How is the user interface output implemented in the system?

In Android, the user interface (UI) rendering is carried out through a hierarchy of Views, which are built from elements such as buttons, text fields, images, and containers.

The main stages of UI rendering:

1. Layout — the UI is described in XML files or created programmatically, forming a tree of Views.
2. Inflation — the XML layout is converted into View objects using LayoutInflater.
3. Drawing — the system calls methods onMeasure(), onLayout(), and onDraw() to calculate sizes, position, and visually display each View.
4. Display on screen — the constructed View tree is rendered on the device's screen.

For example, when an Activity is launched, the setContentView() method is called, which loads the layout and begins the process of building and displaying the interface.