AP CSA 3.4 FRQ Practice: Two Ways to Build

Unit 3: Class Creation · Lesson 3.4 · FRQ Practice

Two Ways to Build

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 3.4 pageAll Unit 3 lessons

Why this question is worth four points

A constructor has no return type. Give it one and it silently becomes an ordinary method with the same name as the class, the compiler accepts it, every object is built by the default constructor instead, and every field is 0 or null. There is no error message anywhere in that sentence, which is why it is worth a question of its own.

What you are given

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

The question

  1. (a) A constructor Ticket(String event, int price) that stores both.
  2. (b) A constructor Ticket(String event) that stores the event with a price of 10.
  3. (c) public String getEvent() and public int getPrice() return what was stored.
  4. (d) public String describe() returns the event, a space, then the price.

What the reader is looking for

  1. Write class Ticket with the two constructors and the methods described. No main method.
  2. The one argument constructor should call the two argument one rather than repeating the assignments. this(event, 10); is how, and it must be the first statement.
  3. A constructor is named exactly like the class and has NO return type, not even void.

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
Concert 45 Matinee
Example 1 output
Concert
45
Concert 45
10
Matinee 10
Example 2 input
Gala 10 Preview
Example 2 output
Gala
10
Gala 10
10
Preview 10

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
public void Ticket(String event, int price) is NOT a constructor. It is a method that happens to share the name of the class, and every object then gets built by the invisible default constructor with all fields at 0 and null.

    
Hint 2
this(event, 10); calls your other constructor. It has to be the very first statement in the body.

    
Hint 3
The driver builds both kinds of Ticket. A one argument constructor that forgets the default price prints 0 rather than 10.



  
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.

    
    
      
  • the one argument constructor forgets the default price
    • 
      
  • the two argument constructor shadows its own fields
    • 
      
  • describe omits the separating space
    • 
      
  • the default price is 1 rather than 10
    • 
    

  


  
Where to go next

  

    Rework the Lesson 3.4 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
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