public interface Quackable extends QuackObservable {
    void quack();
    void registerObserver(Observer observer);
    void notifyObservers();
}

• Explanation:

1. public interface Quackable extends QuackObservable {
   • This declares a public interface named Quackable.
   • It extends the QuackObservable interface, indicating that objects implementing Quackable can be observed for quacking events.
2. void quack();
   • This declares an abstract method quack.
   • Classes implementing the Quackable interface will provide concrete implementations for making a quacking sound.
3. void registerObserver(Observer observer);
   • This declares an abstract method registerObserver, taking an Observer parameter.
   • Classes implementing the Quackable interface will provide concrete implementations for registering observers interested in their quacking events.
4. void notifyObservers();
   • This declares an abstract method notifyObservers.
   • Classes implementing the Quackable interface will provide concrete implementations for notifying registered observers when they quack.
5. }
   • Closes the Quackable interface.

• Overall Explanation:
  • The Quackable interface is designed to be implemented by classes representing objects that can quack.
  • It extends the QuackObservable interface, indicating that quackable objects can also be observed for quacking events.
  • Classes implementing Quackable will provide specific implementations for making a quacking sound (quack method) and managing observers (registerObserver and notifyObservers methods).
  • The interface enforces a common set of methods for quacking objects, allowing them to be treated uniformly in the code, regardless of their specific implementation details.

This interface is a key component in the implementation of the Observer Pattern for observing quacking behavior in various duck classes.