I'm new to Java and trying to make a simple program which holds track of the fuel usage. I thought this would be a good exercise.

```
public class MyJavaProgram {

    static Car myCar = new Car("Audi");

    public static void main(String[] args) {

        System.out.println(myCar);

        myCar.refuel(100);
        myCar.drive(50);
        myCar.drive(20);

    }

}

```

Normally in Java this code would print out something like: "package.Animal@", but here is what I get in my console:

```
> A new Audi has been created.
> 
> Car refilled with 100 liter fuel. 
> Car drove 50 km. 
> Car drove 20 km.

```

My Car class:

```
public class Car {

    String type;
    int fuel = 0;
    int driven;

    public Car(String type) {
        this.type = type;
        System.out.println("A new "+type+" has been created.");
    }

    public void refuel(int amount) {
        fuel += amount;
        System.out.println("Car refilled with "+amount+ " liter fuel.");
    }

    public void drive(int amount) {
        fuel -= amount;
        driven += amount;
        System.out.println("Car drove "+amount+" km.");
    }

    public String toString() {
        return "";
    }

}

```

I can not see what part of my code causes this bug.