AP CSA 4.8 FRQ Practice: Add, Set, Remove

Unit 4: Data Collections · Lesson 4.8 · FRQ Practice

Add, Set, Remove

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 4.8 pageAll Unit 4 lessons

Why this question is worth four points

An ArrayList shifts. add at an index pushes everything right, remove at an index pulls everything left, and set replaces without moving anything. Confusing set with add at the same index changes the size, which is the difference the exam looks for.

What you are given

The driver builds an ArrayList of Integer and passes it to your methods. Write a class named Editor. Do not write a main method.

The question

  1. (a) public static int size(ArrayList list) returns how many elements it holds.
  2. (b) public static void appendTwice(ArrayList list, int value) adds value to the END of the list twice.
  3. (c) public static void replaceFirst(ArrayList list, int value) replaces the element at index 0 without changing the size. Do nothing when the list is empty.
  4. (d) public static int removeLast(ArrayList list) removes and returns the last element, or returns -1 and changes nothing when the list is empty.

What the reader is looking for

  1. Write class Editor with the four static methods described. No main method.
  2. These methods change the list they are GIVEN. An ArrayList is an object, so the caller sees the change.
  3. Part (c) uses set and not add. add at index 0 pushes the old element aside and makes the list longer.

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
3
1 2 3
99
Example 1 output
3
[99, 2, 3]
[99, 2, 3, 99, 99]
99
[99, 2, 3, 99]
Example 2 input
0
7
Example 2 output
0
[]
[7, 7]
7
[7]

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
set(0, value) replaces. add(0, value) inserts. The driver prints the whole list right after, so a size that grew by one is immediately visible.

    
Hint 2
remove(index) returns the element it removed, so part (d) needs no separate get.

    
Hint 3
The last index is size() - 1. Using size() throws IndexOutOfBoundsException.



  
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.

    
    
      
  • part (c) inserts at index 0 instead of replacing, growing the list
    • 
      
  • part (d) removes at size() rather than size() - 1
    • 
      
  • part (b) adds the value only once
    • 
      
  • part (c) forgets to guard the empty list
    • 
    

  


  
Where to go next

  

    Rework the Lesson 4.8 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
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