Adapter Pattern

The Adapter pattern exists for one narrow, useful reason: the client contract is acceptable, but the dependency contract is not.

That is a common Java problem. A library callback, legacy service, vendor SDK, or framework type exposes methods that do not match what your application wants to depend on. Adapter lets you isolate that mismatch instead of leaking it across the codebase.

In Java, object adapters are usually the default because they work cleanly with composition and do not fight single inheritance. Class adapters still exist, but they are a niche choice.

This section focuses on four practical questions:

• how to implement adapters without turning them into mini-services
• when composition beats inheritance
• how listener and callback adapters differ from dependency wrappers
• which use cases genuinely deserve an adapter layer

Adapter is strong when it protects the application from an awkward dependency. It is weak when it is just a thin alias for methods the rest of the system already understands.

In this section

• Implementing Adapter Pattern in Java
  Implement Java adapters by keeping the target interface narrow, preferring object adapters, and isolating translation logic at the dependency boundary.
• Class Adapter vs. Object Adapter
  Compare class and object adapters in Java, with emphasis on why composition-based object adapters are usually the safer default.
• Interface vs. Implementation Adapters
  Distinguish listener and callback adapters from dependency wrappers so Java adapter code stays purposeful instead of generic.
• Adapter Pattern Use Cases and Examples in Java
  See where the Adapter pattern genuinely helps in Java systems, from legacy APIs and vendor SDKs to testing seams and incremental migrations.