Super simple problem with ArrayList in Java
public class Cliente {
    private static String user;
    private static String password;
    public Cliente (String usr, String pass) {
        user = usr;
        password = pass;
    }
    public String getUser() {
        return user;
    }
}

public class AddToArrayList{
    static ArrayList<Cliente> listaClientes = new ArrayList<Cliente>();

    public static void main(String[] args) throws IOException {

        Cliente c1 = new Cliente("pepe","pepe1");
        Cliente c2 = new Cliente("jose","jose1");
        Cliente c3 = new Cliente("edu","edu1");
        listaClientes.add(c1);
        listaClientes.add(c2);
        listaClientes.add(c3);

        printArraList();
    }

    public static void printArraList() throws IOException {
        for (Cliente c : listaClientes) {
            System.out.println(c.getUser());
        }
    }

private static String user;
private static String password;

private String user;
private String password;