error on BufferedReader

Question sur la mission

Discussion en cours

Hi guys, could anyone tell me why it tells me something is wrong with my BufferedReader? I have been using this often and it hasn't said anything until now so I guess it might be something else? Also I return the media already but it says I have to add a return type. I don't really understand.

Utilise le clavier pour saisir des nombres, puis calcule la moyenne arithmétique.
Si l'utilisateur saisit -1, affiche la moyenne arithmétique de tous les nombres saisis et termine le programme.
-1 ne doit pas être inclus dans le calcul.

Voici quelques exemples :
a) Si tu saisis les nombres
1
2
2
4
5
-1
nous affichons
2.8

b) Si tu saisis les nombres
4
3
2
1
-1
nous affichons
2.5

Indice : une des solutions à ce problème utilise la construction suivante :

while (true) {
    int nombre = lire le nombre;
    if (vérifie si le nombre est -1)
        break;
}

Impératifs :

Le programme doit lire les données depuis le clavier.
Le programme doit afficher des données à l'écran.
Après avoir saisi -1, le programme doit se terminer correctement.
Si tu saisis les nombres 1, 2, 2, 4, 5 et -1, le programme doit afficher 2.8.
Si tu saisis les nombres -100, 0, 100 et -1, le programme doit afficher 0.0.
Si tu saisis les nombres 1 et -1, le programme doit afficher 1.0.
Le résultat affiché doit correspondre aux conditions de tâche pour toute donnée d'entrée.

package fr.codegym.task.task05.task0507; /* Moyenne arithmétique */ public class Solution { public static void main(String[] args) throws Exception { calculateMedia(); } public static calculateMedia() { BufferedReader r = new BufferedReader(new InputStreamReader(System.in)); int i; while (true) { if (nb-1) { float media = (float) sum / i; return media; break; } int nb = r.readLine(); i++; int sum = sum+nb; } } }

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Niriya

niveau France, France, France

12 décembre 2023, 08:41

Thank you for the detailed answer, I make lots of small mistakes. I am fixing them. Though the error message I got was about the BufferedReader not being found and it didn't seem to be about the other errors I made. I didn't know what I did wrong on this one so I couldn't debug the rest of the code. fr/codegym/task/task05/task0507/Solution.java:13: error: cannot find symbol BufferedReader r = new BufferedReader(new InputStreamReader(System.in)); ^

Guadalupe Gagnon

niveau Tampa, Tampa, United States

12 décembre 2023, 14:21

you need to import the classes that you use. I forget about this because IntelliJ automatically just adds the import statements in when I am typing code without me having to find the correct import statements. In your case you are using the BufferedReader and InputStreamReader classes of the java.io package. So you need import statements for each:

import java.io.BufferedReader;
import java.io.InputStreamReader;

When you use a bunch of classes in the same package you can simplify the import statement to specify that you want all the classes in that package like this:

import java.io.*;

If you get an error like this again make sure that you have the proper import statement. You can always refer to the Java docs for help, or simply type what import statement to use into google.

Guadalupe Gagnon

niveau Tampa, Tampa, United States

12 décembre 2023, 14:35

Being able to algorithmically solve problems is one of the harder things for people to learn when it comes to computer programming. You may have a lot of little mistakes with the rules of Java, but I can see what your code intends to do and the algorithmic logic is correct. ALL new programmers make these little mistakes as they are learning the intricacies of the language, so expect that.

Guadalupe Gagnon

niveau Tampa, Tampa, United States

11 décembre 2023, 15:36

#1 Line 12: In Java method declarations require that a return type is specified. In the code above the main() method is correct because it has void (meaning no return) specified as the return type. The calculateMedia() method is not correct because it is missing the return type. In the method body I see that you are returning 'media', which is a float, so the method declaration should have float as the the return type. #2 Line 14 and line 22: Line 14 declares the int i and line 22 increases 'i' by 1 each cycle. The problem is that 'i' is never initialized. It looks like 'i' is being used to count each loop cycle so it should be initialized to 0. #3 Line 16 and 21: Line 16 uses the variable "nb', however that does variable is not declared until line 21. This means at line 16 it does not exist and can not be used. You will need to fix this so that the variable is declared before it is used. #4 Line 17 and 22: This has same problem as #3 for the variable sum. #5 Line 17: When you divide two integers by each other the result will be an integer. Because integers can only be whole numbers, this means any fraction remaining that would be expressed as a decimal value is removed (not rounded, just removed). Take for example if you divided 3 by 2, the correct answer would be 1.5 however if you did that in Java it would be just simply 1. On line 17 you specify that it should be a float, however this conversion from int to float happens after the equation. The result of (float) 3 / 2 would still be 1, however if you output that it would output as a float and be 1.0:

System.out.println(3 / 2); // outputs 1
System.out.println((float) 3 / 2); // outputs 1.0

Guadalupe Gagnon

niveau Tampa, Tampa, United States

11 décembre 2023, 15:50

#6 Line 19 is unreachable as the return statement above ends the block of code. #7 Line 21: the readline() method of the BufferedReader class returns a String. The variable is of type int which means that this line is illegal as a String and int are incompatible types. You are going to need to make sure you convert the String to an int. #8 Line 22: the variable sum can not be initialized to sum + nb because the sum on the right side of the equals sign hasn't been initialized and has no value. #9 Line 21 and line 22 are both declared inside the while loop. A loop is a block of code that repeats indefinitely until a condition the programmer sets is met, or if no condition is set then it would be run infinitely. Because they are declared inside the loop the variables only exist each individual loop cycle, going away at the end of the cycle. Most of these are compile time errors and will need to be fixed before your code will compile and run. All of them will need to be fixed before your code will pass this task.