Can't Get Hibernate (Java) Working

I must be doing this all wrong, but I don't know quite how to make it do exactly what I want. I have three files:

RunMe.java - something to test my code with

package hib;

public class RunMe {

	public static void main(String[] args) {
		DbCommunicator db = new DbCommunicator();
		
		//db.register("John", "Smith", "me", "qwerty", "[email protected]");
		System.out.println(db.checkCredentials("user", "pass"));
		System.out.println(db.getFirst());
		System.out.println(db.getLast());
	}

}

UserDatabase.java - represents my database

package hib;

public class UserDatabase {
	
	private int id;
	private String username;
	private String password;
	private String first;
	private String last;
	private String email;
	private long attributes;
	
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	public String getFirst() {
		return first;
	}
	public void setFirst(String first) {
		this.first = first;
	}
	public String getLast() {
		return last;
	}
	public void setLast(String last) {
		this.last = last;
	}
	public String getEmail() {
		return email;
	}
	public void setEmail(String email) {
		this.email = email;
	}
	public long getAttributes() {
		return attributes;
	}
	public void setAttributes(long attributes) {
		this.attributes = attributes;
	}
	
}

DbCommunicator.java - used to do transactions

package hib;

import java.util.*;
import org.hibernate.*;
import org.hibernate.cfg.*;

public class DbCommunicator {
	
	public int register(String first, String last, String username, String password, String email)
	{
		Session session = null;
		try {
			SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
			session = sessionFactory.openSession();
			
			// Find the next available ID number
			int I = 0;
			while(true)
			{
				List<?> list = session.createQuery("select db.id from UserDatabase db where db.id='" + I + "'").list();
				Iterator<?> iter = list.iterator();
				
				if(!iter.hasNext())
				{
					//int id = (Integer)iter.next();
					System.out.println(I);
					break;
				}
				
				I++;
			}
			
			// Check to see if the username is available
			List<?> list = session.createQuery("select db.username from UserDatabase db where db.username='" + username + "'").list();
			Iterator<?> iter = list.iterator();
			
			if(!iter.hasNext())
			{
				session.flush();
				session.close();
				return 2;		// Username already exists
			}
			
			Transaction tx = session.beginTransaction();
			UserDatabase db = new UserDatabase();
			
			db.setId(I);
			db.setFirst(first);
			db.setLast(last);
			db.setUsername(username);
			db.setPassword(password);
			db.setEmail(email);
			db.setAttributes(0);
			session.save(db);
			
			tx.commit();
		}
		catch(Exception e) {
			e.printStackTrace();
			
			session.flush();
			session.close();
			return 1;		// Exception thrown
		}
		
		session.flush();
		session.close();
		return 0;		// No errors!
	}
	
	public int checkCredentials(String username, String password)
	{
		Session session = null;
		
		try {
			SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
			session = sessionFactory.openSession();
			
			List<?> list = session.createQuery("from UserDatabase").list();
			Iterator<?> iter = list.iterator();
			UserDatabase db = null;
			
			while(iter.hasNext())
			{
				db = (UserDatabase)iter.next();
				if(username.equals(db.getUsername()))
				{
					if(password.equals(db.getPassword()))
					{
						session.flush();
						session.close();
						return 0;
					}
					else
					{
						// Password mismatch!
						session.flush();
						session.close();
						return 1;
					}
				}
			}
		}
		catch(Exception e) {
			e.printStackTrace();
		}
		
		// Could not connect to database, or username is wrong
		session.flush();
		session.close();
		return 2;
	}
	
	public int getId() {
		UserDatabase db = new UserDatabase();
		return db.getId();
	}
	public String getUsername() {
		UserDatabase db = new UserDatabase();
		return db.getUsername();
	}
	public String getPassword() {
		UserDatabase db = new UserDatabase();
		return db.getPassword();
	}
	public String getFirst() {
		UserDatabase db = new UserDatabase();
		return db.getFirst();
	}
	public String getLast() {
		UserDatabase db = new UserDatabase();
		return db.getLast();
	}
	public String getEmail() {
		UserDatabase db = new UserDatabase();
		return db.getEmail();
	}
	public long getAttributes() {
		UserDatabase db = new UserDatabase();
		return db.getAttributes();
	}

}

output

0
null
null

The checkCredentials() code works just fine. But I want to be able to retrieve the data from the database afterwards. I thought the UserDatabase was populated with values. Evidently, it's not working the way I expected it to. Can anyone help me understand where I'm going wrong and what I can do with my code to make it work?

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