AP CSA Unit 3 Practice Exam: Class Creation (Part 1)

Unit 3: Class Creation

Part 1: Questions 1-25

Class Structure • Instance Variables • Constructors • The this Keyword

New AP CSA Curriculum (2025-2026): This exam covers Unit 3 (Class Creation) - designing classes, constructors, instance variables, methods, encapsulation, and static vs instance members. This is Part 1 of 2.

0 Correct | 0 Incorrect | 0/25 Answered

Class Structure & Instance Variables (Questions 1-12)

Question 1

Which access modifier should be used for instance variables to properly implement encapsulation?

A) public
B) private
C) protected
D) No modifier needed

Encapsulation means hiding internal data. Instance variables should be private so they can only be accessed through methods (getters/setters) that you control.

Question 2

What is the default value of count when a Dog object is created?

public class Dog {
    private String name;
    private int age;
    private int count;
}

A) 0
B) null
C) undefined
D) Compile error - must initialize

Instance variables get default values automatically. For int, the default is 0. For objects like String, it is null. For boolean, it is false.

Question 3

What is printed when this code runs?

public class Student {
    private String name;
    private double gpa;
    
    public void printInfo() {
        System.out.println(name + " " + gpa);
    }
}

// In main method:
Student s = new Student();
s.printInfo();

A) Compile error
B) null 0.0
C) "" 0.0
D) NullPointerException

String defaults to null, double defaults to 0.0. When concatenating null with a String, Java converts it to the text "null", so the output is: null 0.0

Question 4

Which statement correctly describes instance variables?

A) They are shared among all objects of the class
B) They must be declared inside methods
C) Each object has its own copy of instance variables
D) They cannot be private

Instance variables belong to each individual object. If you create two Dog objects, each has its own name and age. Static variables are shared among all objects.

Question 5

What is the best practice concern with this class?

public class Circle {
    public double radius;
    
    public double getArea() {
        return 3.14159 * radius * radius;
    }
}

A) getArea() should be private
B) radius must be initialized in declaration
C) Nothing is wrong
D) radius should be private for encapsulation

While this compiles, radius being public violates encapsulation. Anyone can set it to invalid values (like -5). Making it private with a setter allows validation.

Question 6

What is printed?

public class Counter {
    private int value;
    
    public void increment() { value++; }
    public int getValue() { return value; }
}

// In main:
Counter c1 = new Counter();
Counter c2 = new Counter();
c1.increment();
c1.increment();
c2.increment();
System.out.println(c1.getValue() + " " + c2.getValue());

A) 3 3
B) 2 2
C) 1 2
D) 2 1

Each Counter has its own value. c1 is incremented twice (value=2), c2 once (value=1). They are independent objects.

Question 7

What is the default value of isActive when an Account object is created?

public class Account {
    private String owner;
    private double balance;
    private boolean isActive;
}

A) true
B) null
C) false
D) Compile error

Default value for boolean instance variables is false. Remember: int to 0, double to 0.0, boolean to false, objects to null.

Question 8

Which line causes a compile error?

public class BankAccount {
    private double balance;
    public double getBalance() { return balance; }
}

// In a separate class:
public class Main {
    public static void main(String[] args) {
        BankAccount acct = new BankAccount();
        double x = acct.balance;      // Line A
        double y = acct.getBalance(); // Line B
    }
}

A) Line B only
B) Line A only
C) Both lines
D) Neither line

Line A directly accesses balance, which is private. Private members cannot be accessed outside the class. Line B uses the public getter, which is allowed.

Question 9

What does this code print?

public class Point {
    private int x, y;
    
    public void setLocation(int newX, int newY) {
        x = newX;
        y = newY;
    }
    
    public String toString() {
        return "(" + x + ", " + y + ")";
    }
}

// In main:
Point p = new Point();
p.setLocation(5, 10);
System.out.println(p);

A) (0, 0)
B) null
C) (5, 10)
D) Point@1a2b3c

When you print an object, Java calls its toString() method. After setLocation(5, 10), x=5 and y=10, so it returns "(5, 10)".

Question 10

What is the scope of the instance variable name?

public class Person {
    private String name;
    
    public void greet() {
        String greeting = "Hello, " + name;
        System.out.println(greeting);
    }
}

A) Only within the greet() method
B) Only within constructors
C) Accessible from any class
D) Throughout the entire Person class

Instance variables have class scope - accessible by any method in the class. Local variables (like greeting) only exist within their method.

Question 11

What happens when you compile this code?

public class Rectangle {
    private int width, height;
    
    public int getArea() {
        int result;
        result = width * height;
        return result;
    }
}

A) Compile error - result not initialized
B) Compiles successfully
C) Compile error - width/height not initialized
D) Runtime error

This compiles fine. result is assigned before use. Instance variables (width, height) get default values automatically. Local variables must be assigned before reading.

Question 12

Which represents a "has-a" relationship (composition)?

// Option 1:
public class Car {
    private Engine engine;
}

// Option 2:
public class Car extends Engine { }

A) Option 1 shows "has-a"
B) Option 2 shows "has-a"
C) Both show "has-a"
D) Neither shows "has-a"

Option 1 shows composition ("has-a"): a Car has an Engine as an instance variable. Option 2 shows inheritance ("is-a"), which is illogical here - a Car is not a type of Engine.

Constructors (Questions 13-25)

Question 13

What is printed?

public class Book {
    private String title;
    private int pages;
    
    public Book(String t, int p) {
        title = t;
        pages = p;
    }
    
    public void print() {
        System.out.println(title + ": " + pages);
    }
}

// In main:
Book b = new Book("Java", 500);
b.print();

A) null: 0
B) t: p
C) Compile error
D) Java: 500

The constructor assigns parameters to instance variables: title="Java", pages=500. The print method outputs "Java: 500".

Question 14

What is the result of this code? (Look carefully at the constructor!)

public class Cat {
    private String name;
    
    public Cat(String name) {
        name = name;  // Bug here!
    }
    
    public String getName() { return name; }
}

// In main:
Cat c = new Cat("Whiskers");
System.out.println(c.getName());

A) null
B) Whiskers
C) Compile error
D) name

Common bug! name = name assigns the parameter to itself. The instance variable is never set, so it stays null. Fix: use this.name = name;

Question 15

What is the result with the fixed constructor using this?

public class Cat {
    private String name;
    
    public Cat(String name) {
        this.name = name;  // Fixed!
    }
    
    public String getName() { return name; }
}

// In main:
Cat c = new Cat("Whiskers");
System.out.println(c.getName());

A) null
B) this.name
C) Compile error
D) Whiskers

Using this.name refers to the instance variable, while name alone refers to the parameter. Now the instance variable is correctly set to "Whiskers".

Question 16

What happens when this code runs?

public class Employee {
    private String name;
    private double salary;
    
    public Employee(String n, double s) {
        name = n;
        salary = s;
    }
}

// In main:
Employee e = new Employee();

A) Creates employee with null name and 0.0 salary
B) Creates empty employee
C) Compile error - no matching constructor
D) Runtime error

When you write ANY constructor, Java no longer provides the default no-argument constructor. Since only a 2-parameter constructor exists, new Employee() causes a compile error.

Question 17

What is printed? (Constructor overloading)

public class Product {
    private String name;
    private double price;
    
    public Product() {
        name = "Unknown";
        price = 0.0;
    }
    
    public Product(String n, double p) {
        name = n;
        price = p;
    }
    
    public void print() {
        System.out.println(name + ": $" + price);
    }
}

// In main:
Product p1 = new Product();
Product p2 = new Product("Widget", 9.99);
p1.print();
p2.print();

A) Unknown: $0.0 then Widget: $9.99
B) null: $0.0 then Widget: $9.99
C) Compile error
D) Widget: $9.99 then Unknown: $0.0

Constructor overloading means multiple constructors with different parameter lists. p1 uses the no-arg constructor (name="Unknown", price=0.0); p2 uses the parameterized one (name="Widget", price=9.99).

Question 18

Which statement about constructors is FALSE?

A) Constructors must have the same name as the class
B) A class can have multiple constructors
C) Constructors are called with the new keyword
D) Constructors can have a return type of void

Constructors do NOT have a return type - not even void. If you write public void ClassName(), that is a regular method, not a constructor!

Question 19

What is printed? (Constructor chaining with this())

public class Timer {
    private int seconds;
    
    public Timer() {
        this(0);
    }
    
    public Timer(int s) {
        seconds = s;
    }
    
    public int getSeconds() { return seconds; }
}

// In main:
Timer t = new Timer();
System.out.println(t.getSeconds());

A) Compile error
B) 0
C) null
D) StackOverflowError

this(0) calls another constructor in the same class. The no-arg constructor calls the one-arg with 0. seconds=0. This is called constructor chaining.

Question 20

What is wrong with this constructor?

public class Game {
    private int score;
    
    public Game(int s) {
        System.out.println("Starting");
        this(0);  // Problem here
        score = s;
    }
    
    public Game() { score = 0; }
}

A) Cannot call this() in a constructor
B) Nothing is wrong
C) this() must be the first statement
D) Cannot have two constructors

When calling another constructor with this(), it MUST be the very first statement. The println before this(0) causes a compile error.

Question 21

What does this refer to in a method?

public class Car {
    private String model;
    
    public Car(String model) {
        this.model = model;
    }
    
    public void compare(Car other) {
        if (this == other) {
            System.out.println("Same car!");
        }
    }
}

A) The current object the method was called on
B) The class Car itself
C) The parameter being passed in
D) A new instance of the class

this is a reference to the current object - the instance on which the method was invoked. In myCar.compare(other), this refers to myCar.

Question 22

What is printed?

public class Box {
    private int size;
    
    public Box() {
        this(10);
        size = size + 5;
    }
    
    public Box(int s) { size = s; }
    
    public int getSize() { return size; }
}

// In main:
Box b = new Box();
System.out.println(b.getSize());

A) 15
B) 10
C) 5
D) 0

No-arg calls this(10), setting size=10. Then size=size+5=15. Constructor chaining happens first, then remaining code executes.

Question 23

How many times is the constructor called?

public class Item {
    private static int count = 0;
    
    public Item() { count++; }
    
    public static int getCount() { return count; }
}

// In main:
Item a = new Item();
Item b = new Item();
Item c = a;
System.out.println(Item.getCount());

A) 1
B) 3
C) 0
D) 2

new Item() is called twice (for a and b). Item c = a just copies the reference - no new object created, constructor not called. count=2.

Question 24

What is the primary purpose of a constructor?

public class Student {
    private String name;
    private int id;
    private double gpa;
    
    public Student(String name, int id) {
        this.name = name;
        this.id = id;
        this.gpa = 0.0;
    }
}

A) To destroy the object
B) To initialize the object's state
C) To declare instance variables
D) To return the object

Constructors initialize the state of a new object. They set instance variables to starting values, from parameters or defaults like gpa=0.0.

Question 25

What is printed?

public class Temperature {
    private double celsius;
    
    public Temperature(double fahrenheit) {
        celsius = (fahrenheit - 32) * 5.0 / 9.0;
    }
    
    public double getCelsius() { return celsius; }
}

// In main:
Temperature t = new Temperature(32);
System.out.println(t.getCelsius());

A) 0.0
B) 32.0
C) 100.0
D) -17.78

The constructor converts F to C: (32-32)*5/9 = 0*5/9 = 0.0. 32 degrees F equals 0 degrees C (the freezing point of water).

Part 1 Complete!

Continue to Part 2 for questions on Methods, Static vs Instance, and more advanced topics.

Continue to Part 2 →

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