Final answer:
The event source notifies all associated event listeners when an event occurs. Event listeners are crucial in event-driven programming, allowing for modular and maintainable code.
Step-by-step explanation:
Event-driven programming is a paradigm where the flow of the program is determined by events such as user actions, sensor outputs, or message passing from other programs. In this paradigm, event listeners are crucial components. When a specific event occurs, the source object of that event will go through the list of registered listeners and notify them by calling their event-handling methods.
For example, in a graphical user interface (GUI), when a user clicks a button, the button (event source) will notify the event listener associated with the click, which might in turn initiate the appropriate response programmed by a developer. This pattern allows for a clean separation of concerns and makes the code more modular and easier to maintain.