public class QuackCounter implements Quackable {
    Quackable duck;
    static int numberOfQuacks;

    public QuackCounter(Quackable duck) {
        this.duck = duck;
    }

    public void quack() {
        duck.quack();
        numberOfQuacks++;
    }

    public static int getQuacks() {
        return numberOfQuacks;
    }

    public void registerObserver(Observer observer) {
        duck.registerObserver(observer);
    }

    public void notifyObservers() {
        duck.notifyObservers();
    }
}

• Explanation:

1. public class QuackCounter implements Quackable {
   • This declares a public class named QuackCounter.
   • It implements the Quackable interface, indicating that instances of this class can quack.
2. Quackable duck;
   • This declares a member variable named duck of type Quackable.
   • It is used to store the quackable entity that this QuackCounter is wrapping.
3. static int numberOfQuacks;
   • This declares a static member variable named numberOfQuacks of type int.
   • It will be used to count the number of quacks across all instances of QuackCounter. Being static means it is shared among all instances of the class.
4. public QuackCounter(Quackable duck) { this.duck = duck; }
   • This is the constructor of the QuackCounter class.
   • It takes a Quackable object as a parameter and initializes the duck variable with it.
5. public void quack() { duck.quack(); numberOfQuacks++; }
   • This method is part of the Quackable interface implementation.
   • It calls the quack method on the wrapped duck object, effectively delegating the quacking behavior. After quacking, it increments the numberOfQuacks.
6. public static int getQuacks() { return numberOfQuacks; }
   • This is a static method that allows access to the numberOfQuacks variable.
   • It returns the total number of quacks across all instances of QuackCounter.
7. public void registerObserver(Observer observer) { duck.registerObserver(observer); }
   • This method is part of the Quackable interface implementation.
   • It delegates the responsibility of registering observers to the wrapped duck object.
8. public void notifyObservers() { duck.notifyObservers(); }
   • This method is part of the Quackable interface implementation.
   • It delegates the responsibility of notifying observers to the wrapped duck object.
9. }
   • Closes the QuackCounter class.

• Overall Explanation:
  • The QuackCounter class is a decorator that wraps around a Quackable object to count the number of quacks.
  • It implements the Quackable interface, providing methods for quacking, registering observers, and notifying observers.
  • The quack method delegates the quacking behavior to the wrapped duck and increments the numberOfQuacks.
  • The getQuacks method allows retrieving the total number of quacks across all instances of QuackCounter.
  • This class is part of the larger design that allows counting the quacks of different types of ducks and quackable entities.