why list1, list2, list3 like not exist in printList method?

Question about the task

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all working fine if i coment 53 , 54 , 55 lines and similar little bit down lines. thos is problem they are not allowed. how to make them exist. but why just list with all 20 lines exist?

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)); ArrayList<Integer> list = new ArrayList<Integer>(); ArrayList<Integer> list1 = new ArrayList<Integer>(); ArrayList<Integer> list2 = new ArrayList<Integer>(); ArrayList<Integer> list3 = new ArrayList<Integer>(); for (int i = 0; i < 20; i++) { list.add( Integer.parseInt(reader.readLine())); } /* for (int i = 0; i< 20; i++) { list.get(i); } */ for (int i = 0; i< 20; i++) { if ( list.get(i) % 3 == 0 ) list1.add(list.get(i)); if ( list.get(i) % 2 == 0 ) list2.add(list.get(i)); if ( !( list.get(i) % 3 == 0 ) && !( list.get(i) % 2 == 0)) list3.add(list.get(i)); } //write your code here } public static void printList(List<Integer> list) { // this.list1 = list1; for (int i = 0; i < list.size(); i++) { System.out.println(list.get(i)); /* if (i < list1.size()) System.out.println(list1.get(i)); if (i < list2.size()) System.out.println(list2.get(i)); if (i < list3.size()) System.out.println(list3.get(i)); */ } // list1, list2, list3 not reading here some mistake. /* for (int i = 0; i < list1.size(); i++) { System.out.println(list1.get(i)); } for (int i = 0; i < list2.size(); i++) { System.out.println(list2.get(i)); } for (int i = 0; i < list3.size(); i++) { System.out.println(list3.get(i)); } */ } }

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Lisa

Level 41

17 November 2021, 12:46

The printList method has a parameter list. That parameter is treated inside the method like a local variable. So when you try to access list, then you are referring to this very parameter (and not to the list reference variable in main). list1 or list2 are not known in printList and hence you can not access them. To test this, you usually pass an argument to that method. Eg. in main in line 32 add the following:

printList(list);
list1.add(1111);
printList(list1);

the first line passes the list reference to the printList method. Inside the method list is referred to as list now we add content to list1 and pass list1 to printList now list1 is addressed as list inside printList and the previously added number 1111 gets printed.

Onar D.

Level 7

18 November 2021, 15:07

thanks. it was very helpfull. just add 3 more lines of lists 1, 2 ,3.

Lisa

Level 41

18 November 2021, 16:34

great ;)