import model.Carro;
import dao.CarroDAO;

public class Teste {

    public static void main (String[] args){

    Carro carro = new Carro();

    carro.setMarca("Chevrolet");
    carro.setModelo("Cruze");
    carro.setChassi(2.4);
    carro.setRenavam(2.5);
    carro.setMotor(1.6F);

    new CarroDAO().save(carro);
 }
}

Exception in thread "main" java.lang.RuntimeException:  java.lang.ClassNotFoundException: org.postgresql.Driver
at dao.ConnectionFactory.getConnection(ConnectionFactory.java:19)
at dao.CarroDAO.<init>(CarroDAO.java:21)
at teste.Teste.main(Teste.java:18)
Caused by: java.lang.ClassNotFoundException: org.postgresql.Driver
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at dao.ConnectionFactory.getConnection(ConnectionFactory.java:16)

package DAO;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class ConnectionFactory {

private String url = "jdbc:postgresql://localhost:5432/carro";
private String username = "postgres";
private String password = "";


public Connection getConnection(){
    try{
        Class.forName("org.postgresql.Driver");
        return DriverManager.getConnection(url,username,password);
    }catch(SQLException | ClassNotFoundException e){
        throw new RuntimeException(e);
    }
 }
}