Adapter Pattern in Java: How to Bridge Legacy Systems With Modern Code

The Adapter Pattern, also called the Wrapper, is a structural design pattern in Java that allows incompatible interfaces to work together without modifying either side. First defined by the Gang of Four in 1994, it solves a common enterprise problem where legacy components, third-party SDKs, or external services have contracts that don't match a system's core domain model. The pattern involves four key participants: the Target interface, the Client, the Adaptee, and the Adapter itself, which translates calls between the two incompatible sides. Java developers typically implement it using composition rather than inheritance, known as the Object Adapter approach. This avoids costly rewrites, prevents tight coupling in client code, and preserves already-validated business logic in existing components.