Trying to solve this using Streams API - java help on CodeGym

Hello guys! I was able to solve this task by using just an old fashioned 'if' and 'while' loop but I was thinking about approaching this issue differently but couldn't make it work. Could you please help me figure out what I should change in my code here to make it work and solve this task 0816 using Streams API? Thanks in advance :)

public static void removeAllSummerPeople(HashMap<String, Date> map) {
     Iterator<Map.Entry<String, Date>> iter = map.entrySet().iterator();
     Calendar cal = new GregorianCalendar();

     while (iter.hasNext()) {
         Map.Entry<String, Date> entry = iter.next();
         cal.setTime(entry.getValue());

          map.entrySet().removeIf(v -> v.getValue().getTime() == Calendar.JUNE
                                 || v.getValue().getTime() == Calendar.JULY
                                 || v.getValue().getTime() == Calendar.AUGUST);
     }
 }

I tried also another approach similar to my 'original' solution but without any luck:

map.entrySet().removeIf(v -> cal.get(Calendar.MONTH) == Calendar.JUNE
                                    || cal.get(Calendar.MONTH) == Calendar.JULY
                                    || cal.get(Calendar.MONTH) == Calendar.AUGUST);

I haven't mastered streams in Java yet so any help and any hints you might have are appreciated!

public static void removeAllSummerPeople(HashMap<String, Date> map) { map.entrySet().removeIf(v -> (v.getValue().getMonth() == Calendar.JUNE || v.getValue().getMonth() == Calendar.JULY || v.getValue().getMonth() == Calendar.AUGUST)); }

SimpleDateFormat format = new SimpleDateFormat("M"); map.entrySet().removeIf(v -> (Integer.parseInt(format.format(v.getValue())) - 1 == Calendar.JUNE || Integer.parseInt(format.format(v.getValue())) - 1 == Calendar.JULY || Integer.parseInt(format.format(v.getValue())) - 1 == Calendar.AUGUST));

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Nouser

Level 36 , Germany

15 November 2020, 09:15

solution

Problem 1: removeIf already iterates over the entire entry set. So if you surround that with an iterator you're allowed just to use that iterators methods to delete entries. But you have the additional removeIf... in case the check succeeds, you will probably get a concurrant modification exception. Problem 2: getTime returns a Date object, nothing that you can compare with that enum (that's an int). So cause the check will never succeed, you don't get the exception for problem 1 Here you are working with Date objects and as a quick hack you could use its deprecated method getMonth (that's an int) and compare that to the ints from the enum like:

But I have no clue if this will validate, you tell me ;)

Michał

Level 11 , Warsaw, Poland

15 November 2020, 13:22

Thanks Nouser, that works. However, what about using other, not deprecated methods like suggested:

Calendar.get(Calendar.MONTH)

15 November 2020, 14:36

useful

don't get missleaded by the usage of that Calendar enum. That's just constant values that you can use everywhere but you're still working with Date objects that are stored in the map. And you need to get the month as an int out of that objects. These you compare to Calendar.JUNE or int 5 (nothing else is Calendar.JUNE). So you could use eg. SimpleDateFormat to do that for you. As pattern you use M. With that pattern you format the Date object you get out of the map. The result is a string and that string again you need to parse to an int so you can compare in with 5-7. And don't forget to subtract 1 of the result or add 1 to the Calendar.JUNE to AUGUST In code that could look similar to: