Unit 4 Practice Exam: 2D Arrays & Additional Topics

Unit 4: 2D Arrays & Additional Topics

50 Questions • AP Exam Difficulty

2D Arrays • Inheritance • Polymorphism • Recursion • Searching & Sorting

0 Correct | 0 Incorrect | 0/50 Answered

2D Array Basics (Questions 1-12)

Question 1

What is printed?

int[][] arr = new int[3][4]; System.out.println(arr.length + " " + arr[0].length);

A) 3 4
B) 4 3
C) 12 12
D) 3 3

Question 2

What is printed?

int[][] arr = {{1, 2, 3}, {4, 5, 6}}; System.out.println(arr[1][2]);

A) 2
B) 5
C) 6
D) 3

Question 3

What is printed?

int[][] arr = new int[2][3]; System.out.println(arr[0][0]);

A) null
B) 0
C) 2
D) ArrayIndexOutOfBoundsException

Question 4

How many total elements are in this array?

int[][] arr = {{1, 2}, {3, 4, 5}, {6}};

A) 3
B) 6
C) 9
D) Compile error - rows must be same length

Question 5

What is printed?

int[][] grid = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}; int sum = 0; for (int row = 0; row < grid.length; row++) { for (int col = 0; col < grid[row].length; col++) { sum += grid[row][col]; } } System.out.println(sum);

A) 9
B) 45
C) 15
D) 36

Question 6

What is printed?

int[][] arr = {{1, 2, 3}, {4, 5, 6}}; for (int[] row : arr) { for (int val : row) { System.out.print(val + " "); } }

A) 1 4 2 5 3 6
B) 1 2 3 4 5 6
C) 1 2 4 5
D) Compile error

Question 7

What traversal order does this code use?

for (int col = 0; col < arr[0].length; col++) { for (int row = 0; row < arr.length; row++) { System.out.print(arr[row][col] + " "); } }

A) Row-major order
B) Column-major order
C) Diagonal order
D) Random order

Question 8

What is printed?

int[][] arr = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}; int sum = 0; for (int i = 0; i < arr.length; i++) { sum += arr[i][i]; } System.out.println(sum);

A) 6
B) 12
C) 15
D) 45

Question 9

What is printed?

int[][] arr = {{1, 2, 3}, {4, 5, 6}}; arr[0] = arr[1]; arr[1][0] = 99; System.out.println(arr[0][0]);

A) 1
B) 4
C) 99
D) ArrayIndexOutOfBoundsException

Question 10

What is printed?

String[][] words = {{"A", "B"}, {"C", "D", "E"}}; System.out.println(words[1].length);

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

Question 11

What is printed?

int[][] grid = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}; int count = 0; for (int r = 0; r < grid.length; r++) { for (int c = 0; c < grid[r].length; c++) { if (grid[r][c] % 2 == 0) { count++; } } } System.out.println(count);

A) 4
B) 5
C) 3
D) 9

Question 12

What does this code find?

int max = arr[0][0]; for (int[] row : arr) { for (int val : row) { if (val > max) { max = val; } } }

A) Sum of all elements
B) Maximum value in the 2D array
C) Minimum value in the 2D array
D) Number of rows

Inheritance (Questions 13-24)

Question 13

What keyword is used to inherit from a class?

A) implements
B) extends
C) inherits
D) super

Question 14

What is printed?

public class Animal { public void speak() { System.out.print("Animal"); } } public class Dog extends Animal { public void speak() { System.out.print("Woof"); } } // In main: Animal a = new Dog(); a.speak();

A) Animal
B) Woof
C) AnimalWoof
D) Compile error

Question 15

What is printed?

public class Parent { public Parent() { System.out.print("P "); } } public class Child extends Parent { public Child() { System.out.print("C "); } } // In main: Child c = new Child();

A) C
B) P
C) P C
D) C P

Question 16

What does super() do in a subclass constructor?

A) Calls a method in the superclass
B) Calls the superclass constructor
C) Returns the superclass object
D) Creates a new superclass

Question 17

What is printed?

public class Vehicle { private String type = "Vehicle"; public String getType() { return type; } } public class Car extends Vehicle { private String type = "Car"; } // In main: Car c = new Car(); System.out.println(c.getType());

A) Car
B) Vehicle
C) null
D) Compile error

Question 18

What is method overriding?

A) Same method name with different parameters in same class
B) Subclass provides its own implementation of inherited method
C) Calling a method multiple times
D) Making a method private

Question 19

What is printed?

public class A { public void show() { System.out.print("A"); } } public class B extends A { public void show() { super.show(); System.out.print("B"); } } // In main: B b = new B(); b.show();

A) A
B) B
C) AB
D) BA

Question 20

Can a subclass access private fields of its superclass directly?

A) Yes, always
B) No, must use public/protected getters
C) Only with super keyword
D) Only if in same file

Question 21

What is printed?

public class Shape { public double getArea() { return 0; } } public class Rectangle extends Shape { private int w, h; public Rectangle(int w, int h) { this.w = w; this.h = h; } public double getArea() { return w * h; } } // In main: Shape s = new Rectangle(3, 4); System.out.println(s.getArea());

A) 0
B) 12.0
C) 0.0
D) Compile error

Question 22

What does the Object class provide?

A) It is the root of all class hierarchies
B) Methods like toString() and equals()
C) Every class implicitly extends Object
D) All of the above

Question 23

Which is true about inheritance in Java?

A) A class can extend multiple classes
B) A class can extend only one class
C) Constructors are inherited
D) Private methods are inherited

Question 24

What is printed?

public class Parent { public Parent(int x) { System.out.print("P" + x + " "); } } public class Child extends Parent { public Child() { super(5); System.out.print("C "); } } // In main: Child c = new Child();

A) C P5
B) P5 C
C) Compile error
D) P C

Recursion (Questions 25-36)

Question 25

What is printed?

public static int factorial(int n) { if (n <= 1) return 1; return n * factorial(n - 1); } // In main: System.out.println(factorial(5));

A) 5
B) 15
C) 120
D) 24

Question 26

What are the two essential parts of a recursive method?

A) Loop and return statement
B) Base case and recursive case
C) If statement and else statement
D) Input and output

Question 27

What is printed?

public static void countdown(int n) { if (n <= 0) { System.out.print("Go!"); return; } System.out.print(n + " "); countdown(n - 1); } // In main: countdown(3);

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

Question 28

What is printed?

public static void mystery(int n) { if (n <= 0) return; mystery(n - 1); System.out.print(n + " "); } // In main: mystery(3);

A) 3 2 1
B) 1 2 3
C) 0 1 2 3
D) Nothing prints

Question 29

What is printed?

public static int fib(int n) { if (n <= 1) return n; return fib(n - 1) + fib(n - 2); } // In main: System.out.println(fib(6));

A) 6
B) 8
C) 13
D) 5

Question 30

What happens if a recursive method has no base case?

A) Compile error
B) Returns 0
C) StackOverflowError (infinite recursion)
D) NullPointerException

Question 31

What is printed?

public static int sum(int n) { if (n == 0) return 0; return n + sum(n - 1); } // In main: System.out.println(sum(4));

A) 4
B) 10
C) 24
D) 0

Question 32

What is printed?

public static String reverse(String s) { if (s.length() <= 1) return s; return reverse(s.substring(1)) + s.charAt(0); } // In main: System.out.println(reverse("hello"));

A) hello
B) olleh
C) h
D) o

Question 33

How many times is mystery() called?

public static int mystery(int n) { if (n <= 0) return 0; return 1 + mystery(n - 2); } // In main: mystery(7);

A) 3
B) 4
C) 5
D) 7

Question 34

What is printed?

public static int power(int base, int exp) { if (exp == 0) return 1; return base * power(base, exp - 1); } // In main: System.out.println(power(2, 5));

A) 10
B) 25
C) 32
D) 16

Question 35

What is printed?

public static int gcd(int a, int b) { if (b == 0) return a; return gcd(b, a % b); } // In main: System.out.println(gcd(48, 18));

A) 2
B) 6
C) 12
D) 18

Question 36

What is printed?

public static boolean isPalindrome(String s) { if (s.length() <= 1) return true; if (s.charAt(0) != s.charAt(s.length() - 1)) return false; return isPalindrome(s.substring(1, s.length() - 1)); } // In main: System.out.println(isPalindrome("racecar"));

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

Searching & Sorting (Questions 37-50)

Question 37

What is the time complexity of binary search?

A) O(1)
B) O(n)
C) O(log n)
D) O(n²)

Question 38

What requirement must be met to use binary search?

A) Array must contain integers
B) Array must be sorted
C) Array must have unique elements
D) Array must have even length

Question 39

What is printed?

int[] arr = {2, 4, 6, 8, 10, 12, 14, 16}; int target = 10; int low = 0, high = arr.length - 1; int steps = 0; while (low <= high) { steps++; int mid = (low + high) / 2; if (arr[mid] == target) break; else if (arr[mid] < target) low = mid + 1; else high = mid - 1; } System.out.println(steps);

A) 1
B) 2
C) 3
D) 4

Question 40

What is the time complexity of selection sort?

A) O(n)
B) O(n log n)
C) O(n²)
D) O(log n)

Question 41

What sorting algorithm does this code implement?

for (int i = 0; i < arr.length - 1; i++) { int minIdx = i; for (int j = i + 1; j < arr.length; j++) { if (arr[j] < arr[minIdx]) { minIdx = j; } } // swap arr[i] and arr[minIdx] }

A) Bubble sort
B) Insertion sort
C) Selection sort
D) Merge sort

Question 42

What sorting algorithm does this code implement?

for (int i = 1; i < arr.length; i++) { int key = arr[i]; int j = i - 1; while (j >= 0 && arr[j] > key) { arr[j + 1] = arr[j]; j--; } arr[j + 1] = key; }

A) Bubble sort
B) Insertion sort
C) Selection sort
D) Quick sort

Question 43

After one pass of selection sort on {5, 2, 8, 1, 9}, what is the array?

A) {1, 2, 8, 5, 9}
B) {2, 5, 8, 1, 9}
C) {1, 5, 8, 2, 9}
D) {5, 2, 1, 8, 9}

Question 44

After one pass of insertion sort on {5, 2, 8, 1, 9}, what is the array?

A) {1, 2, 5, 8, 9}
B) {2, 5, 8, 1, 9}
C) {5, 2, 8, 1, 9}
D) {2, 5, 1, 8, 9}

Question 45

What is the time complexity of merge sort?

A) O(n)
B) O(n log n)
C) O(n²)
D) O(log n)

Question 46

Which search is better for a small unsorted array?

A) Binary search
B) Linear search
C) Both are equally good
D) Neither works

Question 47

How many comparisons does linear search need in the worst case for an array of 100 elements?

A) 7
B) 50
C) 100
D) 10

Question 48

How many comparisons does binary search need in the worst case for an array of 100 elements?

A) 7
B) 50
C) 100
D) 10

Question 49

What is returned when binary search doesn't find the target?

public static int binarySearch(int[] arr, int target) { int low = 0, high = arr.length - 1; while (low <= high) { int mid = (low + high) / 2; if (arr[mid] == target) return mid; else if (arr[mid] < target) low = mid + 1; else high = mid - 1; } return -1; }

A) 0
B) -1
C) null
D) throws exception

Question 50

Which statement about sorting is FALSE?

A) Selection sort always makes n-1 swaps
B) Insertion sort is efficient on nearly sorted arrays
C) Merge sort requires O(n) extra space
D) Selection sort is faster than merge sort

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