Classes & Objects – FRQ Practice (AP Computer Science A)

Understanding classes and objects is one of the most important parts of AP Computer Science A. This AP CSA Classes and Objects FRQ Practice page highlights the topics that the College Board regularly tests, including:

• constructors
• instance variables
• accessor/mutator methods
• object behavior
• interaction between objects
• encapsulation and method design

This page contains original, exam-style FRQs with explanations and Java solutions to help students master object-oriented programming.

Why Classes & Objects Matter in AP CSA

Classes and objects form the core of Java programming.
The AP CSA exam expects students to:

• read class definitions
• write constructors
• modify object state
• call methods correctly
• use object references in arrays and ArrayLists

FRQ 1 or FRQ 2 in the exam almost always includes object-oriented logic.

FRQ Practice Problems – AP CSA Classes and Objects FRQ Practice

These practice problems help you apply object-oriented concepts in real exam scenarios. Each problem focuses on constructors, instance variables, method behavior, and object interaction.

The following AP CSA Classes and Objects FRQ Practice questions cover object behavior, encapsulation, and method interactions commonly tested on the AP exam.

FRQ 1 — Constructor & Accessor Behavior

Problem:
Design a Book class with private fields title (String) and pages (int). Write a constructor to initialize both fields and a method isLong() that returns true if pages > 300.

Approach:

• Create private fields
• Write a constructor accepting two parameters
• Return boolean expression based on page count

Solution:

public class Book {
    private String title;
    private int pages;

    public Book(String t, int p) {
        title = t;
        pages = p;
    }

    public boolean isLong() {
        return pages > 300;
    }
}

Common Mistakes:

• Forgetting to initialize both fields
• Using ≥ instead of >
• Accessing fields directly

Mini Summary:
This FRQ reinforces constructor writing, encapsulation, and boolean logic.

FRQ 2 — Mutator Method with Validation

Problem:
A Counter class stores an integer variable count. Write a method increase(int amount) that adds amount to count only if amount > 0.

Approach:

• Validate the argument
• Update the field only when valid
• Ignore invalid input

Solution:

public void increase(int amount) {
    if (amount > 0) {
        count += amount;
    }
}

Common Mistakes:

• Adding negative values
• Returning a value from a void method
• Using the wrong comparison

Mini Summary:
This FRQ tests mutator logic and state modification.

FRQ 3 — Interaction Between Objects

Problem:
A Team object stores two Player objects: p1 and p2.
Write a method totalScore() that returns the sum of both players’ scores using accessor methods.

Approach:

• Call each player’s getScore() method
• Add returned values
• Return the total

Solution:

public int totalScore() {
    return p1.getScore() + p2.getScore();
}

Common Mistakes:

• Accessing private fields directly (p1.score)
• Forgetting method calls
• Returning one player’s score instead of both

Mini Summary:
This FRQ focuses on object references and calling methods on other objects.

FRQ 4 — Overriding toString()

Problem:
A Point class stores integers x and y. Write a toString() method that returns the point in the format "(x, y)".

Approach:

• Override toString()
• Use correct formatting
• Return a String instead of printing

Solution:

public String toString() {
    return "(" + x + ", " + y + ")";
}

Common Mistakes:

• System.out.println instead of return
• Missing parentheses
• Incorrect spacing

Mini Summary:
This FRQ reinforces method overriding and formatted string creation.

FRQ 5 — Class with Computation Method

Problem:
Create a Temperature class with a private field double celsius. Write a constructor that initializes it, and a method toFahrenheit() that returns (celsius * 9/5) + 32.

Approach:

• Store Celsius internally
• Convert using correct floating-point arithmetic
• Return the computed value

Solution:

public class Temperature {
    private double celsius;

    public Temperature(double c) {
        celsius = c;
    }

    public double toFahrenheit() {
        return (celsius * 9.0 / 5) + 32;
    }
}

Common Mistakes:

• Using integer division (9/5 = 1)
• Printing instead of returning
• Returning int instead of double

Mini Summary:
This FRQ checks constructor skills and mathematical computation inside classes.

Skills Reinforced on This Page

• Class design & encapsulation
• Writing constructors
• Using accessors and mutators
• Object interaction
• Method construction
• State changes
• Computation using instance variables

Related FRQ Pages

• Arrays – FRQ Practice
• ArrayList – FRQ Practice
• Strings – FRQ Practice
• 2D Arrays – FRQ Practice
• Inheritance & Polymorphism – FRQ Practice (Coming Soon)
• Mixed Topic FRQs (Coming Soon)
• Mock FRQ Sets (Coming Soon)

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Official Resource

For official exam information, visit:
https://apcentral.collegeboard.org/courses/ap-computer-science-a