How to get the number of days in a week given a string date

Question

I have A string which is String dateOfOrder = "01/06/2019";

I would like to get the number of days in Week 1 as June first week only have 1 day.

May i know how do i approach on receviing number of days in Week X ?

Like In June 2019

Week 1 : Have 1 day Week 2 - 5 : have 7 days Week 6 : Have 1 day

EDIT

I'm thinking of this approach of getting number of days in a week whereby I have a couple of String arrayList. For example on my given date above, if Week 1 Have Saturday. Week 1 Array List will add saturday in it and .size(). If Week 2 have Sunday to Saturday, it will add all the dates in the Week 2 Array List and .size() to get the number of days in the ArrayList. Lastly, The last week of June which is Week 6 will have Sunday only and it will add into Week 6 ArrayList and have value of Sunday only and .size() to get 1.

I'm wondering if its the best approach and I'm not sure if i can get the correct days in the week.

Answer 1

Parse the string as date using SimpleDateFormatter . Your parsing pattern could be dd/MM/YYYY .

DateFormat df = new SimpleDateFormat("dd/MM/YYYY"); 
Date date = df.parse(dateOfOrder);

Once you have the date, get day of week using Calendar .

 Calendar c = Calendar.getInstance();
 c.setTime(yourDate);
 int dayOfWeek = c.get(Calendar.DAY_OF_WEEK);
 int dayOfMonth = c.get(Calendar.DAY_OF_MONTH);

Calculate number of days in the given week (and month).

int daysInMonth = c.getActualMaximum(Calendar.DAY_OF_MONTH);
int currentMonth = c.get(Calendar.MONTH);
int prevWeekMonth = c.add(Calendar.DAY_OF_MONTH, -7).get(Calendar.MONTH);

c.setTime(yourDate);
int nextWeekMonth = c.add(Calendar.DAY_OF_MONTH, 7).get(Calendar.MONTH);

c.setTime(yourDate);

if (prevWeekMonth != currentMonth) {
    // first or second week
    if (dayOfMonth > dayOfWeek) {
        // second week
        numOfDaysInWeek = 7;
    } else {
        // first week
        int firstDay = c.set(Calendar.DAY_OF_MONTH, 1).get(Calendar.DAY_OF_WEEK);
        numOfDaysInWeek = 7 - firstDay;
    }
} else if (nextWeekMonth != currentMonth) {
    // last or second last week
    if (dayOfMonth - dayOfWeek + 7 >= daysInMonth) {
         // last week
         numOfDaysInWeek = c.set(Calendar.DAY_OF_MONTH, daysInMonth).get(Calendar.DAY_OF_WEEK);
    } else {
         // second last week
         numOfDaysInWeek = 7;
    }
} else {
    // middle weeks
    numOfDaysInWeek = 7;
}

Note: the conditions are a bit rough and you might need to add 1 depending on whether dayOfWeek, dayOfMonth have 0 or 1 index.