repository with generics

gistfile1.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map.Entry;

public class HelloWorld
{
  public static void main(String[] args)
  {
    
    UsersRepositoryInterface usersRepository = new UsersRepository();
    
    usersRepository.store(new User("[email protected]", "uid"));
    
    User found;
    
    found = usersRepository.findByEmail("[email protected]");
    
    System.out.println(found.getEmail());
    
    // Movie cannot be converted to User
    // usersRepository.store(new Movie());
    
  }
}

interface HasId {
  public String getId(); 
}

class User implements HasId {
  private String email;
  private String id;
  
  public User(String email, String id) {
      this.email = email; 
    this.id = id;
  }
  
  public String getEmail() {
    return email;
  }
  
  public String getId()
  {
    return id;
  }
}

class Movie implements HasId {
  public String getId() {
    return "asd";
  }
}

interface Repository<Entity extends HasId> {
 
  public void store(Entity e);
  
  public Entity find(String id) throws Exception;  
  
}

interface UsersRepositoryInterface extends Repository<User> {
  
  public User findByEmail(String email);
    
}


abstract class BaseRepository<Entity extends HasId> implements Repository<Entity>
{ 
  protected HashMap<String, Entity> storage = new HashMap<>();
  
  public void store(Entity e) {
    storage.put(e.getId(), e);
  }
  
  public Entity find(String id) throws Exception {
    return storage.get(id);
  }
  
}

class UsersRepository extends BaseRepository<User> implements UsersRepositoryInterface {
 
  public User findByEmail(String email) {
    
    for (Entry<String, User> entry : storage.entrySet()) {
    
        User user = entry.getValue();
        
        if (user.getEmail().equals(email)) {
      		return user;
    	}
    }
       
    return null;
    
  }
  
}