[FIXED] Why second parameter of objects in array list are overwritten by adding new object to array list?

Issue

I would like to get data from a CSV file. First entry is name of user, others are values. Everything works, but when I create new User object (name and bills parameters) and add it to ArrayList of Users, bills parameter of all my previous objects stored in array list are overwritten.

Main.java:

import java.io.*;
import java.util.Scanner;
import java.util.ArrayList;
import java.util.Collections;

public class Main {
  private static Scanner scanner = new Scanner(System.in);
  private static ArrayList<Integer> bills = new ArrayList<Integer>();
  private static ArrayList<User> users = new ArrayList<User>();

  public static void main(String[] args) throws Exception {
    //ArrayList<Integer> bills = new ArrayList<Integer>();
    // System.out.println("Enter full path to csv file: ");
    // String path = scanner.nextLine();
    // System.out.println("Enter delimiter: ");
    // String delimiter = scanner.nextLine();
    scanner = new Scanner(new File("..."));
    //scanner.useDelimiter(";");
    // while(scanner.hasNext()) {
    //   System.out.print(scanner.next());
    // }

    int i = 0;
    int bill;

    while(scanner.hasNextLine()) {
      i++;
      bills.clear();
      String line = scanner.nextLine();
      String[] fields = line.split(";");
      String name = fields[0];
      for (String field: fields) {
        try {
          bill = Integer.parseInt(field);
          bills.add(bill);
        } catch (NumberFormatException e) {

        }
      }
      System.out.print(name);
      System.out.println(bills);
      User newUser = User.createUser(name, bills);
      //User newUser = new User(name, bills);
      System.out.println(newUser.getName() + ">" + newUser.getBills());
      users.add(newUser);
      //System.out.println();
    }
    scanner.close();
  }

  public static void getMax(String userName) {
    for(int i = 0; i < users.size(); i++) {
      //if(users.get(i).getName().equals(userName)) {
        System.out.print(users.get(i).getName());
        System.out.println(users.get(i).getBills());
      //}
    }
  }
}

User.java:

import java.util.ArrayList;
import java.util.Collections;

public class User {
  private String name;
  private ArrayList<Integer> bills;

  public User(String name, ArrayList<Integer> bills) {
    this.name = name;
    this.bills = bills;
  }

  public String getName() {
    return this.name;
  }

  public ArrayList<Integer> getBills() {
    return this.bills;
  }

  public static User createUser(String name, ArrayList<Integer> bills) {
    return new User(name, bills);
  }
}

Solution

You are sharing the same instance of bills in every User.

Remove the static List for bills and instantiate a new one with each iteration of the loop.

while(scanner.hasNextLine()) {
  List<Integer> bills = new ArrayList<>();
  ... reading from stream happens ...
  User user = new User(name, bills);
  users.add(user);
}

Answered By - vsfDawg
Answer Checked By - Pedro (JavaFixing Volunteer)