AP CSA 3.3 FRQ Practice: Fields, Not Locals

Unit 3: Class Creation · Lesson 3.3 · FRQ Practice

Fields, Not Locals

A free response question in the shape the exam uses: a stated contract, four rubric parts, and no main method handed to you. Worth 4 points.

Back to the Lesson 3.3 pageAll Unit 3 lessons

Why this question is worth four points

The difference between a field and a local variable is the difference between a class that remembers and one that does not, and Java will not warn you which you wrote. A local declared inside a method shadows the field of the same name, the method compiles, and every getter afterwards returns the field it never touched.

What you are given

Nothing is given. Write a class named Locker. Do not write a main method.

The question

  1. (a) A constructor Locker(String owner, int capacity) that stores both.
  2. (b) public String getOwner() and public int getCapacity() return what was stored.
  3. (c) public void store(int items) adds items to what is inside, never letting the contents exceed the capacity.
  4. (d) public int getContents() returns how much is inside, and public int getSpace() returns how much room is left.

What the reader is looking for

  1. Write class Locker with the constructor and methods described. No main method.
  2. A new Locker is empty. Storing more than fits fills it to capacity and discards the rest rather than overflowing.
  3. The contents belong to the object, not to the store method. A count declared inside store is forgotten the moment store returns.

Worked examples

These show what a correct answer prints. There are more cases you cannot see, and they use different values, so an answer built around just these numbers will fail.

Example 1 input
ana 100 30 45
Example 1 output
ana
100
0
30
75
25
Example 2 input
bo 50 40 30
Example 2 output
bo
50
0
40
50
0

Your answer

Main.java

Input for the Run button

How this is scored: your answer runs against every test case, and the fraction it passes becomes your score out of 4. That is not how a human AP reader marks a rubric, so treat the score as a check on whether your code works, and the rubric above as the thing you are actually practising.


  

  
Stuck?

    
Hint 1
The driver calls store TWICE and asks for the contents in between. A store method that keeps its running total in a local variable prints the first amount and then the second amount, never their sum.

    
Hint 2
Declaring int contents = 0; inside store creates a NEW variable that hides the field. It compiles, it runs, and the field stays at 0 forever.

    
Hint 3
getSpace is derived from the capacity and the contents. Storing it as a fourth field means two numbers that can disagree.



  
Before you submit

  
4 mistake(s) that lose points on this question
    
Each of these is a real error the grader catches. Check your answer against them before you submit, not instead of trying.

    
    
      
  • store keeps its total in a local that shadows the field
    • 
      
  • store lets the contents exceed the capacity
    • 
      
  • the constructor never assigns the capacity field
    • 
      
  • getSpace returns the contents rather than the room left
    • 
    

  


  
Where to go next

  

    Rework the Lesson 3.3 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
Get in Touch

  
Whether you're a student, parent, or teacher — I'd love to hear from you.







  
Just want free AP CS resources?

  

    Enter your email below and check the subscribe box — no message needed.
    Students get daily practice questions and study tips. Teachers get curriculum resources and teaching strategies.
  







  
  Typically responds within 24 hours






  
✓

  
Message Sent!

  

    Thanks for reaching out. I'll get back to you within 24 hours.
  







  


  

    
    

    
    

      

        
        
      

      

        
        
      

    


    
    

      

        
        
      

      

        
        
      

    


    
    

      

        
        
      

      

        
        
      

    


    
    

      
🏫 Welcome, fellow educator!

      

        I offer curriculum resources, practice materials, and study guides designed for AP CS teachers.
        Let me know what you're looking for — whether it's classroom materials, a guest speaker,
        or Teachers Pay Teachers resources.
      

    


    
    

      
      
    


    
    

    
    

      
    

  







  

    ✉
    
Email

    
[email protected]

  

  

    📚
    
Courses

    
AP CSA, CSP, & Cybersecurity

  

  

    ⏱
    
Response Time

    
Within 24 hours

  







  Prefer email? Reach me directly at
  [email protected]