AP CSA 1.15 FRQ Practice: Split a Record Line

Unit 1: Using Objects and Methods · Lesson 1.15 · FRQ Practice

Split a Record Line

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 1.15 pageAll Unit 1 lessons

Why this question is worth four points

substring and indexOf together are the most heavily tested pair in Unit 1, and the exam always tests the same boundary: substring(a, b) includes a and EXCLUDES b. Off by one here is not a typo, it is the whole question.

What you are given

One variable is declared and assigned for you: String record, which always contains exactly one comma, with at least one character on each side of it.

The question

  1. (a) Print the position of the comma.
  2. (b) Print everything before the comma.
  3. (c) Print everything after the comma.
  4. (d) Print the total number of characters that are not the comma.

What the reader is looking for

  1. Write a code segment that prints four lines in rubric order.
  2. Neither part (b) nor part (c) may include the comma itself. substring(0, i) stops just before index i, and substring(i + 1) starts just after it.
  3. The precondition guarantees there is exactly one comma, so part (d) is the length minus one.

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 is given
String record = "Smith,Alice";
Example 1 output
5
Smith
Alice
10
Example 2 is given
String record = "A,longer second part";
Example 2 output
1
A
longer second part
19

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
substring(0, at) gives characters 0 through at - 1, which is everything before the comma and not the comma. Using at + 1 as the end includes it.

    
Hint 2
The one argument form, substring(at + 1), runs to the end of the String. There is no need to pass length() as a second argument, though it is not wrong to.

    
Hint 3
Store indexOf once. Parts (a), (b) and (c) all need the same position, and calling indexOf three times is three chances to write one of them differently.



  
Before you submit

  
2 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 (b) includes the comma, the classic substring off-by-one
    • 
      
  • part (c) starts AT the comma instead of after it
    • 
    

  


  
Where to go next

  

    Rework the Lesson 1.15 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
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