Dzień Dobry, poproszę wytłumaczenie.

Pytania dotyczące zadania

Dyskutowane

public class Solution { public static void main(String[] args) { printIdea(new Idea()); } public static class Idea{ public String getOpis(){ return "Rolito"; } } public static void printIdea(Idea idea){ System.out.println(idea.getOpis()); } } mam kilka pytań odnośnie tego kodu. część wydaje mi się, że rozumiem. Metoda printIdea, która w nawiasie ma nazwę klasy oraz idea z małej literki które jest traktowane jako argument 'this' i przez to można się odnieść do Stringa, który nie jest statyczny? Gdy zmieniam literę na Idea.getOpis() to pokazuje błąd, że nie można się odwołać do metody niestatycznej. I jeszcze pytanko odnośnie metody main. Rozumiem, że jest wywoływana metoda printIdea ale o co chodzi że słówkiem 'new'? Dziękuję za pomoc z góry :3

1. W klasie Solution utwórz publiczną, statyczną klasę Idea
2. W klasie Idea zadeklaruj metodę public String getOpis(), która zwraca niepusty ciąg
3. W klasie Solution utwórz statyczną, publiczną metodę void printIdea(Idea idea), która będzie wyświetlać opis idei (to, co zwraca metoda getOpis)

Wymagania:

W klasie Solution utwórz publiczną, statyczną klasę Idea.
W klasie Idea utwórz publiczną metodę getOpis() typu String.
Metoda getOpis musi zwracać jakiś niepusty ciąg.
W klasie Solution utwórz publiczną, statyczną metodę void printIdea(Idea idea).
Metoda printIdea powinna wyświetlać opis idei na ekranie.

package pl.codegym.task.task06.task0617; /* Notes na nowe idee */ public class Solution { public static void main(String[] args) { printIdea(new Idea()); } public static class Idea{ public String getOpis(){ return "Rolito"; } } public static void printIdea(Idea idea){ System.out.println(idea.getOpis()); } //tutaj wpisz swój kod }

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Guadalupe Gagnon

Poziom 37 , Tampa, United States

21 grudnia 2023, 17:30

przydatny

The static modifier marks items (inside of classes) as object independent. This means that you do not need to create an object of the class that the static item resides in to use that static item. You may not have realized it, but you have been using static methods and non-static methods since the beginning of this course. Think of how you write code to take in user input; you either use a BufferedReader ,or Scanner, with the readLine(), or nextLine(), methods. These methods are not static so you must create/initialize the object first before using the method. As example:

BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
String test = input.readLine(); // "input" is initialized object to use the rdln() method

Now, if you have had a task where the user is to enter numbers you probably used Integer.parseInt() method to convert the String that was read from the keyboard to an int. The parseInt() method is static and does not require an object to call it, you only need to type the class name that it resides in (the Integer class) and the method:

BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
String test = input.readLine(); // "input" is initialized object to use the rdln() method
// prsInt() is static so doesn't need an object. Just call it using its full name, which is where it resides
int num = Integer.parseInt(test);

The Integer class is part of Java's standard library, but if you used a static method/class/variable that was in another package you either need to include a "using" statement or include the pathway to the package as part of the name. You will learn more about this as you learn the Java language.

Guadalupe Gagnon

Poziom 37 , Tampa, United States

21 grudnia 2023, 18:13

Now with methods: When you declare a method you MUST include 3 things: 1) a return value 2) a name 3) parameters, which are enclosed in parentheses The access modifier is sort of required as well, however if you do not add it then Java will automatically use a default package access modifier. The static modifier is optional as well as a few more that I won't get into to keep things simple. So in this task their is the method:

public static void printIdea(Idea idea){
    System.out.println(idea.getOpis());
}

The three "must" haves of the printIdea() method are: 1) a return value specified as "void" (which means it does not return anything) 2) the name of "printIdea" 3) parameters of an "Idea" object which it simply names "idea" It also has an access modifier of "public" specified and the optional "static" modifier. After a method has been declared you can call it in any method (including itself, which is called recursion). You do this by using the method's name and passing arguments inside parentheses that match the method's parameters. Line 9 uses the printIdea() method and passes an object, which it creates on the same line, to that method that matches the parameter of an Idea the method expects. That Idea created on line 9 gets passed to the method and used inside the method. Inside the method it simply uses the object passed in to call the method getOpis(). This method is not static, returns a String, and has no parameters. Because it is not static it needs an object to be called in the first place. Notice how line 9 has the printIdea() method called without an object but line 17 uses the variable "idea" to call the getOpis() method.