When and in what cases have you created or modified interfaces in your projects?

Interfaces in Java are created or modified when there is a need to define a contract for classes without implementation, providing flexibility and extensibility.

Examples of cases:

• When it is necessary to specify a set of methods that different classes must implement, for example, the Comparable interface for comparing objects.
• When designing architecture using SOLID principles, especially Dependency Inversion.
• To add new capabilities without changing existing classes — a new interface can be added and implemented in the necessary classes.

For example, I created a PaymentProcessor interface with a processPayment() method, so that different payment methods (credit card, PayPal) implement this interface in their own way, which facilitates extending functionality without changing client code.