Why do you have to 'extend activity' in Android development?

When you create a new class, why must you alway开发者_运维知识库s say for example:

class Main extends Activity { ... }

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You don't. When you create a new Activity, it must extends Activity, but you may create any other class as well.

Extending Activity gives you the ready-made UI and resources management and allows the zigote to instantiate you as a GUI application.