AP CSA FRQ Guide
2026 FRQ 2: Bottle
Write a complete Bottle class that tracks the amount of liquid remaining after each use, refilling to capacity whenever a use would drop the amount below 25% of capacity.
Skills Tested
What this FRQ is really practicing
Treat these skills as the study checklist. If any tag feels shaky, review that topic before attempting the full written response.
Starter Approach
How to begin with your own plan
- 1Write the complete class header, instance variables, and constructor. Bottles are filled to capacity when constructed.
- 2Implement updateAmount to subtract amountUsed from the current amount.
- 3Refill the bottle to capacity whenever the updated amount would drop below 25% of capacity, then return the current amount.
Write a first attempt before revealing any solution outline. Most AP CSA FRQ progress comes from tracing your own code and finding the missing case.
Common Mistakes
Mistakes to watch for while writing
Self Check
Review questions before you submit
Uses the correct public class header.
Define the complete Bottle class.
Declares instance variables for capacity and the current amount.
Store both the fixed capacity and the amount that changes over time.
Includes a constructor with a double capacity parameter that fills the bottle.
The starting amount should equal capacity.
Subtracts amountUsed from the current amount.
Update the amount field by subtracting the parameter.
Compares the updated amount to 25% of capacity.
Use 0.25 times capacity as the refill threshold.
Resets the amount to capacity when the threshold is crossed.
Assign capacity back to the amount field inside the if branch.
Returns the current amount after updating.
The method returns a double representing the amount remaining.
Practice Links