How to create an arraylist class that can store multiple objects?

Question

I am making a GUI project in which I need a matrice-type database.

How can I create a class that can store multiple objects in an ArrayList?

Answer 1

I think a better way to do this is to create a user info class to store the information of a particular user like this.

// I made them all public but this might not be a good idea!
class UserInfo {
    String user;
    String pass;
    String secretCode;
}

And you put it into an ArrayList.

ArrayList <UserInfo> InfoList = new ArrayList<UserInfo> ();    

Then for your current methods, you can do

// Not so sure what you want to do in this method... so you get to figure out that yourself!
public void userInternalDatabase (UserInfo info) {

    this.user = info.user;
    this.pass = info.pass;
    this.secretCode = info.secretCode;
}

public void addUser(String i, String j, String k) {
    UserInfo newUser = new UserInfo();
    newUser.user = i;
    newUser.pass = j;
    newUser.secretCode = k;
    InfoList.add(newUser);
}

public Object findUsername(String a)  
{    
    for (int i=0; i <InfoList.size(); i++) {
        if (InfoList.get(i).user.equals(a)){
             return "This user already exists in our database.";
        }
    }
    return "User is not founded."; // no Customer found with this ID; maybe throw an exception
}