What characteristic of events allows event handlers to be triggered at random times?

The characteristic that allows event handlers to be triggered at random times is that events are asynchronous in nature. Asynchronous events operate independently of the main program flow, meaning they can occur at unpredictable times without waiting for the current execution to finish. For example, user actions like clicks or keyboard inputs can happen at any moment, triggering the associated event handlers when they occur. This nature of events allows for a more dynamic and responsive application, as event handlers can respond to user actions or other external stimuli whenever they happen, rather than being tied to specific points in the code execution sequence.

In contrast, user-initiated events may seem to suggest randomness, but they are still dependent on user actions. Additionally, synchronous events do not allow for this flexibility, as they require the execution to wait for the event to complete before moving on. Similarly, events that must be explicitly called by the program do not have the spontaneous aspect that asynchronous events possess. Thus, the asynchronous characteristic is key to enabling event handlers to trigger at random times in a program.