Although the result is the correct one, the code does not validate. Any ideas, why this is so?

Question about the task

Playing Javarella

Java Syntax, Level 7, Lesson 9

Resolved

Thanks for your replies!

1. Enter 20 numbers from the keyboard, save them in a list, and then sort them to three other lists:
Numbers divisible by 3 (x%3==0), numbers divisible by 2 (x%2==0), and all other numbers.
Numbers simultaneously divisible by 3 and 2 (for example 6) go into both lists.
The order in which the lists are declared is very important.
2. The printList method should display each list item on a new line.
3. Using the printList method, display these three lists. First, the list for x%3, then the list for x%2, and then the last list.

Requirements:

Declare and immediately initialize 4 ArrayList<Integer> variables. The first list will be the main one. The other lists will be supplementary.
Read 20 numbers from the keyboard and add them to the main list.
Add to the first supplementary list all numbers in the main list that are divisible by 3.
Add to the second supplementary list all numbers in the main list that are divisible by 2.
Add to the third supplementary list all the remaining numbers from the main list.
The printList method should display each element of the passed list on a new line.
The program should display the three supplementary lists using the printList method.

package com.codegym.task.task07.task0713; import java.io.BufferedReader; import java.io.InputStreamReader; import java.util.ArrayList; import java.util.List; /* Playing Javarella */ public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); // Declare and initialize main list. ArrayList <Integer> list = new ArrayList<>(); // Read 20 numbers from the keyboard and add them to the main list. for (int j = 0; j < 20; j++) { String s = reader.readLine(); int x = Integer.parseInt(s); list.add(x); } // call printList method printList(list); } public static void printList(List<Integer> list) { // Declare and initialize 3 supplementary lists. ArrayList <Integer> listDiv_3 = new ArrayList<>(); ArrayList <Integer> listDiv_2 = new ArrayList<>(); ArrayList <Integer> listOthers = new ArrayList<>(); // Add numbers to the supplementary lists for (int i = 0; i < 20; i++) { if (list.get(i)%3 == 0 && list.get(i)%2 == 0) { listDiv_3.add(list.get(i)); listDiv_2.add(list.get(i)); } else if (list.get(i)%3 == 0) { listDiv_3.add(list.get(i)); } else if (list.get(i)%2 == 0) { listDiv_2.add(list.get(i)); } else { listOthers.add(list.get(i)); } } // print each list element of the supplementary lists on a new line for (int i = 0; i < listDiv_3.size(); i ++) { System.out.println(listDiv_3.get(i)); } for (int j = 0; j < listDiv_2.size(); j++ ) { System.out.println(listDiv_2.get(j)); } for (int k = 0; k < listOthers.size(); k++) { System.out.println(listOthers.get(k)); } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

15 September 2020, 14:01

solution

The problem is that the above code doesn't follow the directions. Even though the code does use the correct logic, the methods are not working as intended according to the requirements and the validation fails. Use this outline and add in the proper code. You will pass:

public static void main(String[] args) throws Exception {
   // create and initialize 3 lists according to conditions
   // read 20 numbers from the keyboard, separate them according to conditions
   // print(list1);
   // print(list2);
   // print(list3);
}

public static void printList(List<Integer> list) {
   // print the passed in list. Each value on a new line
}

Michael

Level 10 , Dresden, Germany

16 September 2020, 09:58

Hello Guadalupe, many thanks for outlining the reason why my code is not validating. You are absolutely right, I did not follow the code structure codegym wanted me to use. I should be able to create the correct code now. 👏👏👏

Michael

Level 10 , Dresden, Germany

19 September 2020, 11:13

Thanks! Challenge solved with your help!

Michael

Level 10 , Dresden, Germany

15 September 2020, 09:40

Many thanks for your hint! I looked again at the logic of line 41. Why might codegym's validator complain, if I iteratate through all the items of the main list in order to fill the supplementary lists?

dhanush

Level 30 , Chennai, India

15 September 2020, 13:15

Actually when you iterate loop the compiler starts to check the indices from 0 and then it iterate to last element 19 (which is 20) when you declare the last element as 20 means it is outofbound, so that only it doesn't verify and throws a OutOfBoundException.

for(int i=0; i<19; i++){ //this loop works fine because it iterates to before the last element
}

but don't use number to check the loop use inbuild method size() to find the size of the list and loop through the list it give the exact result

for(int i=0; i<list.size(); i++){ //this is the efficient way to find/loop through the list
}

Guadalupe Gagnon

Level 37 , Tampa, United States

15 September 2020, 14:27

i < 19 would only work for a length of 19. It would iterate to the 18 and break before index 19. The correct way for a length of 20 is i < 20, which list.size() in this case would return 20.

Michael

Level 10 , Dresden, Germany

16 September 2020, 09:07

thanks to both of you 😎

dhanush

Level 30 , Chennai, India

12 September 2020, 08:53

Let me give you a simple hint the problem is with the line 41. If you find and solve that everything is fine i think so.