Cognizant Java Developer Interview Questions, Process, and Tips

Simple aptitude test

Coding questions based on data structures

Q1. Two coding questions based on algorithms
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Q2. Palindrome substrings, it is a dynamic problem
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Q3. Permutations, it is a Backtracking problem
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Q1. Internal working of hashmap?
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HashMap is a data structure that stores key-value pairs and uses hashing to retrieve values.
• HashMap uses an array of buckets to store key-value pairs

• Each bucket contains a linked list of entries

• Hashing is used to determine the index of the bucket where the entry should be stored

• If multiple entries have the same hash code, they are stored in the same bucket as a linked list

• HashMap allows null keys and values

• HashMap is n...read more
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Q2. How to create immutable classes?
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Immutable classes cannot be modified after creation. They ensure thread safety and prevent bugs.
• Make the class final so it cannot be extended

• Make all fields private and final

• Do not provide any setters, only getters

• If a field is mutable, return a copy of it in the getter

• Consider using a builder pattern for complex objects
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Q3. How to create singleton class ?
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Singleton class is a class that can only have one instance at a time.
• Create a private constructor to prevent instantiation from outside the class.

• Create a private static instance of the class.

• Create a public static method to get the instance of the class.

• Ensure thread safety by using synchronized keyword or static initializer.

• Example: public class Singleton { private static Singleton instance = null; private Singleton(...read more
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Q4. We have a employee class having empId, name and salary fields. I have around 1000 employee objects, I want to sort them according employee name is descending order?
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Q5. Basic OOPS related questions?
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Q6. Difference between List and Set? which one to prefer in which requirements and why ?
Ans. 
List allows duplicates and maintains insertion order, Set doesn't allow duplicates and doesn't maintain order.
• Use List when duplicates are allowed and order is important

• Use Set when duplicates are not allowed and order is not important

• List examples: ArrayList, LinkedList

• Set examples: HashSet, TreeSet
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Q7. Spring Boot basic questions?
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Q8. How to implement Spring security with JWT token?
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Implementing Spring security with JWT token involves configuring security filters and authentication providers.
• Add dependencies for Spring Security and JWT

• Configure security filters to validate JWT tokens

• Implement authentication provider to authenticate users

• Generate and sign JWT tokens for successful authentication

• Example: https://www.baeldung.com/spring-security-jwt
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Q1. Current project, spring related questions
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Q1. Core java interview questions
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