What are the SOLID principles and how are they applicable in Android development?

The SOLID principles are a set of five fundamental object-oriented design rules aimed at creating flexible, maintainable, and extendable code:

• S (Single Responsibility Principle) — a class should have only one reason to change.
• O (Open/Closed Principle) — software entities should be open for extension but closed for modification.
• L (Liskov Substitution Principle) — objects of a superclass should be replaceable with objects of subclasses without affecting correctness.
• I (Interface Segregation Principle) — clients should not be forced to depend on interfaces they do not use.
• D (Dependency Inversion Principle) — depend on abstractions, not on concrete implementations.

In Android development, applying SOLID helps:

• Separate UI logic from business logic (e.g., through MVVM or MVP architectures).
• Create modular and testable code.
• Simplify maintenance and extension of the application.

Example: an Activity class should only handle display and user interaction (SRP), while business logic should be moved to ViewModel or Presenter. This facilitates testing and reusing code.