What design pattern converts the interface of a class into another interface that clients expect?

The Adapter Pattern is a structural design pattern that allows objects with incompatible interfaces to work together by converting the interface of one class into an interface that clients expect. The primary purpose of the Adapter Pattern is to enable compatibility between different interfaces, making it easier to integrate existing systems or components without modifying their internal implementation.

In practical use, when a class is designed to work with one type of interface but needs to interact with another, an adapter can be created that implements the expected interface. This adapter acts as a bridge, translating calls from the client into the appropriate calls for the underlying class, hence enabling functionality that might otherwise be impossible due to incompatible interfaces.

This pattern is particularly valuable when integrating legacy systems with new applications, allowing developers to avoid extensive rewrites or changes to existing code. By utilizing the Adapter Pattern, you can create flexible systems that can adapt to new requirements while still leveraging existing components.