Passing in a sub-class to a method but having the super class as the parameter?

Question

I have an abstract class Vehicle with 2 implemented subclasses RedVehicle and YellowVehicle.

In another class I have a List

Answer 1

Why don't you use the visitor pattern?

That way you

• don't need type tokens
• let dynamic dispatch handle the case distinction (instead of if(v.getClass().equals(type)))
• are more flexible (following OCP)

---

In detail:

your abstract class Vehicle gets a method accept(Visitor v), with the subclasses implementing it by calling the appropriate method on v.

public interface Visitor {
  visitRedVehicle(RedVehicle red);
  visitYellowVehicle(YellowVehicle yellow);
}

Using a visitor:

public class Example {

  public void useYellowOnly() {
    exampleMethod(new Visitor() {
        visitRedVehicle(RedVehicle red) {};
        visitYellowVehicle(YellowVehicle yellow) {
             //...action
        });
  }
  public void exampleMethod(Visitor visitor){
      for(Vehicle v : vehicles) {
          v.accept(visitor);
      }  
  }
}