creating multiple objects in java oop

Question

i cant just get my head around this. i've got a user class:

public class user {

private String name;
private int age;

public user()
{
}

public String getName()
{
    return name;
}



public int getAge()
{
    return age;
}

public void setName(String kname)
{
    name = kname;
}


public void setAge(int kage)
{
    alter = kage;
}

}

and i'm creating and listing users within my userUI class

public class PersonalUI {

public static void main (String args[]) {
    int menu = 0;
    int i = 0;
    while (menu != 3)
    {   
    System.out.println("Please choose: \n (1) Create User \n (2) List User                \n              (3) Quit");
    menu = Console.readInt();
    if (menu = 1)
    {   
    User user[i] = new User();
    System.out.println("Please enter a name");
    String kname = Console.readString();
    user[i].setName(kname);
    }
}

My Problem: How can I create multiple objects as i'm getting an error for User user[i] = new User(); guess im just doing it wrong

Boris Strandjev · Accepted Answer · 2013-02-20 10:25:54Z

9

Array is not the way to go in your case. Use List:

List<User> users = new ArrayList<User>;

if (menu == 1)
{   
    User newUser = new User();
    users.add(newUser);
    newUser.setName(kname);
}

You don't know the number of users that will be entered up front - thus use dynamic data structure.

Your problem is that you are trying to do two things in the same go : create an array and assign value to specific element of it.

This is how you should operate an array:

int length = 5; // predetermined by you constant
User []users = new User[length];
//....
users[i] = new User();

Exactly because of the predetermined constant I advise using List.

edited Feb 20, 2013 at 10:25

answered Feb 17, 2013 at 13:02

Boris Strandjev

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Comments

nageswara rao · Accepted Answer · 2013-02-17 13:33:45Z

3

You can check this mistake.

User user[i] = new User();

user[i] = new User();   // add this in your code

System.out.println("Please enter a name");
String kname = Console.readString();
user[i].setName(kname);

Many think that the statement, User user[i] = new User(), creates an object of User, but it creates a reference variable. Conversion of reference variable into object is required as follows:

user[i] = new User();

This you can find more in Confusion of reference variables and objects in arrays (array of array objects)

answered Feb 17, 2013 at 13:33

nageswara rao

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Comments

PermGenError · Accepted Answer · 2013-02-17 13:07:51Z

First You should read the size of the user array from command line to define the size of your array outside the loop. then inside the loop you populate the array with appropriate elements.

     System.out.println("please enter size of the user");
    int size=console.readInt();
    User[] user = new User[size]
    while (menu != 3)
    {   
    System.out.println("Please choose: \n (1) Create User \n (2) List User                \n              (3) Quit");
    menu = Console.readInt();
    if (menu == 1)//changed, you were using assigning here (menu=1)
    {   
    user[i] = new User();

however, if you want a dynamic array, use a List implementing class like ArrayList which doesn't require you to provide size while creating the array.

   List<User> usersList = new ArrayList<User>();
   //then inside the loop populate the list with its `List#add(elem)` method

Abubakkar · Accepted Answer · 2013-02-17 13:10:59Z

Your comparison to check the menu value is wrong.

It shouldn't be menu = 1 instead it should be menu == 1.

I don't know how are you going to store the users but what I suggest is make an ArrayList that will store the user objects and whenever creating a new User object add it to the list.

And while listing the users , just iterate through the array list created.

I think this is what you need:

public static void main (String args[]) {
    int menu = 0;
    int i = 0;
    List<User> list = new ArrayList<User>();
    while (menu != 3)
    {   
    System.out.println("Please choose: \n (1) Create User \n (2) List User                \n              (3) Quit");
    menu = Console.readInt();
    if (menu == 1)
    {   
    User user = new User();
    System.out.println("Please enter a name");
    String kname = Console.readString();
    user.setName(kname);
    // add this user to the list
    list.add(user);
    }
}

exexzian · Accepted Answer · 2013-12-07 20:52:14Z

1

It should be
User user[] = new User[size]; // here you creating array of User objects of size size

And then for each user:
user[i] = new User(); // and here you are initializing each user object

edited Dec 7, 2013 at 20:52

user2613258

answered Feb 17, 2013 at 13:04

exexzian

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