D&K Technologies Java Developer Interview Questions, Process, and Tips

Q1. Stringbuilder and string buffer diff
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Q2. Where we store the object of string
Ans. 
Objects of String are stored in the String Pool in Java.
• String objects are stored in the String Pool, a special memory area in Java heap memory.

• String literals are automatically stored in the String Pool.

• String objects created using the new keyword are not stored in the String Pool.

• String.intern() method can be used to store a String object in the String Pool.
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Q3. What is bean in springboot
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A bean in Spring Boot is a Java object that is instantiated, assembled, and managed by the Spring IoC container.
• Beans are defined in the Spring configuration file or using annotations like @Component, @Service, @Repository, etc.

• Beans are singleton by default but can be scoped as prototype, request, session, etc.

• Beans are injected into other beans using dependency injection.

• Example: @Component annotation is used to defi
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Q4. What is query parameters and path param
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Query parameters are used to pass data to a web server through the URL, while path parameters are part of the URL itself.
• Query parameters are key-value pairs added to the end of a URL after a '?'

• Path parameters are variables within the URL path itself, denoted by curly braces {}

• Example of query parameter: www.example.com/api/users?id=123

• Example of path parameter: www.example.com/api/users/{userId}
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Q5. Code snippet related to exception
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Q6. Diff between exception and error
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Exceptions are recoverable errors that can be handled in code, while errors are unrecoverable issues that usually result in program termination.
• Exceptions are checked at compile time, while errors are unchecked.

• Exceptions are subclasses of Throwable, while errors are subclasses of Error.

• Examples of exceptions include FileNotFoundException, NullPointerException, while examples of errors include OutOfMemoryError, StackOv
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Q1. Write an API to fetch the id and JSON from the client.
Ans. 
Create an API to fetch id and JSON from the client.
• Create a RESTful API endpoint that accepts requests from the client

• Use a GET request to fetch the id and JSON data from the client

• Implement error handling for invalid requests or missing data
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Q2. Find forth highest salary from List using java 8.
Ans. 
Use Java 8 stream to find the forth highest salary from a List.
• Use stream() method to convert the List to a stream.

• Use distinct() method to remove duplicates.

• Use sorted() method to sort the salaries in ascending order.

• Use skip() method to skip the first three highest salaries.

• Use findFirst() method to get the forth highest salary.
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Q1. Microservice Architecture questions
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Q2. Spring Boot Annotations
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Q1. Salary Expectation
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Q2. Basic HR questions
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Q1. Question were asked on basics of Java and SQL. Eg:- OOPS concepts, Collections
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Q1. Questions were asked specific topics on Java and SQL again. This time it was moderate. Eg:- Exception Handling, Springboot, Subquery, Joins etc
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Q1. This round was normal and HR was explaining the company policies and discussed the package.
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Q1. AWS project related
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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. Stream APIs, Default method, Java 8 features
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Q1. Salary negotiation, why change in job
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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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