Finding the intersection between two date ranges in Java (programatically)

Question

I would like to calculate the number of the overlapping days between two date ranges. The 2 pairs of date ranges are read from the console in the format: yyyy-mm-dd; For example, if the two dates are 2020-01-05 2020-03-31 and 2020-01-05 2020-03-20 the program should find the days between 2020-01-05 and 2020-03-20. However, it doesn't work. I would like to ask how can I fix this?

import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
import java.util.Scanner;

    public class Dates {
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            String a  = sc.nextLine();
            String b = sc.nextLine();
            String c  = sc.nextLine();
            String d = sc.nextLine();
            LocalDate ldt1 = LocalDate.parse(a);
            LocalDate ldt2 = LocalDate.parse(b);
            LocalDate ldt3 = LocalDate.parse(c);
            LocalDate ldt4 = LocalDate.parse(d);
            System.out.println(ChronoUnit.DAYS.between(ldt1,ldt2,ldt3,ldt4));
        }

    }

*"However, it doesn't work."* - What do you mean? Compilation errors? Runtime exceptions? Wrong answers? — Stephen C, Mar 21 '20 at 07:53

Ole V.V. · Accepted Answer · 2020-03-21T09:34:38.377

It’s a little more complicated than that (not badly).

    String i1StartStr = "2020-01-05";
    String i1EndStr = "2020-03-31";
    String i2StartStr = "2020-01-05";
    String i2EndStr = "2020-03-20";
    LocalDate i1Start = LocalDate.parse(i1StartStr);
    LocalDate i1End = LocalDate.parse(i1EndStr);
    LocalDate i2Start = LocalDate.parse(i2StartStr);
    LocalDate i2End = LocalDate.parse(i2EndStr);

    if (i1End.isBefore(i1Start) || i2End.isBefore(i2Start)) {
        System.out.println("Not proper intervals");
    } else {
        long numberOfOverlappingDates;
        if (i1End.isBefore(i2Start) || i2End.isBefore(i1Start)) {
            // no overlap
            numberOfOverlappingDates = 0;
        } else {
            LocalDate laterStart = Collections.max(Arrays.asList(i1Start, i2Start));
            LocalDate earlierEnd = Collections.min(Arrays.asList(i1End, i2End));
            numberOfOverlappingDates = ChronoUnit.DAYS.between(laterStart, earlierEnd);
        }
        System.out.println("" + numberOfOverlappingDates + " days of overlap");
    }

Output from the code as it stands here is:

75 days of overlap

I have also used better variable names and have introduced validation of the intervals that the user inputs.

I know I was supposed to add some explanation here, but frankly, I find the code using java.time so clear to read in itself, I don’t know what needs to be explained. If you want the number of days inclusive of both start and end dates, remember to add 1 to the return value from ChronoUnit.DAYS.between(). Please follow up in the comments and let me know what further explanation will be appropriate.

Finding the intersection between two date ranges in Java (programatically)

1 Answers1