Components are the main building blocks in Polylith.

A component is an encapsulated block of code that can be assembled together with a base and a set of other components into services, libraries or tools. Components achieve encapsulation and composability by separating their private implementation from their public interface:

The dark green represents the implementation and the light green represents the interface.

Each component lives in a separate directory under the components directory, and contains a src, test and resources directory:

▾ workspace
▾ components
▾ mycomponent
▸ src
▸ test
▸ resources

The src directory contains at least two namespaces, one for the interface and one for the implementation:

▾ src

A component's interface is a namespace that exposes a collection of functions for other components or bases to call. Each function in a component’s interface “passes-through” to an equivalent function in its private implementation (the core namespace in this example). This “pass-through” approach enables full code navigation and refactoring, whilst maintaining encapsulation.

Code examples of components can be found in the RealWorld example app and in the Polylith Tool.