D&K Technologies Trainee Interview Questions and Answers

Q1. Thread safety of a class
Ans. 
Ensuring that a class can be safely used by multiple threads concurrently.
• Use synchronized keyword to ensure only one thread can access critical sections at a time.

• Avoid mutable shared state to prevent race conditions.

• Consider using thread-safe data structures like ConcurrentHashMap or AtomicInteger.

• Implementing the java.util.concurrent.locks.Lock interface for more fine-grained control over synchronization.
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Q1. 1) How do you achieve concurrency in your current job, and write code for it? 2) Write code for Rest API using Springboot, need to write Entity, Service, Repository, and Controller classes? 3)Volatile keyw...read more
Ans. 
Answers to common Java Developer interview questions
• 1) Concurrency is achieved using multithreading in Java. Use threads, executors, or synchronized blocks. Example: using ExecutorService to run multiple tasks concurrently.

• 2) Rest API in Springboot: Entity class defines database table, Service class contains business logic, Repository class interacts with database, Controller class handles HTTP requests.

• 3) Volatile key...read more
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Q1. Good queries like
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Q2. Sorting from two array,sum if the number equivalent to sequence of number.
Ans. 
Sort and sum numbers from two arrays based on their sequence.
• Sort both arrays in ascending order.

• Iterate through both arrays simultaneously and compare the elements.

• If the elements are equal, add them and move to the next element in both arrays.

• If the element in the first array is smaller, move to the next element in the first array.

• If the element in the second array is smaller, move to the next element in the second a...read more
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The most common cognitive aptitude tests are the CCAT, PI Cognitive Assessment, Wonderlic test, McQuaig Mental Agility Test (MMAT), and Thomas GIA.

Q1. Interested your self : thank you for giving opportunity to introduce myself . I am Dheeraj Jadhav I am from Karnataka my graduation completed in PDA College of Engineering Kalburgi my stream is Electron...read more
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Q2. Tell me about hobbies: my hobbies is playing cricket watching movie and reading book and helping Nature.
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Q3. Tell me about your technical skill: my technical skill is Java HTML and SQL
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Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round with questions on DSA and Java.

Q1. 
Max Element After Update Operations
Given an array A of size N, initialized with all zeros, and another array ARR of M pairs of integers representing operations. Each operation consists of a range where e...read more
Ans. 
Find the maximum element in an array after performing a series of increment operations on specified ranges.
• Initialize an array of size N with all zeros

• Iterate through the operations and increment elements within specified ranges

• Return the maximum element in the array after all operations
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Q2. Can you explain the internal working of a hash map in Java?
Ans. 
HashMap in Java is a data structure that stores key-value pairs and uses hashing to efficiently retrieve values based on keys.
• HashMap internally uses an array of linked lists to store key-value pairs.

• When a key-value pair is added, the key is hashed to find the index in the array where it will be stored.

• If multiple keys hash to the same index, a linked list is used to handle collisions.

• Retrieving a value involves hashi...read more
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Q3. Why do we need to override the equals and hashCode methods in Java?
Ans. 
Overriding equals and hashCode methods in Java is important for proper object comparison and hashing.
• Equals method is used to compare two objects for equality, while hashCode method is used to generate a unique integer value for an object.

• By overriding equals and hashCode methods, we can ensure that objects are compared based on their actual content rather than memory address.

• This is crucial for collections like HashMa...read more
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Round duration - 60 minutes
Round difficulty - Medium

Technical Interview round with questions based around Java.

Q1. How can you print even and odd numbers in increasing order using two threads in Java?
Ans. 
Use two threads to print even and odd numbers in increasing order.
• Create two threads, one for printing even numbers and one for printing odd numbers.

• Use a shared variable to keep track of the current number to be printed.

• Synchronize access to the shared variable to ensure correct ordering of numbers.

• Use a loop in each thread to print the next number and update the shared variable.
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Q2. What is the internal working of a CopyOnWrite ArrayList?
Ans. 
CopyOnWriteArrayList creates a new copy of the underlying array whenever an element is added, modified, or removed.
• CopyOnWriteArrayList is thread-safe and suitable for scenarios where reads are more frequent than writes.

• Adding, modifying, or removing elements in CopyOnWriteArrayList creates a new copy of the underlying array, ensuring thread safety.

• Iterators on CopyOnWriteArrayList operate on the original array and do
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Q3. What are the differences between Synchronized Collection and Concurrent Collection in Java?
Ans. 
Synchronized Collection is thread-safe but may have performance issues, while Concurrent Collection is optimized for concurrent access.
• Synchronized Collection uses synchronized keyword to achieve thread-safety, while Concurrent Collection uses non-blocking algorithms like CAS (Compare and Swap).

• Synchronized Collection locks the entire collection during modification, leading to potential performance bottlenecks, while C...read more
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Round 1 was an online hackerank coding test + technical MCQs.

It consisted of 5 MCQs + 1 SQL problem + 1 DSA problem based on queue + 1 Graph question + 1 java based question to create a REST API.

Q1. Stream APIs, Default method, Java 8 features
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Q1. Salary negotiation, why change in job
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