What is the core programming language for Android OS app development?

The core programming language for Android OS app development is Java. This is primarily because Android was originally developed using Java, and it provides the necessary libraries and frameworks that developers need to create robust Android applications. Java offers a structured approach to programming, which is essential for building complex applications. It also has extensive community support and a wide range of development tools and libraries that facilitate app development.

While other languages like Swift, Ruby, and Python are widely used for various types of programming, they are not the foundational languages for Android development. Swift is specifically designed for iOS app development; Ruby is often used for web development, and Python is known for its versatility in many programming domains but lacks the native support for Android app development as Java does. Thus, Java stands out as the primary and most supported language for building Android applications.