Java Instance Calculate Duration between the Instant-CodePudding

public class Student {
    String firstName;
    String secondName;
    Instant lastClassAttendedOn;
}

Hi, I have been stuck on a problem where I have the list of students and I want to find out all the students who have attended at least one class in the previous week. By previous week, I mean from the previous week Monday to the previous week Friday as the school has a holiday on Saturday and Sunday. I might be checking the list any day of the week for example On Wednesday so I should get all the students who have taken at least a class in previous week

CodePudding user response：

As we are dealing with only days, it's sufficient to use LocalDate. Find out the start and end dates of the previous week from the current/ today's date. Then loop through the list and filter out the results from the start date.

LocalDate currentDate = LocalDate.now();

LocalDate start = currentDate.with(TemporalAdjusters.previous(DayOfWeek.MONDAY));
LocalDate end = currentDate.with(TemporalAdjusters.previous(DayOfWeek.FRIDAY));

for(Student student : studentsList) {
    Instant lastAccessedOn = student.getLastAccessedOn();
    LocalDate accessedDate = 
        lastAccessedOn.atZone(ZoneId.systemDefault()).toLocalDate();

    int noOfDays = start.until(accessedDate).getDays();
    if (noOfDays >= 0 && noOfDays <= 4) {
        // match found. Take this student
    }
}

Here, noOfDays may have negative values if the accessedDate lies in older weeks. So, check for >= 0. And we want to restrict till previous week's Friday. So it should be <= 4.