Question

In this loop, I am iterating through an ArrayList of type Entity, which contains objects of type Entity as well as objects of type Projectile, which extends Entity. I want the below code to be executed if the object is an instance of Projectile. However, the getVelocity() method is only in the subclass Projectile, and not in Entity. So I am unable to compile the below code.

I can think of ways to work around this, such as using separate ArrayLists. However, the point was to keep all Entities within a global list rather than separate them. Is there a simple solution to this problem, or do I need to change the structure of my code?

for (Entity f: glo.getList()) {
           if (f instanceof Projectile)
              f.setX(f.getVelocity()/rawFPS);
        }

Answer 1

You have to cast it as a Projectile for it to compile. Try this:

for (Entity f: glo.getList()) {
           if (f instanceof Projectile)
              f.setX(((Projectile)f).getVelocity()/rawFPS);
        }

This happens because java always checks the type that an object is declared as; In your case this is Entity.

You may want to add a @SuppressWarnings("unchecked") so that your IDE and anyone that reads your code knows that the unchecked cast is intentional.