AP Computer Science A Full-length practice exam 1 — Free with Answer Explanations

Question 1

Which of the following best explains the purpose of the this keyword in the following constructor?

public class Point {
    private double x;
    private double y;
    
    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }
}

A.this calls the parent class constructor.B.this.x refers to the instance variable x, distinguishing it from the parameter x.C.this is required whenever assigning values in a constructor.D.this.x = x assigns the instance variable to the parameter.

Question 2

What is the output of the following code?

System.out.println(Math.abs(-7));
System.out.println(Math.pow(2, 3));

A.7\n8B.7\n8.0C.-7\n8.0D.7\n6.0

Question 3

What is the output of the following code?

int[] arr = new int[5];
for (int i = 0; i < arr.length; i++) {
    arr[i] = i * i;
}
System.out.println(arr[3]);

A.6B.9C.12D.16

Question 4

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 5

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 6

What is the base case in the following recursive method?

public static int factorial(int n) {
    if (n == 0) return 1;
    return n * factorial(n - 1);
}

A.return n * factorial(n - 1)B.if (n == 0) return 1C.There is no base case; this method will recurse forever.D.n * factorial(n - 1) where n == 1

Question 7

What is the value of n after the following code executes?

int n = (int)(Math.random() * 6) + 1;

A.A random integer from 0 to 5B.A random integer from 1 to 6C.A random integer from 0 to 6D.A random double from 1.0 to 6.0

Question 8

Which expression is equivalent to !(a && b) according to De Morgan's Law?

A.!a && !bB.!a || !bC.a || bD.!(a) && !(b)

Question 9

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 10

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 11

What is the output of the following code?

boolean a = true;
boolean b = false;
System.out.println(!a || b);
System.out.println(!(a || b));

A.false\nfalseB.true\nfalseC.false\ntrueD.true\ntrue

Question 12

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 13

What is the output of the following code?

int score = 85;
String grade;
if (score >= 90) {
    grade = "A";
} else if (score >= 80) {
    grade = "B";
} else if (score >= 70) {
    grade = "C";
} else {
    grade = "F";
}
System.out.println(grade);

A.AB.BC.CD.F

Question 14

Given the following code snippet:

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

What is printed?

A.4 3B.12 3C.3 4D.3 3

Question 15

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 16

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 17

Which of the following best demonstrates short-circuit evaluation of &&?

String s = null;
if (s != null && s.length() > 0) {
    System.out.println("Non-empty");
} else {
    System.out.println("Null or empty");
}

A.NullPointerException is thrown.B."Null or empty" is printed.C."Non-empty" is printed.D.Compile error: cannot call length() on potentially null reference.

Question 18

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 19

What is the output of the following code?

int[][] t = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
for (int c = 0; c < t[0].length; c++) {
    for (int r = 0; r < t.length; r++) {
        System.out.print(t[r][c] + " ");
    }
}

A.1 2 3 4 5 6 7 8 9B.1 4 7 2 5 8 3 6 9C.3 6 9 2 5 8 1 4 7D.9 8 7 6 5 4 3 2 1

Question 20

What are the values of x and y after the following code executes?

double x = 5 / 2;
double y = 5.0 / 2;

A.x = 2.5, y = 2.5B.x = 2.0, y = 2.5C.x = 2, y = 2D.x = 2.5, y = 2.0

Question 21

What is the output of the following code?

public class Box {
    private int value;
    
    public Box(int v) {
        value = v;
    }
    
    public void doubleValue() {
        value = value * 2;
    }
    
    public int getValue() { return value; }
}

// In main:
Box b1 = new Box(5);
Box b2 = b1;
b2.doubleValue();
System.out.println(b1.getValue());

A.5B.10C.20D.Compile error

Question 22

Given the following class, which statement correctly accesses the name variable from OUTSIDE the class?

public class Person {
    private String name;
    
    public Person(String n) {
        name = n;
    }
    
    public String getName() {
        return name;
    }
}

A.Person p = new Person("Alice"); System.out.println(p.name);B.Person p = new Person("Alice"); System.out.println(p.getName());C.Person p = new Person("Alice"); System.out.println(Person.name);D.Person p = new Person("Alice"); System.out.println(name);

Question 23

What is the output of the following code?

String s = "abcdef";
System.out.println(s.indexOf("cd"));
System.out.println(s.indexOf("xy"));

A.2\n0B.3\n-1C.2\n-1D.2\nnull

Question 24

How many times does the following loop print "hello"?

for (int i = 0; i < 5; i++) {
    System.out.println("hello");
}

A.4B.5C.6D.Infinite loop

Question 25

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 26

What is the output of the following code?

int[] arr = {4, 2, 7, 1, 5};
for (int i = 0; i < arr.length - 1; i++) {
    if (arr[i] > arr[i + 1]) {
        int temp = arr[i];
        arr[i] = arr[i + 1];
        arr[i + 1] = temp;
    }
}
System.out.println(arr[0] + " " + arr[1]);

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

Question 27

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 28

A class declares public String toString(). Which statement is true about this method?

A.It overloads the Object class's toString() because all classes implicitly extend Object.B.It overrides Object's toString() and is called automatically by print methods and string concatenation.C.It must call super.toString() or a compile error occurs.D.It has no effect because Java does not use toString() automatically.

Question 29

What is the output of the following code?

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

A.Go! 1 2 3B.3 2 1 Go!C.1 2 3 Go!D.3 2 1

Question 30

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

Question 31

A method receives a 2D array and should return the largest value in the array. Which implementation is correct?

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

A.It always returns arr[0][0] because max is never updated.B.It fails to compile because enhanced for-loops cannot iterate over a 2D array's rows.C.It correctly returns the maximum value in the entire 2D array.D.It returns the wrong result if all values are negative.

Question 32

Which of the following correctly defines a constructor for a Dog class?

public class Dog {
    private String name;
    // Which option is a valid constructor?
}

A.public void Dog(String n) { name = n; }B.public Dog(String n) { name = n; }C.private Dog(String n) { name = n; }D.public dog(String n) { name = n; }

Question 33

The following code attempts to print the sum of the main diagonal of a 3×3 array:

int[][] m = {{1, 0, 0}, {0, 5, 0}, {0, 0, 9}};
int diag = 0;
for (int i = 0; i < m.length; i++) {
    diag += m[i][i];
}
System.out.println(diag);

What does it print?

A.0B.9C.14D.15

Question 34

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 35

Given the following code:

Animal a = new Dog();
if (a instanceof Dog) {
    System.out.println("Dog");
} else {
    System.out.println("Not Dog");
}

What is printed, assuming Dog extends Animal?

A.Not DogB.Compile error: cannot use instanceof with a parent type variableC.DogD.Runtime exception: ClassCastException

Question 36

What is the output of the following code?

int x = 0;
if (x = 5) {
    System.out.println("hello");
}

A.helloB.Nothing is printed.C.Compile error: incompatible types.D.Runtime exception.

Question 37

What is the output of the following code?

int x = 5;
if (x > 3) {
    System.out.println("A");
} else if (x > 4) {
    System.out.println("B");
} else {
    System.out.println("C");
}

A.AB.BC.A\nBD.C

Question 38

After the following code executes, what is the value of n?

double d = 7.9;
int n = (int) d % 3;

A.1B.2C.0D.Compile error

Question 39

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 40

Consider a 2D array representing a grid where each row may have a different length (a jagged array). Which expression safely gives the number of columns in row i?

A.arr.lengthB.arr[0].lengthC.arr[i].lengthD.arr.length[i]