Storing objects

class User implements Serializeable {
     String UserName;
}
class Driver implements Serializeable {
     User user;

     public Driver( String name ) {
          this.user = new User();
          this.user.UserName = name;
     }
}
class Passenger implements Serializeable {
     User user;

     public Passenger( String name ) {
          this.user = new User();
          this.user.UserName = name;
     }
}
class Car implements Serializeable {
     Driver driver;
     Passenger passenger;

     public Car( Driver driver, Passenger passenger ) {
          this.driver = driver;
          this.passenger = passenger;
     }
}
class Garage implements Serializeable {
     Car[] cars;
     private int i = 0;

     public Garage() {
          this.cars = new Car[ 3 ];
     }

     public void Add( Car car ) {
          if( this.i != 3 ) {
               this.cars[ this.i++ ];
          }
          else {
               throw new Exception();
          }
     }
}

Garage garage = new Garage();
Car car;

car = new Car( new Driver( "acey" ), new Passenger( "Rudolph" ) );
garage.Add( car );

car = new Car( new Driver( "Rudolph" ), new Passenger( "acey" ) );
garage.Add( car );