Code Snippets-based MCQs

Lists & Sets

Table of contents

Easy Level MCQs
Slightly harder MCQs
Tricky MCQs

Easy Level MCQs

What will be the output of the following code snippet?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<String> list = new ArrayList<>();
         list.add("A");
         list.add("B");
         list.add("C");
         System.out.println(list.size());
     }
 }

Answer

What will the following code snippet print?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Integer> set = new HashSet<>();
         set.add(1);
         set.add(2);
         set.add(1);
         System.out.println(set.size());
     }
 }

Answer

What will be the output of the following code snippet?

 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<String> list = new LinkedList<>();
         list.add("A");
         list.add("B");
         list.remove(1);
         System.out.println(list);
     }
 }

Answer

[A]

What will the following code snippet print?

 import java.util.LinkedHashSet;
 public class Example {
     public static void main(String[] args) {
         LinkedHashSet<String> set = new LinkedHashSet<>();
         set.add("A");
         set.add("B");
         set.add("C");
         for (String s : set) {
             System.out.print(s + " ");
         }
     }
 }

Answer

A B C

What will be the output of the following code snippet?

 import java.util.Vector;
 public class Example {
     public static void main(String[] args) {
         Vector<Integer> vector = new Vector<>(2);
         vector.add(1);
         vector.add(2);
         vector.add(3);
         System.out.println(vector.size());
     }
 }

Answer

What will the following code snippet print?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Integer> list = new ArrayList<>();
         list.add(1);
         list.add(2);
         list.add(3);
         for (int num : list) {
             System.out.print(num + " ");
         }
     }
 }

Answer

1 2 3

What will be the output of the following code snippet?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<String> set = new TreeSet<>();
         set.add("Banana");
         set.add("Apple");
         set.add("Mango");
         System.out.println(set.first());
     }
 }

Answer

Apple

What will the following code snippet print?

 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<Integer> list = new LinkedList<>();
         list.add(10);
         list.add(20);
         list.addFirst(5);
         System.out.println(list.get(0));
     }
 }

Answer

What will be the output of the following code snippet?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<String> set = new HashSet<>();
         set.add("X");
         set.add("Y");
         set.add("Z");
         set.remove("Y");
         System.out.println(set.contains("Y"));
     }
 }

Answer

false

What will the following code snippet print?

import java.util.Vector;
public class Example {
    public static void main(String[] args) {
        Vector<Integer> vector = new Vector<>();
        vector.add(1);
        vector.add(2);
        vector.set(1, 3);
        System.out.println(vector.get(1));
    }
}

Answer

What will happen when the following code snippet is executed?
```
 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<int> list = new ArrayList<>();
         list.add(1);
         list.add(2);
         System.out.println(list.size());
     }
 }
```
Prints 2
Prints 0
Compilation error
Runtime error

Answer

Compilation error

Explanation: In Java, generic types cannot be primitive types like int. Instead, you should use the wrapper class Integer. The correct declaration would be ArrayList<Integer> list = new ArrayList<>();.

What will be the output when the following code snippet is executed?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<String> set = new HashSet<>();
         set.add("A");
         set.add("B");
         set.add("C");
         for (int i = 0; i < set.size(); i++) {
             System.out.print(set.get(i) + " ");
         }
     }
 }

Answer

Compilation error

Explanation: The HashSet class does not have a get(int index) method. Sets in Java do not support indexed access because they are unordered collections. To iterate over a set, you should use an iterator or a for-each loop.

What will happen when the following code snippet is executed?
```
 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<String> list = new LinkedList<>();
         list.add("Hello");
         list.add("World");
         list.add(2, "!");
         System.out.println(list);
     }
 }
```
[Hello, World, !]
[Hello, !, World]
[!, Hello, World]
Runtime error

Answer

[Hello, World, !]

Explanation: The add(int index, E element) method inserts the specified element at the specified position. Since the list initially has two elements at indices 0 and 1, adding an element at index 2 appends it to the end. Therefore, the list becomes [Hello, World, !].

What will be the result of executing the following code snippet?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<Integer> set = new TreeSet<>();
         set.add(null);
         set.add(1);
         set.add(2);
         System.out.println(set);
     }
 }

Answer

Runtime error

Explanation: Adding null to a TreeSet will throw a NullPointerException at runtime because TreeSet requires elements to be comparable for sorting, and null cannot be compared.

What will happen when the following code snippet is executed?

 import java.util.Vector;
 public class Example {
     public static void main(String[] args) {
         Vector<String> vector = new Vector<>(-1);
         vector.add("A");
         vector.add("B");
         System.out.println(vector.size());
     }
 }

Answer

Runtime error

Explanation: Initializing a Vector with a negative initial capacity will throw an IllegalArgumentException at runtime.

What will be the output when the following code snippet is executed?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<String> list = new ArrayList<>();
         list.add("One");
         list.add("Two");
         list.add("Three");
         for (String s : list) {
             if (s.equals("Two")) {
                 list.remove(s);
             }
         }
         System.out.println(list);
     }
 }

Answer

Runtime error

Explanation: Removing elements from a list while iterating over it using a for-each loop will throw a ConcurrentModificationException at runtime. To safely remove elements, use an iterator’s remove() method.

What will happen when the following code snippet is executed?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Integer> set = new HashSet<>();
         set.add(1);
         set.add(2);
         set.add(3);
         for (Integer num : set) {
             if (num == 2) {
                 set.add(4);
             }
         }
         System.out.println(set.size());
     }
 }

Answer

Runtime error

Explanation: Modifying a HashSet while iterating over it will throw a ConcurrentModificationException at runtime.

What will be the output when the following code snippet is executed?

 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<String> list = new LinkedList<>();
         list.add("A");
         list.add("B");
         list.add("C");
         System.out.println(list.get(3));
     }
 }

Answer

Runtime error

Explanation: The get(int index) method will throw an IndexOutOfBoundsException if the index is out of range. Since the list has elements at indices 0, 1, and 2, trying to access index 3 will cause a runtime error.

What will happen when the following code snippet is executed?
```
 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<String> set = new TreeSet<>();
         set.add("Apple");
         set.add("apple");
         set.add("Banana");
         System.out.println(set);
     }
 }
```
[Apple, Banana, apple]
[Apple, apple, Banana]
[Banana, Apple, apple]
[Apple, Banana]

Answer

[Apple, Banana, apple]

Explanation: TreeSet sorts elements according to their natural ordering. In Java, uppercase letters come before lowercase letters in Unicode, so “Apple” < “Banana” < “apple”. Therefore, the set will be ordered as [Apple, Banana, apple].

What will be the output when the following code snippet is executed?

import java.util.Vector;
public class Example {
    public static void main(String[] args) {
        Vector vector = new Vector();
        vector.add("1");
        vector.add(2);
        for (Object obj : vector) {
            System.out.print((String) obj + " ");
        }
    }
}

Answer

Runtime error

Explanation: The code attempts to cast an Integer object (2) to a String, which will throw a ClassCastException at runtime. To avoid this, ensure that all elements are of the same type or handle casting appropriately.

Slightly harder MCQs

What will be the output of the following code snippet?

 import java.util.HashSet;
 import java.util.Iterator;
 public class Example {
     public static void main(String[] args) {
         HashSet<Integer> set = new HashSet<>();
         set.add(10);
         set.add(20);
         set.add(30);
         Iterator<Integer> it = set.iterator();
         while (it.hasNext()) {
             Integer value = it.next();
             if (value % 20 == 0) {
                 it.remove();
             }
         }
         System.out.println(set);
     }
 }

Answer

[10, 30]

Explanation: The code removes elements divisible by 20 using an iterator’s remove() method. Since 20 is divisible by 20, it is removed, leaving [10, 30] in the set.

What will be the output of the following code snippet?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Integer> list = new ArrayList<>();
         list.add(10);
         list.add(20);
         list.add(30);
         for (int i = 0; i < list.size(); i++) {
             list.set(i, list.get(i) + 10);
         }
         System.out.println(list);
     }
 }

Answer

[20, 30, 40]

Explanation: The code iterates through the list and increases each element by 10 using the set method. The final list is [20, 30, 40].

What will happen when the following code snippet is executed?

 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<String> list = new LinkedList<>();
         list.add("A");
         list.add("B");
         list.add("C");
         list.removeFirst();
         list.addFirst("D");
         System.out.println(list);
     }
 }

Answer

[D, B, C]

Explanation: The code first removes the first element “A” from the list, and then adds “D” to the beginning. The final list is [D, B, C].

What will happen when the following code snippet is executed?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<Integer> set = new TreeSet<>();
         set.add(10);
         set.add(5);
         set.add(20);
         set.add(5);
         System.out.println(set);
     }
 }

Answer

[5, 10, 20]

Explanation: TreeSet maintains a sorted order and does not allow duplicate elements. The final set is [5, 10, 20].

What will be the result of executing the following code snippet?

 import java.util.Vector;
 public class Example {
     public static void main(String[] args) {
         Vector<String> vector = new Vector<>();
         vector.add("A");
         vector.add("B");
         vector.add("C");
         vector.add(1, "D");
         vector.remove("C");
         System.out.println(vector);
     }
 }

Answer

[A, D, B]

Explanation: The code inserts “D” at index 1, shifting the elements to the right, and then removes “C”. The final vector is [A, D, B].

What will be the output when the following code snippet is executed?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Integer> set = new HashSet<>();
         set.add(1);
         set.add(2);
         set.add(3);
         set.add(2);
         System.out.println(set.size());
     }
 }

Answer

Explanation: HashSet does not allow duplicate elements, so adding “2” twice has no effect. The set contains 3 unique elements: 1, 2, and 3.

What will happen when the following code snippet is executed?

 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<Integer> list = new LinkedList<>();
         list.add(1);
         list.add(2);
         list.add(3);
         list.addLast(4);
         list.removeFirst();
         System.out.println(list);
     }
 }

Answer

[2, 3, 4]

Explanation: The code adds 4 to the end of the list and then removes the first element, resulting in the list [2, 3, 4].

What will happen when the following code snippet is executed?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<String> set = new TreeSet<>();
         set.add("Banana");
         set.add("Apple");
         set.add("Mango");
         System.out.println(set);
     }
 }

Answer

[Apple, Banana, Mango]

Explanation: TreeSet stores elements in a natural sorted order. The final set is [Apple, Banana, Mango].

What will be the output when the following code is executed?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Integer> list = new ArrayList<>();
         list.add(1);
         list.add(2);
         list.add(3);
         list.add(0, 0);
         list.remove(2);
         System.out.println(list);
     }
 }

Answer

[0, 1, 3]

Explanation: The code inserts 0 at the beginning of the list, and then removes the element at index 2 (which is 2), resulting in [0, 1, 3].

What will be the output when the following code snippet is executed?

import java.util.HashSet;
public class Example {
    public static void main(String[] args) {
        HashSet<String> set = new HashSet<>();
        set.add("apple");
        set.add("banana");
        set.add("cherry");
        set.add("banana");
        System.out.println(set.contains("banana"));
    }
}

Answer

true

Explanation: HashSet allows only unique elements, and the contains method checks if an element exists in the set. Since “banana” is in the set, the output is true.

Given a Student class with a constructor that initializes the name and age fields, what will be the output of the following code snippet?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Student> students = new ArrayList<>();
         students.add(new Student("Alice", 20));
         students.add(new Student("Bob", 22));
         students.add(new Student("Charlie", 21));
         System.out.println(students.size());
     }
 }

Answer

Explanation: The code adds three Student objects to the ArrayList, so the size of the list is 3.

Given a Student class with a name field and a method getName() that returns the student’s name, what will be the output of the following code snippet?

 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<Student> students = new LinkedList<>();
         students.add(new Student("Alice"));
         students.add(new Student("Bob"));
         students.addFirst(new Student("Eve"));
         System.out.println(students.getFirst().getName());
     }
 }

Answer

Eve

Explanation: addFirst inserts the student “Eve” at the beginning of the list, so getFirst().getName() returns “Eve”.

Given a Student class with fields name and age, what will be the output of the following code snippet?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Student> students = new HashSet<>();
         students.add(new Student("Alice", 20));
         students.add(new Student("Bob", 22));
         students.add(new Student("Alice", 20));
         System.out.println(students.size());
     }
 }

Answer

Explanation: If the Student class does not override equals and hashCode, the two Student objects with the same data are treated as different objects. So, the size of the set is 2.

Given a Student class with fields name and age, what will be the output of the following code snippet?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<Student> students = new TreeSet<>();
         students.add(new Student("Alice", 20));
         students.add(new Student("Bob", 22));
         students.add(new Student("Charlie", 21));
         System.out.println(students);
     }
 }

Answer

Compilation error

Explanation: TreeSet requires elements to be comparable, so the Student class must implement Comparable or provide a Comparator when creating the TreeSet.

Given a Student class with fields name and age, what will be the output of the following code snippet?

 import java.util.Vector;
 public class Example {
     public static void main(String[] args) {
         Vector<Student> students = new Vector<>();
         students.add(new Student("Alice", 20));
         students.add(new Student("Bob", 22));
         students.add(new Student("Charlie", 21));
         students.remove(1);
         System.out.println(students.size());
     }
 }

Answer

Explanation: The code removes the student at index 1, so the size of the Vector becomes 2.

Given a Student class with fields name and grade, what will be the output of the following code snippet?

 import java.util.LinkedHashSet;
 public class Example {
     public static void main(String[] args) {
         LinkedHashSet<Student> students = new LinkedHashSet<>();
         students.add(new Student("Alice", "A"));
         students.add(new Student("Bob", "B"));
         students.add(new Student("Charlie", "C"));
         for (Student student : students) {
             System.out.print(student.getName() + " ");
         }
     }
 }

Answer

Alice Bob Charlie

Explanation: LinkedHashSet maintains the insertion order, so the elements are printed in the order they were added.

Given a Student class with fields name and grade, what will be the output of the following code snippet?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Student> students = new ArrayList<>();
         students.add(new Student("Alice", "A"));
         students.add(new Student("Bob", "B"));
         students.add(new Student("Charlie", "C"));
         students.clear();
         System.out.println(students.isEmpty());
     }
 }

Answer

true

Explanation: The clear() method removes all elements from the list, making it empty. The isEmpty() method returns true.

Given a Student class with fields name and marks, what will be the output of the following code snippet?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Student> students = new HashSet<>();
         students.add(new Student("Alice", 85));
         students.add(new Student("Bob", 92));
         students.add(new Student("Charlie", 78));
         for (Student student : students) {
             if (student.getMarks() > 80) {
                 System.out.print(student.getName() + " ");
             }
         }
     }
 }

Answer

Alice Bob

Explanation: The code prints the names of students with marks greater than 80, so “Alice” and “Bob” are printed.

Given a Student class with fields name and marks, what will be the output of the following code snippet?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<Student> students = new TreeSet<>(new Comparator<Student>() {
             public int compare(Student s1, Student s2) {
                 return s2.getMarks() - s1.getMarks();
             }
         });
         students.add(new Student("Alice", 85));
         students.add(new Student("Bob", 92));
         students.add(new Student("Charlie", 78));
         System.out.println(students.first().getName());
     }
 }

Answer

Bob

Explanation: The custom comparator sorts students by marks in descending order, so first() returns “Bob”, who has the highest marks.

Given a Student class with fields name and marks, what will be the output of the following code snippet?

import java.util.Vector;
public class Example {
    public static void main(String[] args) {
        Vector<Student> students = new Vector<>();
        students.add(new Student("Alice", 85));
        students.add(new Student("Bob", 92));
        students.add(new Student("Charlie", 78));
        students.remove(new Student("Alice", 85));
        System.out.println(students.size());
    }
}

Answer

Explanation: If the Student class does not override equals and hashCode, the remove method won’t find a match, and the size remains unchanged at 3. If it does, the size will be 2.

Given a Book class with fields title and author, what will be the output of the following code snippet?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Book> books = new ArrayList<>();
         books.add(new Book("1984", "George Orwell"));
         books.add(new Book("Brave New World", "Aldous Huxley"));
         books.add(new Book("Fahrenheit 451", "Ray Bradbury"));
         System.out.println(books.size());
     }
 }

Answer

Explanation: The code adds three Book objects to the ArrayList, so the size of the list is 3.

Given a Movie class with fields title and year, what will be the output of the following code snippet?

 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<Movie> movies = new LinkedList<>();
         movies.add(new Movie("Inception", 2010));
         movies.add(new Movie("The Matrix", 1999));
         movies.addFirst(new Movie("Interstellar", 2014));
         System.out.println(movies.getFirst().getTitle());
     }
 }

Answer

Interstellar

Explanation: addFirst inserts the movie “Interstellar” at the beginning of the list, so getFirst().getTitle() returns “Interstellar”.

Given a Person class with fields name and age, what will be the output of the following code snippet?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Person> people = new HashSet<>();
         people.add(new Person("Alice", 30));
         people.add(new Person("Bob", 25));
         people.add(new Person("Alice", 30));
         System.out.println(people.size());
     }
 }

Answer

Explanation: If the Person class does not override equals and hashCode, the two Person objects with the same data are treated as different objects. So, the size of the set is 2.

Given a Song class with fields title and artist, what will be the output of the following code snippet?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<Song> playlist = new TreeSet<>();
         playlist.add(new Song("Bohemian Rhapsody", "Queen"));
         playlist.add(new Song("Stairway to Heaven", "Led Zeppelin"));
         playlist.add(new Song("Hotel California", "Eagles"));
         System.out.println(playlist);
     }
 }

Answer

Compilation error

Explanation: TreeSet requires elements to be comparable, so the Song class must implement Comparable or provide a Comparator when creating the TreeSet.

Given a Product class with fields name and price, what will be the output of the following code snippet?

 import java.util.Vector;
 public class Example {
     public static void main(String[] args) {
         Vector<Product> products = new Vector<>();
         products.add(new Product("Laptop", 1000));
         products.add(new Product("Smartphone", 700));
         products.add(new Product("Tablet", 500));
         products.remove(1);
         System.out.println(products.size());
     }
 }

Answer

Explanation: The code removes the product at index 1, so the size of the Vector becomes 2.

Given a City class with fields name and population, what will be the output of the following code snippet?

 import java.util.LinkedHashSet;
 public class Example {
     public static void main(String[] args) {
         LinkedHashSet<City> cities = new LinkedHashSet<>();
         cities.add(new City("New York", 8419000));
         cities.add(new City("Los Angeles", 3980000));
         cities.add(new City("Chicago", 2716000));
         for (City city : cities) {
             System.out.print(city.getName() + " ");
         }
     }
 }

Answer

New York Los Angeles Chicago

Explanation: LinkedHashSet maintains the insertion order, so the elements are printed in the order they were added.

Given an Animal class with fields species and age, what will be the output of the following code snippet?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Animal> zoo = new ArrayList<>();
         zoo.add(new Animal("Elephant", 10));
         zoo.add(new Animal("Tiger", 5));
         zoo.add(new Animal("Giraffe", 7));
         zoo.clear();
         System.out.println(zoo.isEmpty());
     }
 }

Answer

true

Explanation: The clear() method removes all elements from the list, making it empty. The isEmpty() method returns true.

Given a Car class with fields make and year, what will be the output of the following code snippet?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Car> garage = new HashSet<>();
         garage.add(new Car("Toyota", 2018));
         garage.add(new Car("Honda", 2020));
         garage.add(new Car("Ford", 2019));
         for (Car car : garage) {
             if (car.getYear() > 2018) {
                 System.out.print(car.getMake() + " ");
             }
         }
     }
 }

Answer

Honda Ford

Explanation: The loop checks if the car’s year is greater than 2018, so “Honda” and “Ford” are printed since they were manufactured after 2018.

Given a Gadget class with fields name and price, what will be the output of the following code snippet?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<Gadget> gadgets = new TreeSet<>(new Comparator<Gadget>() {
             public int compare(Gadget g1, Gadget g2) {
                 return g1.getPrice() - g2.getPrice();
             }
         });
         gadgets.add(new Gadget("Smartphone", 700));
         gadgets.add(new Gadget("Tablet", 500));
         gadgets.add(new Gadget("Laptop", 1000));
         System.out.println(gadgets.last().getName());
     }
 }

Answer

Laptop

Explanation: The custom comparator sorts the gadgets by price in ascending order, so the last element (highest price) is “Laptop”.

Given a Course class with fields courseName and duration, what will be the output of the following code snippet?

import java.util.LinkedList;
public class Example {
    public static void main(String[] args) {
        LinkedList<Course> courses = new LinkedList<>();
        courses.add(new Course("Java", 30));
        courses.add(new Course("Python", 25));
        courses.add(new Course("JavaScript", 20));
        courses.removeLast();
        System.out.println(courses.getLast().getCourseName());
    }
}

Answer

Python

Explanation: The removeLast() method removes the last course in the list, leaving “Java” and “Python”. The getLast() method then returns the course name of the last remaining course, “Python”.

Tricky MCQs

Given a Developer class with fields name and experience, and assuming equals and hashCode are correctly overridden, what will be the output of the following code snippet?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Developer> team = new HashSet<>();
         Developer dev1 = new Developer("Alice", 5);
         Developer dev2 = new Developer("Bob", 3);
         team.add(dev1);
         team.add(dev2);
         dev1.setExperience(6);
         System.out.println(team.contains(new Developer("Alice", 6)));
     }
 }

Answer

false

Explanation: Modifying an object in a HashSet after it’s been added can lead to unexpected behavior, as the object’s hash code might change, making it difficult to find the object.

Given an Employee class with fields id and department, and assuming equals and hashCode are correctly overridden, what will be the output of the following code snippet?

 import java.util.LinkedHashSet;
 public class Example {
     public static void main(String[] args) {
         LinkedHashSet<Employee> employees = new LinkedHashSet<>();
         employees.add(new Employee(1, "HR"));
         employees.add(new Employee(2, "Finance"));
         employees.add(new Employee(1, "HR"));
         employees.add(new Employee(3, "Engineering"));
         System.out.println(employees.size());
     }
 }

Answer

Explanation: Since equals and hashCode are overridden, duplicates based on the same id and department are not added. So the size is 3.

Given a Course class with fields title and duration, and assuming Course implements Comparable<Course> based on title, what will be the output of the following code snippet?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<Course> courses = new TreeSet<>();
         courses.add(new Course("Math", 40));
         courses.add(new Course("Science", 35));
         courses.add(new Course("Math", 30));
         System.out.println(courses.size());
     }
 }

Answer

Explanation: Since Course objects are compared based on title, “Math” is considered a duplicate, and only two unique courses (“Math” and “Science”) are added.

Given a Building class with fields name and height, what will be the output of the following code snippet?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Building> buildings = new ArrayList<>();
         buildings.add(new Building("Empire State", 1250));
         buildings.add(new Building("Burj Khalifa", 2717));
         buildings.remove(new Building("Empire State", 1250));
         System.out.println(buildings.size());
     }
 }

Answer

Explanation: Without overriding equals and hashCode, remove does not find the object in the list, so the size remains 2.

Given a Gadget class with fields model and price, and assuming equals and hashCode are correctly overridden, what will be the output of the following code snippet?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Gadget> gadgets = new HashSet<>();
         gadgets.add(new Gadget("iPhone", 999));
         gadgets.add(new Gadget("iPhone", 999));
         gadgets.add(new Gadget("Samsung", 899));
         gadgets.add(new Gadget("iPhone", 1099));
         System.out.println(gadgets.size());
     }
 }

Answer

Explanation: The first two “iPhone” gadgets are considered duplicates and are not added again, but the third “iPhone” with a different price is added.

Given a Team class with fields name and rank, what will be the output of the following code snippet?

 import java.util.LinkedList;
 public class Example {
     public static void main(String[] args) {
         LinkedList<Team> teams = new LinkedList<>();
         teams.add(new Team("Alpha", 1));
         teams.add(new Team("Beta", 2));
         teams.add(new Team("Gamma", 3));
         teams.add(1, new Team("Delta", 4));
         System.out.println(teams.get(1).getName());
     }
 }

Answer

Delta

Explanation: The add(1, new Team("Delta", 4)) inserts “Delta” at index 1, pushing the other elements to the right.

Given a Library class with fields name and booksCount, and assuming Library implements Comparable<Library> based on booksCount, what will be the output of the following code snippet?

 import java.util.TreeSet;
 public class Example {
     public static void main(String[] args) {
         TreeSet<Library> libraries = new TreeSet<>();
         libraries.add(new Library("Central", 10000));
         libraries.add(new Library("East", 8000));
         libraries.add(new Library("West", 12000));
         libraries.add(new Library("Central", 10000));
         System.out.println(libraries.first().getName());
     }
 }

Answer

East

Explanation: The TreeSet orders libraries by booksCount, and the one with the smallest booksCount is “East”.

Given a Student class with fields name and grade, and assuming equals and hashCode are correctly overridden, what will be the output of the following code snippet?

 import java.util.HashSet;
 public class Example {
     public static void main(String[] args) {
         HashSet<Student> students = new HashSet<>();
         Student s1 = new Student

 ("John", "A");
         Student s2 = new Student("Jane", "B");
         students.add(s1);
         students.add(s2);
         s1.setGrade("B");
         System.out.println(students.contains(new Student("John", "B")));
     }
 }

Answer

false

Explanation: Changing s1’s grade after adding it to the set affects its hash code, making it difficult to find in the set, so contains returns false.

Given a Country class with fields name and population, and assuming equals and hashCode are correctly overridden, what will be the output of the following code snippet?

 import java.util.ArrayList;
 public class Example {
     public static void main(String[] args) {
         ArrayList<Country> countries = new ArrayList<>();
         countries.add(new Country("USA", 331000000));
         countries.add(new Country("India", 1391000000));
         countries.add(new Country("China", 1440000000));
         countries.add(1, new Country("Russia", 146000000));
         countries.remove(0);
         System.out.println(countries.get(1).getName());
     }
 }

Answer

India

Explanation: “Russia” is added at index 1, pushing “India” to index 2. Removing index 0 removes “USA”, so “India” moves back to index 1.

Given a Product class with fields name and price, and assuming Product implements Comparable<Product> based on price, what will be the output of the following code snippet?

import java.util.TreeSet;
public class Example {
    public static void main(String[] args) {
        TreeSet<Product> products = new TreeSet<>();
        products.add(new Product("Phone", 700));
        products.add(new Product("Tablet", 500));
        products.add(new Product("Laptop", 1200));
        System.out.println(products.pollFirst().getName());
    }
}

Answer

Tablet

Explanation: The TreeSet orders products by price, and pollFirst() retrieves and removes the lowest-priced product, which is “Tablet”.