Mostly Asked Cognizant Interview Questions and Answers

What to Expect in Cognizant Interviews?

Cognizant’s interview process typically involves the following stages:

• Online Aptitude Test: Covers logical reasoning, quantitative ability, and verbal ability.
• Technical Round: Tests your knowledge of programming languages, algorithms, and technical problem-solving.
• HR Round: Assess your personality, communication skills, and alignment with Cognizant's values.

Understanding Cognizant Interview Process

Cognizant Interview Questions For Freshers

Here are some commonly asked interview questions for freshers at Cognizant, along with sample answers to help you prepare effectively:

1. Explain the Four Pillars of Object-Oriented Programming (OOP).

Answer: The four pillars of OOP are:

• Encapsulation: Binding data and methods that operate on that data into a single unit (class).
• Inheritance: Allowing a class to inherit properties and methods from another class.
• Polymorphism: Enabling methods to perform different actions based on the object that invokes them.
• Abstraction: Hiding implementation details and showing only the essential features of an object.

2. What is the difference between a stack and a queue?

Answer:

• Stack: Operates on a LIFO (Last In, First Out) principle. Example: Backtracking in recursion.
• Queue: Operates on a FIFO (First In, First Out) principle. Example: Task scheduling in operating systems.

3. Write a program to check if a number is prime.

Answer:

def is_prime(num):
        if num <= 1:
            return False
        for i in range(2, int(num ** 0.5) + 1):
            if num % i == 0:
                return False
        return True

    # Example Usage
    print(is_prime(7))  # Output: True 

4. What is the difference between primary and foreign keys in SQL?

Answer: Let's see the main difference between the Primary Key and the Foreign Key:

• Primary Key: A unique identifier for each row in a table. It cannot have NULL values.
• Foreign Key: A field in one table that uniquely identifies a row in another table, establishing a relationship between the tables.

5. Explain the concept of normalization in databases.

Answer: Normalization organizes data to reduce redundancy and dependency.

• 1NF: Eliminate duplicate columns and create separate tables for related data.
• 2NF: Remove subsets of data that apply to multiple rows.
• 3NF: Eliminate columns not dependent on the primary key.

6. How would you explain the Agile methodology?

Answer: Agile is an iterative and incremental approach to software development. It emphasizes collaboration, customer feedback, and small, rapid releases to ensure continuous improvement.

7. What is the difference between HTTP and HTTPS?

Answer:

• HTTP: Unencrypted communication protocol.
• HTTPS: Secure version of HTTP that uses SSL/TLS encryption for data transmission.

8. What are the main types of software testing?

Answer:

• Unit Testing: Testing individual components.
• Integration Testing: Testing interactions between modules.
• System Testing: Testing the complete application.
• Acceptance Testing: Verifying that the system meets business requirements.

9. What is recursion? Provide an example.

Answer: Recursion is a process where a function calls itself to solve smaller instances of a problem. Example:

 def factorial(n):
        if n == 0:
            return 1
        return n * factorial(n - 1)
 print(factorial(5))  # Output: 120

10. How would you explain the difference between compilation and interpretation?

Answer:

• Compilation: Converts the entire program into machine code before execution. Example: C, C++.
• Interpretation: Executes code line-by-line. Example: Python, JavaScript.

Pro Tips for Freshers:

• Brush up on fundamental concepts like data structures, algorithms, and database management.
• Practice coding problems on platforms like HackerRank LeetCode, and Scholarhat.
• Prepare to explain your academic projects and the technologies used.
• Develop concise answers for HR questions like career goals and strengths/weaknesses.

By preparing these questions thoroughly, you’ll be better equipped to excel in Cognizant's interviews. Good luck!

Cognizant Interview Questions For Experienced

11. Can you explain the difference between an abstract class and an interface in Java?

Answer:

• Abstract Class: Can have both abstract and concrete methods. It can maintain state (fields) and provide a default implementation. A class can extend only one abstract class.
• Interface: Only defines method signatures (can have default or static methods since Java 8). It cannot maintain state (fields), and a class can implement multiple interfaces.

12. How do you handle memory management in Java?

Answer: Memory management in Java is handled by the JVM using automatic garbage collection. The JVM manages memory allocation for objects and deallocates memory when objects are no longer in use. Developers can use the System.gc() method to suggest garbage collection, but it’s not guaranteed to run immediately.

13. Explain how multithreading works in Java.

Answer: Multithreading in Java allows concurrent execution of two or more threads, enabling parallelism. Java provides the Thread class and the Runnable interface to implement multithreading. Threads can run concurrently, and synchronization is used to ensure that shared resources are accessed by only one thread at a time to prevent conflicts or data corruption.

14. What is a deadlock in Java? How do you prevent it?

Answer: A deadlock occurs when two or more threads are blocked forever due to circular dependencies on resources. To prevent deadlock, avoid nested locks, use a timeout for lock acquisition, or use higher-level concurrency utilities like ReentrantLock that can avoid deadlock situations.

15. Can you explain the difference between SQL JOIN and UNION?

Answer:

• JOIN: Combines columns from two or more tables based on a related column between them (e.g., primary key and foreign key). It can be of various types: INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
• UNION: Combines results of two or more SELECT statements and returns a single result set. It ensures distinct rows and does not combine columns. The number of columns and data types must be the same in each SELECT.

16. What is the difference between a HashMap and a TreeMap in Java?

Answer:

• HashMap: Hasmap in Java stores key-value pairs and allows null values. It does not guarantee any specific order of elements as it uses a hash table for storage.
• TreeMap: A sorted map that orders its elements based on their natural ordering or by a comparator. It does not allow null keys but allows null values.

17. How do you optimize SQL queries for performance?

Answer: To optimize SQL queries:

• Use indexes on columns that are frequently queried.
• Avoid using SELECT *; instead, specify required columns.
• Use joins instead of subqueries when possible.
• Make use of EXPLAIN to analyze query plans and identify performance bottlenecks.
• Minimize the use of OR clauses and use IN when checking multiple values.

18. Explain the concept of inheritance and how it is implemented in C++.

Answer: Inheritance in C++ is a fundamental concept in object-oriented programming where a class (derived class) inherits properties and behaviors from another class (base class). In C++, inheritance is implemented using the : public keyword (for public inheritance). This allows the derived class to access public and protected members of the base class.

class Base {
  public:
  void display()   {
    cout << "Base class display method." << endl;
   }
   };
   class Derived : public Base {
   public:
  oid show() {
  cout << "Derived class show method." << endl;
   }
  }; 

19. What is polymorphism in OOP, and how do you implement it in C++?

Answer: Polymorphism in C++ is the ability of an object to take on multiple forms. It can be implemented through method overloading and method overriding.

class Animal{
  public:
  virtual void sound() {
  cout << "Animal makes a sound." << endl;
 }
 };
 class Dog : public Animal {
 public:
 void sound() override {
 cout << "Dog barks." << endl;
 }
 };   

20. What is Dependency Injection in Spring?

Answer: Dependency Injection (DI) is a design pattern used in Spring Framework to reduce the dependency between objects. Instead of creating an object directly inside a class, the required dependencies are injected into the class, typically through the constructor, setter methods, or fields. It improves code maintainability and testing.

class Employee {
  private Address address;

  @Autowired
  public Employee(Address address){
  this.address = address;
 }
 }   

21. What is the significance of the final keyword in Java?

Answer: The final keyword in Java is used in various contexts:

• Final variable: It can be initialized only once, making the variable constant.
• Final method: It cannot be overridden by subclasses.
• Final class: It cannot be subclassed.

22. Explain the differences between TCP and UDP.

Answer:

• TCP (Transmission Control Protocol): A connection-oriented protocol that ensures reliable data delivery by establishing a connection before data transfer. It guarantees packet order and retransmission of lost packets.
• UDP (User Datagram Protocol): A connectionless protocol that does not guarantee delivery or order of packets, making it faster but less reliable. Used in applications like video streaming, where speed is more critical than reliability.

Pro Tips for Experienced Candidates:

• Revise advanced technical concepts and focus on system design, databases, and concurrency.
• Practice explaining complex problems and solutions clearly and concisely.
• Be ready to answer scenario-based questions that test problem-solving and troubleshooting skills.
• Prepare for coding tests with a strong focus on algorithm optimization and time complexity.

By preparing well for these questions, you can successfully navigate Cognizant's technical interview process. Good luck!