PLEASE HELP WHAT'S WRONG HERE

Question about the task

Kind Emma and the summer holidays

Java Syntax, Level 8, Lesson 8

Under discussion

I think everything's fine help me please im stuck : (

Create a Map<String, Date> and add ten entries that represent (last name, birth date) pairs.
Remove from the map all people born in the summer.
Hint: At CodeGym, summer lasts from June 1 to August 31.

Requirements:

The program should not display text on the screen.
The program should not read values from the keyboard.
The createMap() method must create and return a HashMap that has (String, Date) elements and contains 10 entries.
The removeAllSummerPeople() method should remove from the map all people born in the summer.

package com.codegym.task.task08.task0816; import java.text.DateFormat; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.HashMap; import java.util.Locale; import java.util.*; /* Kind Emma and the summer holidays */ public class Solution { public static HashMap<String, Date> createMap() throws ParseException { DateFormat df = new SimpleDateFormat("MMMMM d yyyy", Locale.ENGLISH); HashMap<String, Date> map = new HashMap<String, Date>(); map.put("Stallone", df.parse("JUNE 1 1980")); map.put("Sarah", df.parse("JUNE 1 1980")); map.put("Rejjie", df.parse("JUNE 1 1980")); map.put("Lance", df.parse("JUNE 1 1980")); map.put("Phoebe", df.parse("JUNE 1 1980")); map.put("Yumi", df.parse("JUNE 1 1980")); map.put("Nasty", df.parse("JUNE 1 1980")); map.put("Honey", df.parse("JUNE 1 1980")); map.put("Kris", df.parse("JUNE 1 1980")); map.put("Ched", df.parse("JUNE 1 1980")); //write your code here return map; //write your code here } public static void removeAllSummerPeople(HashMap<String, Date> map) { //write your code here HashMap<String, Date> map2 = new HashMap(map); for(Map.Entry<String, Date> elem: map.entrySet()){ String key = elem.getKey(); int month = elem.getValue().getMonth(); Date val = elem.getValue(); if(month == 6 || month == 7 || month == 8){ map2.put(key, val); } map = map2; } } public static void main(String[] args) { } }

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Nouser

Level 36 , Germany

27 March 2021, 13:46

Add also july and august born people and then check the content of your map with eg.

public static void main(String[] args) throws ParseException {
    HashMap<String, Date> map = createMap();
    removeAllSummerPeople(map);
    map.forEach((k, v) -> System.out.println(k + " <-> " + v));
}

and you'll see the problem

John

Level 17 , Mansfield, Philippines

27 March 2021, 14:32

oh i see, you use a lambda expression but can is solve this problem without lambda? coz im not familiar with it btw thank you :)

Nouser

Level 36 , Germany

27 March 2021, 14:47

It's just to output the map content after creating the map and calling removeAllSummerPeople. So it's not necessary to solve the task it just helps you to see where the problem is (if you add some more people as suggested above)

public static void main(String[] args) throws ParseException {
    HashMap<String, Date> map = createMap();
    removeAllSummerPeople(map);
    //map.forEach((k, v) -> System.out.println(k + " <-> " + v));
    for (Map.Entry<String, Date> element : map.entrySet())
        System.out.println(element.getKey() + " <->" + element.getValue());
}

John

Level 17 , Mansfield, Philippines

27 March 2021, 14:53

okay i get it, but still having a hardtime solving this :(

Nouser

Level 36 , Germany

27 March 2021, 15:31

you have two problems 1. Date numbers month from 0 - 11 2. map = map2; doesn't work as you think... map is a reference variable to the 'original' map. Now you just change the reference variable to point to the ne map. However that's just valid inside the removeAllSummerPeople method. In the main method the reference variable is still pointing to the original map. (Also in line 45, 46 you add summer people but you should remove them... but only if your actual approach would work, We change it and your conditions will perfectly fit). So you really need to remove the summer people from the original map, the map where the removeAllSummerPeople argument is pointing to. And that's not very difficult. Instead of iteration over the original map you iterate over the copy (map2).

for(Map.Entry<String, Date> elem: map2.entrySet()) {

Then you do not add elements but remove the found key from map

map.remove(key);

and make sure you change the condition to match months 5 - 7

if(month == 5 || month == 6 || month == 7) {

map = map2; you can safely delete (and in your original code you should have move it outside the loop)

John

Level 17 , Mansfield, Philippines

28 March 2021, 10:39

Thank you very Much Nouser!