CODEWITHSUNDEEP
javastringstring-comparison
SnugglyCrow
SnugglyCrow

Reputation: 35

Comparing dates as strings in Java

I am having troubles comparing dates as strings. I am required to iterate through a collection and compare the date value of each object against 2 dates passed as parameters. The dates are all stored as strings and am required to keep them that way.

It is known that the dates will all be formatted YYYY-MM-DD. Below is a quick example of what I mean. Thanks all!

public ArrayList<Object> compareDates(String dateOne, String dateTwo) {
    for(Object object : objectCollection) {
        String objectDate = object.getDate();
        if(objectDate.equals(dateOne) || objectDate.equals(dateTwo)) { // Unsure of how to determine if the objects date is inbetween the two given dates
            //add object to collection
        }
    }
return  collection;
}

Upvotes: 2

Views: 5053

Answers (4)

Holmes
Holmes

Reputation: 406

Since your dates are in the YYYY-MM-DD format, a lexicographic comparison can be used to determine the ordering between two dates. Thus, you can just use the String.compareTo() method to compare the strings:

int c1 = objectDate.compareTo(dateOne);
int c2 = objectDate.compareTo(dateTwo);
if ((c1 >= 0 && c2 <= 0) || (c1 <= 0 && c2 >= 0)) {
    // objectDate between dateOne and dateTwo (inclusive)
}

If it is guaranteed that dateOne < dateTwo, then you can just use (c1 >= 0 && c2 <= 0). To exclude the date bounds, use strict inequalities (> and <).

Upvotes: 3

Bartek
Bartek

Reputation: 2219

If dateOne is before dateTwo you can use following comparison if you like have date inbetween.

    public ArrayList<Object> compareDates(List<Object> objectCollection, String start, String end) {
        ArrayList<Object> dateBetween = new ArrayList<>();
        for(Object object : objectCollection) {
            LocalDate objectDate = parseDate(object.getDate());
            if( !objectDate.isBefore(parseDate(start)) && !objectDate.isAfter(parseDate(end))) {
                dateBetween.add(object);
            }
        }
        return dateBetween;
    }

    private LocalDate parseDate(String date) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("YYYY-MM-DD");
        return LocalDate.parse(date, formatter);
    }

Upvotes: 0

Jude Niroshan
Jude Niroshan

Reputation: 4460

Here is the procedure you need to follow:

  1. Convert both String dateOne, String dateTwo into java.time.LocalDate

  2. Iterate over your ArrayList and convert the indexed string into java.time.LocalDate

    Note: You need to accept ArrayList<String> in order to parse the string to LocalDate, not ArrayList<Object>

  3. Do the comparison

Refer to the documentation to implement the comparison logic.

You may refer to this link for additional help.

Upvotes: 0

ernest_k
ernest_k

Reputation: 45319

As your dates are in the yyyy-MM-dd format, then String's compareTo should return consistent results:

if(objectDate.compareTo(dateOne) >= 0 && objectDate.compareTo(dateTwo) <= 0)

This roughly checks (conceptually): objectDate >= dateOne && objectdate <= dateTwo

That's just if one must use string's methods. A better approache, though, would be to convert the strings to date objects and perform a date-based comparisons.

Upvotes: 0

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