AP Computer Science A Full-length practice exam 2 — Free with Answer Explanations

Question 1

A student writes the following method to count elements equal to a target value in a 2D array:

public static int count(int[][] arr, int target) {
    int cnt = 0;
    for (int r = 0; r < arr.length; r++) {
        for (int c = 0; c < arr[0].length; c++) {
            if (arr[r][c] == target) cnt++;
        }
    }
    return cnt;
}

For which input would this method produce incorrect results?

A.A 3×3 array with target 7B.A 1×1 array with target 0C.A jagged array where row 1 has more columns than row 0D.A 4×4 array with target -1

Question 2

What is the output of the following code?

int[][] g = new int[2][3];
for (int r = 0; r < g.length; r++) {
    for (int c = 0; c < g[r].length; c++) {
        g[r][c] = r + c;
    }
}
System.out.println(g[1][2]);

A.0B.2C.3D.5

Question 3

Given the following classes:

public class Animal {
    public String speak() { return "..."; }
}
public class Dog extends Animal {
    public String speak() { return "Woof"; }
}

What does the following print?

Animal a = new Dog();
System.out.println(a.speak());

A....B.WoofC.Compile error: cannot assign Dog to Animal variableD....Woof

Question 4

What is the output of the following code?

int n = 100;
int count = 0;
while (n > 1) {
    n /= 2;
    count++;
}
System.out.println(count);

A.5B.6C.7D.100

Question 5

What is printed by the following code?

double d = 1.0 / 3.0;
int i = (int)(d * 10);
System.out.println(i);

A.3B.4C.3.3D.0

Question 6

Consider the following hierarchy:

public class Vehicle { public void move() { System.out.println("Vehicle moves"); } }
public class Boat extends Vehicle { public void move() { System.out.println("Boat sails"); } }
public class AmphibiousVehicle extends Boat { }

What is printed by:

Vehicle v = new AmphibiousVehicle();
v.move();

A.Vehicle movesB.Boat sailsC.Vehicle movesBoat sailsD.Compile error: AmphibiousVehicle does not define move()

Question 7

What is the output of the following code?

int[] arr = {5, 10, 15, 20};
System.out.println(arr.length);
System.out.println(arr[2]);

A.4\n15B.4\n20C.3\n15D.4\n10

Question 8

Which of the following correctly demonstrates the use of equals() from the Object class, and when would you override it?

public class Point {
    int x, y;
    public Point(int x, int y) { this.x = x; this.y = y; }
}
Point p1 = new Point(2, 3);
Point p2 = new Point(2, 3);
System.out.println(p1.equals(p2));

A.Prints true because p1 and p2 have the same x and y values.B.Prints false; to get true, Point must override equals() to compare x and y.C.Causes a compile error because equals() cannot be called on user-defined classes.D.Prints true only if the two objects were created in the same statement.

Question 9

A programmer writes:

public class Printer {
    public void print(String s) { System.out.println(s); }
    public void print(int n) { System.out.println(n * 2); }
}
Printer p = new Printer();
p.print(5);

What is the output, and what concept does this demonstrate?

A.Prints 5; demonstrates method overriding.B.Compile error: two methods cannot have the same name.C.Prints 10; demonstrates method overloading.D.Prints 5; demonstrates polymorphism through inheritance.

Question 10

Consider the following class hierarchy:

public class Vehicle {
    private String brand;
    public Vehicle(String brand) { this.brand = brand; }
    public String getBrand() { return brand; }
}
public class Car extends Vehicle {
    private int doors;
    public Car(String brand, int doors) {
        super(brand);
        this.doors = doors;
    }
}

Which statement about Car's constructor is true?

A.It will cause a compile error because Car does not declare the brand field.B.The super(brand) call must be the last statement in the constructor.C.It correctly delegates brand initialization to the Vehicle constructor via super().D.Without a no-arg constructor in Vehicle, this code will not compile.

Question 11

What is the output of the following code?

ArrayList<Integer> list = new ArrayList<>();
list.add(100);
list.add(200);
list.set(0, 999);
System.out.println(list.get(0));
System.out.println(list.size());

A.999\n2B.999\n3C.100\n2D.100\n3

Question 12

What does the following method return when called with mystery(5)?

public static int mystery(int n) {
    if (n == 1) return 0;
    return 1 + mystery(n / 2);
}

A.2B.3C.5D.1

Question 13

What is the output of the following code?

String s = "Java";
s = s.toUpperCase();
s = s + " rocks";
System.out.println(s);

A.Java rocksB.JAVA rocksC.JAVA ROCKSD.java rocks

Question 14

What is the output of the following code?

ArrayList<Double> list = new ArrayList<>();
list.add(1.5);
list.add(2.5);
list.add(3.5);
double sum = 0;
for (double d : list) {
    sum += d;
}
System.out.println(sum);

A.7.5B.6.0C.Compile error: cannot use double in enhanced for with ArrayListD.7.0

Question 15

What is printed by the following code?

public class Temp {
    private double celsius;
    
    public Temp(double c) { celsius = c; }
    
    public double toFahrenheit() {
        return celsius * 9 / 5 + 32;
    }
    
    public String toString() {
        return celsius + "C";
    }
}

// In main:
Temp t = new Temp(100);
System.out.println(t);
System.out.println(t.toFahrenheit());

A.Temp@[hashcode]\n212.0B.100.0C\n212.0C.100C\n212.0D.100.0C\n180.0

Question 16

What is the result of the following expression in Java?

int result = 3 + 4 * 2 - 10 / 4;

A.8B.9C.5D.12

Question 17

What happens when the following code executes?

int[] arr = new int[3];
System.out.println(arr[0]);
arr[5] = 10;

A.0 is printed, then ArrayIndexOutOfBoundsException is thrown.B.0 is printed, and arr[5] is set to 10.C.NullPointerException is thrown on line 2.D.Compile error: arr[5] is out of bounds.

Question 18

What is the output of the following code?

int[] nums = {3, 1, 4, 1, 5};
int max = nums[0];
for (int n : nums) {
    if (n > max) {
        max = n;
    }
}
System.out.println(max);

A.3B.5C.1D.4

Question 19

What is the output of the following code?

ArrayList<Integer> list = new ArrayList<>();
for (int i = 1; i <= 5; i++) {
    list.add(i);
}
for (int i = 0; i < list.size(); i++) {
    System.out.print(list.get(i) + " ");
}

A.1 2 3 4 5B.0 1 2 3 4C.1 2 3 4D.2 3 4 5 6

Question 20

What is the output of the following code?

String[] words = {"cat", "bird", "ant", "dog"};
String first = words[0];
for (String w : words) {
    if (w.compareTo(first) < 0) {
        first = w;
    }
}
System.out.println(first);

A.catB.antC.dogD.bird

Question 21

What is the output of the following code?

public class Counter {
    private int count;
    
    public Counter(int start) {
        count = start;
    }
    
    public Counter add(int n) {
        count += n;
        return this;
    }
    
    public int getCount() { return count; }
}

// In main:
Counter c = new Counter(0);
System.out.println(c.add(3).add(4).getCount());

A.3B.7C.Compile error: add returns Counter, not void.D.4

Question 22

What is the output of the following code?

int x = 4;
if (x % 2 == 0)
    System.out.println("even");
    System.out.println("positive");

A.evenB.even\npositiveC.positiveD.Compile error

Question 23

What is the output of the following code?

int[][] m = {{2, 4}, {6, 8}};
for (int r = 0; r < m.length; r++) {
    for (int c = 0; c < m[r].length; c++) {
        System.out.print(m[r][c] + " ");
    }
}

A.2 6 4 8B.2 4 6 8C.8 6 4 2D.4 8 2 6

Question 24

What is the output of the following code?

int a = 2;
System.out.println(a++);
System.out.println(a);

A.2\n3B.3\n3C.2\n2D.3\n4

Question 25

What is the output of the following code?

public static void mystery(int n) {
    if (n <= 0) return;
    mystery(n - 1);
    System.out.println(n);
}
// Called with:
mystery(3);

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

Question 26

What is the output of the following code?

ArrayList<Integer> a = new ArrayList<>();
a.add(1); a.add(2); a.add(3);
ArrayList<Integer> b = new ArrayList<>(a);
b.add(4);
System.out.println(a.size());
System.out.println(b.size());

A.4\n4B.3\n4C.3\n3D.4\n3

Question 27

What is the output of the following code?

import java.util.ArrayList;
ArrayList<Integer> list = new ArrayList<>();
list.add(10);
list.add(20);
list.add(30);
System.out.println(list.size());
System.out.println(list.get(1));

A.3\n20B.3\n10C.2\n20D.3\n30

Question 28

What is the output of the following code?

public class Student {
    private String name;
    private int grade;
    
    public Student(String name, int grade) {
        this.name = name;
        this.grade = grade;
    }
    
    public void setGrade(int grade) {
        if (grade >= 0 && grade <= 100) {
            this.grade = grade;
        }
    }
    
    public int getGrade() { return grade; }
}

// In main:
Student s = new Student("Ali", 85);
s.setGrade(110);
System.out.println(s.getGrade());

A.110B.85C.0D.Compile error

Question 29

What is the output of the following code?

public class Counter {
    private int count = 0;
    
    public void increment() {
        count++;
    }
    
    public int getCount() {
        return count;
    }
}

// In main:
Counter c = new Counter();
c.increment();
c.increment();
c.increment();
System.out.println(c.getCount());

A.0B.3C.1D.Compile error: count is private.

Question 30

What value does the following method return when called with sum(4)?

public static int sum(int n) {
    if (n == 0) return 0;
    return n + sum(n - 1);
}

A.4B.8C.10D.24

Question 31

What is the output of the following code?

ArrayList<Integer> list = new ArrayList<>();
for (int i = 0; i < 5; i++) {
    list.add(i * 2);
}
list.remove(Integer.valueOf(4));
System.out.println(list);

A.[0, 2, 6, 8]B.[0, 2, 4, 6, 8]C.[0, 2, 4, 8]D.[0, 2, 4, 6]

Question 32

What is the output of the following code?

int[] arr = {5, 3, 8, 1, 9};
int target = 8;
int index = -1;
for (int i = 0; i < arr.length; i++) {
    if (arr[i] == target) {
        index = i;
    }
}
System.out.println(index);

A.2B.8C.-1D.3

Question 33

Which of the following correctly compares two String objects for equal content in Java?

String a = "hello";
String b = "hello";

A.if (a == b)B.if (a.equals(b))C.if (a.compareTo(b) == true)D.if (String.equals(a, b))

Question 34

What is the output of the following code?

for (int i = 0; i < 5; i++) {
    if (i % 2 == 0) continue;
    System.out.print(i + " ");
}

A.0 2 4B.1 3C.0 1 2 3 4D.1 2 3 4

Question 35

Which boolean expression correctly checks whether x is between 1 and 10 (inclusive)?

A.1 <= x <= 10B.x >= 1 && x <= 10C.x >= 1 || x <= 10D.!(x < 1 && x > 10)

Question 36

Which of the following recursive methods contains a flaw that would cause infinite recursion for the call badRecurse(5)?

// Option A
public static int badRecurse(int n) {
    if (n == 0) return 0;
    return n + badRecurse(n + 1);
}

A.The base case n == 0 is never reached because each call increases n.B.The base case is missing entirely.C.The method returns the wrong type and will cause a compile error.D.The recursion is fine; badRecurse(5) returns a large positive number.

Question 37

What is the output of the following code?

public class Thing {
    private int x;
    
    public Thing() {
        x = 10;
    }
    
    public Thing(int x) {
        this.x = x;
    }
    
    public int getX() { return x; }
}

// In main:
Thing a = new Thing();
Thing b = new Thing(7);
System.out.println(a.getX() + b.getX());

A.17B.7C.10D.Compile error: duplicate constructor definitions.

Question 38

Which declaration correctly creates a 2D array of integers with 4 rows and 3 columns?

A.int[4][3] arr;B.int arr[4][3];C.int[][] arr = new int[4][3];D.int[][] arr = new int[3][4];

Question 39

What is the output of the following code?

ArrayList<Integer> list = new ArrayList<>();
list.add(1);
list.add(2);
list.add(3);
list.add(4);
for (int i = 0; i < list.size(); i++) {
    if (list.get(i) % 2 == 0) {
        list.remove(i);
    }
}
System.out.println(list);

A.[2, 4]B.[1, 3, 4]C.[1, 3]D.[1, 2, 3]

Question 40

The Fibonacci sequence is defined as fib(0)=0, fib(1)=1, fib(n)=fib(n-1)+fib(n-2) for n≥2. What does the following method return for fib(5)?

public static int fib(int n) {
    if (n == 0) return 0;
    if (n == 1) return 1;
    return fib(n - 1) + fib(n - 2);
}

A.4B.5C.8D.10