- java help on CodeGym

Magda

Poziom 10

Poland

15.02.2023
73widoki
3komentarze

Pytania dotyczące zadania

Tylko dla bogaczy

Składnia Java, Poziom 8, Lekcja 8

Dyskutowane

can't see what's wrong

Utwórz Map<String, Integer> i dodaj dziesięć wpisów, które odpowiadają parom (nazwisko, pensja).
Usuń z mapy wszystkie osoby, których pensja jest niższa niż 500.

Wymagania:

Program nie powinien wyświetlać tekstu na ekranie.
Program nie powinien czytać wartości z klawiatury.
Metoda utworzMap() powinna tworzyć i zwracać HashMap, która ma elementy (String, Integer) i zawiera 10 wpisów, które odpowiadają parom (nazwisko, pensja).
Metoda usunPozycjeZmap() musi usuwać z mapy wszystkie osoby, których pensja jest niższa niż 500.

package pl.codegym.task.task08.task0818; import java.util.HashMap; import java.util.*; /* Tylko dla bogaczy */ public class Solution { public static HashMap<String, Integer> utworzMap() { //tutaj wpisz swój kod HashMap<String, Integer> stIntHashMap = new HashMap<>(); stIntHashMap.put("Al", 5000); stIntHashMap.put("Al", 5000); stIntHashMap.put("Al", 5000); stIntHashMap.put("Al", 5000); stIntHashMap.put("Al", 5000); stIntHashMap.put("Mi0", 6); stIntHashMap.put("Mi0", 6); stIntHashMap.put("Mi0", 6); stIntHashMap.put("Mi0", 6); stIntHashMap.put("Mi0", 6); return (HashMap<String, Integer>) stIntHashMap; } public static void usunPozycjeZmap(HashMap<String, Integer> map) { //tutaj wpisz swój kod for(Integer x : map.values()) { if(x<500) { map.remove(x); } } } public static void main(String[] args) { } }

Komentarze (3)

Popularne
Najnowsze
Najstarsze

Musisz się zalogować, aby dodać komentarz

Magda

Poziom 10 , Poland, Poland

16 lutego, 18:15

HashMap<String, Integer> copy = new HashMap<String, Integer>(map); for (Map.Entry<String, Integer> pair : copy.entrySet()) but could you explain me what does the part with Map.Entry mean?

Thomas

Poziom 41 , Bayreuth, Germany

17 lutego, 09:05

When you add an entry to the map it has to be stored somewhere. The map is doing this the oop way and internally has a class for that the Entry. This Entry type can hold a key and a value. So when you want to iterate over a map you ask it to give you a set of all elements if holds. And these elements are of the type Entry (from outside the map you have to address it using Map.Entry). Map.Entry is generic. Means you can specify the stored types so it is type safe (Same as for List, Set...). So if you want to store LocalDateTime keys and String values inside a map, then you tell that the map with eg. new HashMap<LocalDateTime, String> and the hashmap internally creates Map.Entry<LocalDateTime, String> elements. So back to the start, you can ask for a set of all Entry elements inside the map using its method entrySet() and this method does exactly that and returns a set of Map.Entry<LocalDateTime, String> elements. Example:

// example map
Map<LocalDateTime, String> map = new HashMap<>();
// add some values
LocalDateTime now = LocalDateTime.now();
map.put(now, "now");
map.put(now.minusYears(1), "last year");
map.put(now.plusYears(1), "next year");
// get the entry Set from the map, each Element is of type Map.Entry<LocalDateTime, String>
// and this is the type the Set holds (what you need to put in < >)
// now you also see that programmers are totally creative and why they named the method entrySet()
Set<Map.Entry<LocalDateTime, String>> entrySet = map.entrySet();
// now you can iterate over the set, again, each element is of type Map.Entry<LocalDateTime, String>
for (Map.Entry<LocalDateTime, String> entry : entrySet) {
    System.out.format("key:%s || value:%s%n", entry.getKey(), entry.getValue());
}

Thomas

Poziom 41 , Bayreuth, Germany

15 lutego, 21:36

przydatny

Same here, there are not 10 elements inside the map. Fix that first. Then rethink your remove call... it requires an index... what did you pass it? Use the main method to test your code... testing is more important than coding. Or better, as programmer you probably will spend more time testing than coding.

public static void main(String[] args) {
    HashMap<String, Integer> map = utworzMap();
    usunPozycjeZmap(map);
    map.entrySet().forEach(System.out::println);
}