Salut tous le monde !!!

Question sur la mission

Nous n'avons pas besoin de répétitions

Syntaxe Java, Niveau 8, Leçon 8

Discussion en cours

Where is the problem ?

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; /* Nous n'avons pas besoin de répétitions */ public class Solution { public static HashMap<String, String> creerMap() { HashMap<String, String> map = new HashMap<>(); map.put("Duroc", "théo"); map.put("Vigne", "théo"); map.put("Lemahieu", "fabrice"); map.put("Canet", "fabrice"); map.put("Perrin", "Christian"); map.put("Shwab", "Lisa"); map.put("Diawara", "Fatim"); map.put("Bouyeyia", "Meissan"); map.put("Gauthier", "Arnaud"); map.put("Mehus","Thomas"); return map; } public static void supprimerPrenonsIdentiques(Map<String, String> map) { HashMap<String, String> copie = new HashMap<>(map); int compte = 0; for (String prenomCopie : copie.values()) { for (String prenom : map.values()) { if (prenom.equals(prenomCopie)) { compte++; } } if (compte > 1) { supprimerElementMapParValeur(map, prenomCopie); compte = 0; } } } 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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Gellert Varga

niveau Szekesfehervar, Szekesfehervar, Hungary

16 septembre 2021, 16:17

And maybe a typing (misspelling) error: requirement says this is the name of the method: supprimerPrenomsIdentiques() but you use this name for method: supprimerPrenonsIdentiques()

Gellert Varga

niveau Szekesfehervar, Szekesfehervar, Hungary

16 septembre 2021, 16:11

I hope you tried out suggestion of Thomas. The problem is the handling of the 'compte' variable. You call the delete method when the compte is greater than 1. So when there are at least two matches. You do this well, because it only means repetition if you find equivalent "prenom" in the copied list more than 1 times. However, it is a problem that you only reset the compte to zero if it was greater than 1. It should be reset to zero even when it equals to 1! Because you start comparing a completely new item with all the items in the list. So when you find the first equivalent element in the copied list, compte++ ==2; and therefore you will call the delete method on that element, even though there is no repetition yet.

Thomas

niveau Bayreuth, Bayreuth, Germany

16 septembre 2021, 12:01

Why not add some code to main to test your newly written methods? Eg.:

Map<String, String> map = creerMap();
supprimerPrenonsIdentiques(map);
map.entrySet().forEach(System.out::println); // or just sout(map);

Gellert Varga

niveau Szekesfehervar, Szekesfehervar, Hungary

16 septembre 2021, 12:30

What this command means: System.out::println or what kind of operator are the two colons?

Thomas

niveau Bayreuth, Bayreuth, Germany

16 septembre 2021, 12:43

ahmmm.... that's a method reference and basically a short form for a lambda. That's why I edited the post and added // or just sout(map); In multithreading you'll read something about inner classes. And that's pretty much base knowledge for lambdas and then method references.

// method reference...
map.entrySet().forEach(System.out::println);
// is basically a short form of a lambda...
map.entrySet().forEach(entry -> System.out.println(entry));
// is a short form of a inner class
map.entrySet().forEach(new Consumer<Map.Entry<String, String>>() {
    @Override
    public void accept(Map.Entry<String, String> entry) {
        System.out.println(entry);
    }
});

with lambdas it is possible to save a lot of typing work like

map.forEach((k, v) -> System.out.println(k + " <---> " + v));
// for a method reference you need to write (or have) a signature similar method
// to the functional interface of the class used as parameter
// (basically there's passed a function and not a value anymore)
// (see below the inner class example)
// then the code is really easy to read and understand
map.forEach(Solution::printElement);


// the method that produces a similar result as the lambda
public static void printElement(String aKey, String aValue) {
    System.out.println(aKey + " <---> " + aValue);
}}

// and here again the same using a inner class, not really easy for the eye
map.forEach(new BiConsumer<String, String>() {
    @Override
    public void accept(String k, String v) {
        System.out.println(k + " <---> " + v);
});

this becomes really interesting if you want to work with the streams api

Gellert Varga

niveau Szekesfehervar, Szekesfehervar, Hungary

16 septembre 2021, 15:39

Thanks! It will come in handy one day when I understand more of these things. But now I have a faint idea about these things.:)