When do you choose interface over an abstract class or vice versa?

When do you choose interface over an abstract class or vice versa?

If you have an implementation that will be the same for all the derived classes, then it is better to go for an abstract class instead of an interface. So, when you have an interface, you can move your implementation to any class that implements the interface. Where as, when you have an abstract class, you can share implementation for all derived classes in one central place, and avoid code duplication in derived classes.