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Je suis bloquée avec en plus une concurrentModificationException et je ne sais pas comment l'éviter. Quelqu'un pourrait il m'aider?

Crée une Map<String, String> et ajoute-lui dix entrées qui représentent des paires (nom, prénom).
Supprime les personnes ayant le même prénom.

Impératifs :

Le programme ne doit pas afficher de texte à l'écran.
Le programme ne doit pas lire de valeurs au clavier.
La méthode creerMap() doit créer et renvoyer une HashMap qui contient des éléments (String, String) et 10 entrées.
La méthode supprimerPrenomsIdentiques() doit supprimer de la Map toutes les personnes qui ont le même prénom.
La méthode supprimerPrenomsIdentiques() doit appeler la méthode supprimerElementMapParValeur().

package fr.codegym.task.task08.task0817; import java.util.HashMap; import java.util.Map; import java.util.Iterator; /* Nous n'avons pas besoin de répétitions */ public class Solution { public static HashMap<String, String> creerMap() { //écris ton code ici HashMap <String, String> identite = new HashMap<>(); identite.put("Lounes","Lilas"); identite.put("Kharbine","Luc"); identite.put("Poro","Jeanne"); identite.put("Jeannelle","Ludovic"); identite.put("Panco","Thierry"); identite.put("Sirop","Marie"); identite.put("Fillo","Lilas"); identite.put("Marcol","Therese"); identite.put("Filibert","Jean"); identite.put("Roche","Paul"); return identite; } public static void supprimerPrenomsIdentiques(Map<String, String> map) { //écris ton code ici HashMap<String, String> mapTemp = new HashMap<>(map); for(Map.Entry<String, String> entry : mapTemp.entrySet()){ //String valeur = map.keySet(); Iterator it = map.entrySet().iterator(); for(Map.Entry<String, String> personne : map.entrySet()) { if(entry.getValue().equals(personne.getValue())) { supprimerElementMapParValeur(map,personne.getValue()); } } } /*map.forEach((k,v) -> System.out.println("Key = " + k + ", Value = " + v)); */ } public static void supprimerElementMapParValeur(Map<String, String> map, String valeur) { HashMap<String, String> copie = new HashMap<String, String>(map); for (Map.Entry<String, String> paire : copie.entrySet()) { if (paire.getValue().equals(valeur)) map.remove(paire.getKey()); } } public static void main(String[] args) { } }

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Guadalupe Gagnon

niveau Tampa, Tampa, United States

28 août 2020, 14:16

It is illegal to continue iterating over a Collection, such as a map, with an Iterator or a foreach loop where an items was removed from that Collection. So: Line 36 creates a foreach loop on the Collection "map" Line 39, inside that foreach loop, removes items from "map" This is a direct violation of this principal and, as you have found out, will end up with a concurrent modification exception if the loop continues after an item is removed. With an Iterator, you can not remove items from the Collection that the Iterator was created on by using the remove() method of the iterator, however this task stipulates that you must use the method supprimerElementMapParValeur(). They do this so you are forced to deal with the exception, and this is an important topic to remember to avoid the pitfalls in the future. A couple tips: If you noticed I said it is a violation ONLY if the loop continues. You can remove items over a collection you are iterating over as long as the loop stops if that occurs. You could use this to solve the problem or There is nothing that says you can not loop over the same collection in nested loops. A quick visual of this: foreach loop over copy{ inner foreach loop over copy{ } } If you are only looping over the copy then it would be safe to remove items from the original. Now with your code, ignoring the illegal operation, it would remove every single item from "map". This is because if you make a copy of a Collection then line 38 would return true at least once for every value because every single value in map would also be in the copy of the map. You will need to change this logic so that it only removes items if there are more than one of the same item between the two maps.