cannot infer type arguments for ArrayList<>

Question

I'm trying to make an ArrayList that contains an object of another class, a name, and turn. something similar to the python's dictionary.

self.user1 = {"user":user1,"name":empty,"turn":empty}

so I made a class that has the 3 values.

class User{
public userInterface user1;
String name;
String turn;

public User(UserInterface user1,String name,String turn) {
    this.user1=user1;
    this.name=name;
    this.turn=turn;
}}

and I'm trying to call it in the constructor of main class as following:

public class MainClassConstructon{
ArrayList<User> user1;
ArrayList<User> user2;

MainClassConstructon(UserInterface user1 ,UserInterface user2){
     this.user1 = new ArrayList<>(new User(user1,empty, empty));
     this.user2 = new ArrayList<>(new User(user2,empty, empty));

but it raises an error saying that: cannot infer type arguments for ArrayList<>.

Answer 1

ArrayList has three constructors:

public ArrayList(int initialCapacity)
public ArrayList()
public ArrayList(Collection<? extends E> c)

User is neither an int nor a Collection , and you're passing an argument so the middle constructor doesn't apply either.

But that's beside the point, your goal is to create a single list of users, so instead of doing what you're currently doing, you need to use only a single list, and simply add your users:

public class MainClassConstructon{
  List<User> users; // Or ArrayList, doesn't really matter

  MainClassConstructon(UserInterface user1 ,UserInterface user2){
    users = new ArrayList<>(); // Diamond syntax, requires Java 7+
    users.add(new User(user1, "", ""));
    users.add(new User(user2, "", ""));
  }
}

Answer 2

you can try it like this

public class MainClassConstructon {
    ArrayList<User> user1 = new ArrayList<>();
    ArrayList<User> user2 = new ArrayList<>();

    MainClassConstructon(UserInterface user1, UserInterface user2) {
        this.user1.add(new User(user1, "", ""));
        this.user2.add(new User(user2, "", ""));
    }
}

Answer 3

I'm not a java developer but i suggest you try and look on Arraylist api.

Here is what i found online, sry if it doesn't help :)

import java.util.*; 
public class ArrayListDemo { public static void main(String args[]) { 
// create an array list 
ArrayList al = new ArrayList(); 
System.out.println("Initial size of al: " + al.size()); 
// add elements to the array list 
al.add("C"); 
al.add("A"); 
al.add("E"); 
al.add("B"); 
al.add("D"); 
al.add("F"); 
al.add(1, "A2"); 
System.out.println("Size of al after additions: " + al.size());

 // display the array list System.out.println("Contents of al: " + al);

 // Remove elements from the array list al.remove("F");
al.remove(2); 
System.out.println("Size of al after deletions: " + al.size());
 System.out.println("Contents of al: " + al); 
}
}

Answer 4

well i made it like this:

this.user1 = new ArrayList<>(Arrays.asList(new User(user1,empty, empty)));

and was able to access it by:

t.user1.get(0).name="bla bla";