datestring);
  dates.add(d);
}
// sort the dates
Collections.sort(dates);

If you want to keep the task names, you will have to make own objects that have the date and the task as fields and are comparable by the dates.

Answer 4

For each String, convert it to a Date, possibly using a SimpleDateFormat, and put them all in a TreeMap<Date,String>, which will sort them for you.

Edit: And as @Sean Patrick Floyd suggested, do it on input.

Answer 5

Write your own comparator. Then use Collections.sort(arrayList, myComparator);

Comparator<String> myComparator = new Comparator<String>() {

 int compareTo(String string1, String string2) {
     ......
 }

 boolean equals(String str1) {
    ......
 }

}

Answer 6

You could write a comparator that parses the dates and sorts them using date.compareTo(otherDate), but I'd suggest you store dates instead of Strings in the first place, making sorting much easier (Date implements Comparable<Date>.

(If your input format is String, then convert the Strings at the time you add them to the list)