What is a key Event and what is it used for?

A key event is called whenever the user of your application presses a key on their keyboard. For example, let's assume you are building a video game and you want the player to move forward when they press "W". You can handle this by moving the player forward when a keyDown event is called for that key. Usually, the library or framework you are working with handles this and allows you to implement your own key handler for your own functionality.

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