Module integration is an important aspect of software design and development. Building programs using well-integrated modules promotes reusability, maintainability, and extensibility of code. Effective module integration involves careful planning at the design stage as well as best practices during implementation.

At the design phase, the key is to identify the natural breaking points in your program and define clean module interfaces. Look for logical groupings of related functionality that can be encapsulated with minimal dependencies on other modules. Aim to separate modules based on areas of change – parts of the code that tend to be modified independently. Define narrow, stable interfaces between modules using abstract data types and well-defined contracts. Consider aspects like independence of modules, cohesion within modules, and minimization of inter-module coupling during the design process.

Use interfaces or abstract base classes to decouple modules from implementation details. Define modules in a hierarchical manner with utility modules at the bottom and applications at the top depending on libraries. Group classes into consistent, well-named namespaces or packages based on functionality. Document module interfaces thoroughly so they are understandable in isolation from implementation code. Perform reviews to verify module interfaces meet design principles like the Single Responsibility Principle and Open/Closed Principle.

During implementation, focus on encapsulation and information-hiding between modules. Define module boundaries formally using language features for private/public access. Hide implementation details and minimize exposure of internal data structures and non-essential functions across module boundaries. Enforce strict separation by not allowing direct calls or accesses across module borders. Leverage dependency inversion and polymorphism to reduce tight coupling.

Use configuration over convention and dependency injection patterns for flexible composition. Define modules as plugins that can be loaded/unloaded dynamically. Avoid global resources, singletons, and tightly coupled static functions that tie modules together rigidly. Isolate module lifecycles and dependencies through interfaces. Leverage build tools to automate modular builds, integration testing, and deployment processes.

Implement strong cohesion within modules through related classes with shared responsibilities. Colocate logically connected classes while distributing responsibilities across modules. Group helper classes and utilities as internal details in containing modules rather than stand-alone modules. Leverage object-oriented features like inheritance, polymorphism and composition for loose coupling and flexibility within well-defined module boundaries.

Ensure consistency between logical module boundaries defined at design time and physical packaging for implementation and deployment. Use language-specific module system features like packages, namespaces, JAR files etc. to cleanly separate deployable modules. Verify runtime instantiation and wiring matches logical design intent through testing.

Add documentation for modules describing purpose, public interfaces, dependencies and versioning approach. Draft module life cycle contracts covering initialization, configuration, access, disposal etc. Include support for extension, customization, replacement through defining extension points. Abstract implementation details behind interfaces and follow semantic versioning practices during evolution and upgrades.

Perform regular testing and reviews to ensure module interfaces remain narrow, stable and hide complexity over time as requirements change. Minimize modification to existing module functionality through extension mechanisms. Gradually refactor monolithic modules by splitting responsibilities into sub-modules as complexity grows. Leverage logging, monitoring and instrumentation to verify loose coupling and understand dependencies at runtime.

With proper planning and care during software design and implementation, modules can be assembled into a cohesive yet flexible application architecture. Effective module integration is a key practice for developing reusable, evolvable and maintainable systems at scale over the long term. Regular reviews help ensure the benefits are realized by aligning design with implementation through the project life cycle.