How is navigation within a single Activity implemented in applications?

Navigation within a single Activity in Android applications is usually implemented using fragments. Instead of launching a new Activity for each screen, you can dynamically replace or add fragments within a single Activity, allowing smooth transitions between different interfaces.

Main implementation methods:

• Using FragmentManager to add, replace, and remove fragments.
• Using the Navigation Component — a modern tool from Google that simplifies navigation and stack management of fragments.

Example of replacing a fragment:

supportFragmentManager.beginTransaction()
    .replace(R.id.fragment_container, NewFragment())
    .addToBackStack(null) // so you can go back
    .commit()

This approach helps save resources and creates a smoother user experience.