Java – when an object is an instance of a base class, call the correct method for the object

I have the following examples in Java:

public abstract class Vehicle {
    private final String name;
    private final String make;

    public Vehicle(final String name,final String make) {
        this.make = make;
        this.name = name;
    }
}

public final class Car extends Vehicle {
    public Car(final String name,final String make) {
        super(name,make);
    }
}

public final class Truck extends Vehicle  {
    final Integer grossVehicleWeight;

    public Truck(final String name,final String make,final Integer gvw) {
        super(name,make);
        this.grossVehicleWeight = gvw;
}

I want to use the car to do some work, and the work does not depend on the subclass of the vehicle Therefore, I have a method in another class, as follows:

public void doStuff(public final Vehicle vehicle) {
    //do stuff here
    //then insert it into my database:
    insertVehicle(vehicle);
}

However, I want to do different things in insertvehicle, so I override this method for each subclass:

public void insertVehicle(Car car) { //do stuff for a car }

public void insertVehicle(Truck truck) { //do stuff for a truck }

In my dostuff method, I can use instanceof to determine the vehicle category (car or truck), then project the vehicle to this class and call the insertvehicle method, as shown below:

public void doStuff(public final Vehicle vehicle) {
    //do stuff here
    //then insert it into my database:
    if (vehicle instanceof Car) {
        insertVehicle((Car) vehicle);
    } else {
        insertVehicle((truck) vehicle);
    }
}

However, I have read that using instanceof is not the best way one

How can I best redo this so that I don't have to use instanceof?

Solution

You can use visitor mode:

public interface VehicleVisitor {
    public void visit(Car car);
    public void visit(Truck truck);
}

public class Car extends Vehicle {

    @Override
    public void insert(VehicleVisitor vehicleVisitor) {
        vehicleVisitor.visit(this);
    }
}

public class Truck extends Vehicle {
    @Override
    public void insert(VehicleVisitor vehicleVisitor) {
        vehicleVisitor.visit(this);
    }
}

public abstract class Vehicle {
    public abstract void insert(VehicleVisitor vehicleVisitor);
}

public class VehicleVisitorImpl implements VehicleVisitor {

    @Override
    public void visit(Car car) {
        System.out.println("insert car");
    }

    @Override
    public void visit(Truck truck) {
        System.out.println("insert truck");
    }
}

public class Main {

    public static void main(String[] args) {
        Vehicle vehicle = new Car();
        // finally the agnostic call
        vehicle.insert(new VehicleVisitorImpl());
    }

}