A programmer needs to instruct an object to move up when the up-arrow key is pressed. Which of the following must the programmer write to accomplish this?

A programmer needs to instruct an object to move up when the up-arrow key is pressed. Which of the following must the programmer write to accomplish this?

• A. A for loop
• B. A class definition
• C. A constant declaration
• D. An event-handler

Answer: (D)

Responding to user input from the keyboard is an event-driven action. To move the object when the up-arrow key is pressed, you need something that runs in response to that specific input. An event-handler is designed to run a block of code when a particular event occurs, like the up-arrow key being pressed. Inside that handler you would update the object's vertical position (for example, decreasing its y-coordinate by a speed value) and redraw, so the movement happens precisely in response to the key press. A for loop repeats a block a set number of times, not in reaction to user actions. A class definition describes a type of object and its behavior, but by itself it doesn’t respond to input. A constant declaration defines an immutable value, not interactive behavior.

Responding to user input from the keyboard is an event-driven action. To move the object when the up-arrow key is pressed, you need something that runs in response to that specific input. An event-handler is designed to run a block of code when a particular event occurs, like the up-arrow key being pressed. Inside that handler you would update the object's vertical position (for example, decreasing its y-coordinate by a speed value) and redraw, so the movement happens precisely in response to the key press.

A for loop repeats a block a set number of times, not in reaction to user actions. A class definition describes a type of object and its behavior, but by itself it doesn’t respond to input. A constant declaration defines an immutable value, not interactive behavior.