How to add user input to ArrayList?

Question

I have the following code:

public ArrayList[] username = new ArrayList[1];
public ArrayList[] password = new ArrayList[1];

public void save(String username, String password){
    String uname = userField.getText();
    String pword = passField.getText();

    username.add(uname);
    password.add(pword);
}

I am trying to make an ArrayList of usernames and passwords (using Window Builder) and add to it when someone wants to create a new user/pass. However I get an error saying "The method add(String) is undefined for the type String."

How do I fix and how do I make it so that the size of my array list can grow as new users are added?

you may be using a higher version of jdk and that is causing a problem generics may be the issue here. always specifying type of object before adding is the right approach and btw arraylist is dynamic no need to specify the size in constructor — vikeng21
– vikeng21, Commented Aug 9, 2014 at 5:12
I think you misunderstand what ArrayList actually is, take a look at Collections — MadProgrammer
– MadProgrammer, Commented Aug 9, 2014 at 7:18

Steve Kuo · Accepted Answer · 2014-08-09 05:09:02Z

2

public ArrayList[] username = new ArrayList[1];

creates an array of ArrayList. What you want is a an ArrayList of Strings.

public ArrayList<String> usernames = new ArrayList<String>();

It is good practice to "program to the interface", in this case usernames is a List, whose implementation just happens to be an ArrayList.

public List<String> usernames = new ArrayList<String>();

answered Aug 9, 2014 at 5:09

Steve Kuo

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OneMoreError · Accepted Answer · 2014-08-09 05:49:25Z

2

Why are you maintaining the usernames and passwords in two different lists ?

Your assumption is based that on matching the indexes of both the lists, and then fetching the usernames and passwords for one specific user.

You should avoid doing that. Use a more suited data structure like a map, which maintains a mapping between a key and a value.

public class UsernamePassword
{

    private Map<String, String> map = new HashMap<String, String>();

    public void save(String username, String password){
        String uname = userField.getText();
        String pword = passField.getText();

        map.put(unmae, pword);
    }
}

answered Aug 9, 2014 at 5:49

OneMoreError

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Vamsi Chilamakurthi · Accepted Answer · 2017-03-14 12:19:52Z

0

Hope you are using java version compatible with generics(1.5 or more).You should give the type parameter as String like Steve said.

You can also create a user class

public class User{
 String uname;
 String pwd;
 public User(u,p){
   uname=u;
   pwd=p; 
 }
}

and create an ArrayList of those user objects in the main class

ArrayList<User> list=new ArrayList<>();

and add those user objects with values retrieved from the fields to the list

list.add(new User(uname,pword))

answered Mar 14, 2017 at 12:19

Vamsi Chilamakurthi

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