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I was interviewed in Dec 2024.
Custom stack with constant time access to minimum element
Use two stacks - one to store elements and another to store minimum values
When pushing an element, compare with top of min stack and push the smaller value
When popping an element, pop from both stacks
Access minimum element in O(1) time by peeking at top of min stack
To create an immutable class named Employee with fields for name and hobbies defined as List<String>, use private final fields and return new instances in getters.
Use private final fields for name and hobbies in the Employee class
Provide a constructor to initialize the fields
Return new instances or unmodifiable lists in the getters to ensure immutability
Add hashCode() and equals() methods to Employee class.
Override hashCode() method to generate a unique hash code for each Employee object.
Override equals() method to compare Employee objects based on their attributes.
Ensure that the attributes used in hashCode() and equals() methods are immutable.
Example: Add id, name, and department attributes to Employee class and override hashCode() and equals() methods based on thes
Singleton design pattern ensures a class has only one instance and provides a global point of access to it.
Create a private static instance of the class within the class itself.
Provide a public static method to access the instance, creating it if necessary.
Ensure the constructor of the class is private to prevent instantiation from outside the class.
Use lazy initialization to create the instance only when needed.
Thread...
Ways to create a thread in Java include extending the Thread class, implementing the Runnable interface, and using Java 8's lambda expressions.
Extend the Thread class and override the run() method
Implement the Runnable interface and pass it to a Thread object
Use Java 8's lambda expressions with the Executor framework
SOLID principles are a set of five design principles in object-oriented programming to make software more maintainable, flexible, and scalable.
Single Responsibility Principle (SRP) - A class should have only one reason to change. Example: A class that handles user authentication should not also handle database operations.
Open/Closed Principle (OCP) - Software entities should be open for extension but closed for modific...
OOP is a programming paradigm based on the concept of objects, which can contain data in the form of fields and code in the form of procedures.
OOP focuses on creating objects that interact with each other to solve a problem.
Encapsulation is a key concept in OOP, where data is kept within an object and only accessible through its methods.
Inheritance allows objects to inherit attributes and methods from parent classes.
Po...
Threads communicate in Java through shared memory or message passing.
Threads can communicate through shared variables in memory.
Threads can communicate through synchronized methods or blocks.
Threads can communicate through wait(), notify(), and notifyAll() methods.
Threads can communicate through message passing using classes like BlockingQueue or ExecutorService.
Program to reverse a linked list
Create a new linked list to store the reversed elements
Traverse the original linked list and insert each node at the beginning of the new list
Update the head of the new list as the last node of the original list
String literals are constant strings defined in code, while the string pool is a memory area where unique string objects are stored.
String literals are created using double quotes, while string pool objects are created using the 'new' keyword.
String literals are stored in the string pool to conserve memory and improve performance.
String literals are automatically interned by the JVM, while string pool objects need to b
Program to print the 90-degree rotated view of a 2D array.
Iterate through each column in reverse order and print the corresponding row elements.
Repeat this process for all columns to get the rotated view of the 2D array.
I applied via Walk-in and was interviewed in Dec 2024. There were 2 interview rounds.
The assessment consists of basic coding and SQL-related questions, including two challenge questions. The total test duration is 1 hour and 30 minutes, featuring a total of 7 questions, with a passing score of 50% out of 120 points.
I applied via Company Website and was interviewed in Nov 2024. There were 2 interview rounds.
There were 3 to 4 questions related to the camera that needed to be solved within the given time.
Hashmap postmortem involves analyzing performance, memory usage, collisions, and resizing.
Analyze performance: Check for time complexity of operations like get, put, and remove.
Memory usage: Evaluate memory footprint and potential memory leaks.
Collisions: Investigate collision resolution strategies like separate chaining or open addressing.
Resizing: Examine load factor and rehashing process for efficient resizing.
Examp...
Locking mechanism in multithreading is used to control access to shared resources by multiple threads.
Locks are used to prevent multiple threads from accessing shared resources simultaneously
Types of locks include synchronized blocks, ReentrantLock, and ReadWriteLock
Locks help prevent race conditions and ensure data consistency in multithreaded applications
Use SQL query to group by department and find employee with highest salary in each department
Write a SQL query to group by department and select max salary for each department
Join the result with employee table to get employee details
Example: SELECT dept, emp_name, MAX(salary) FROM employees GROUP BY dept
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I applied via Referral and was interviewed in Jul 2024. There were 5 interview rounds.
Five MCQs, 2 moderate-level+1 hard level coding,2 SQL queries.
Hard-level 6 Data structure based questions to write the code.
Convert nested array objects to single array of strings.
Iterate through the nested arrays and flatten them into a single array.
Use recursion to handle multiple levels of nesting.
Example: [["a", "b"], ["c", "d"]] -> ["a", "b", "c", "d"]
Reverse a list node with multiple values in Java.
Create a new linked list to store the reversed nodes.
Traverse the original list and add each node to the front of the new list.
Update the head node of the original list to point to the new list.
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Coding test time limit is 60 minutes it is moderate
I applied via Naukri.com and was interviewed in Jun 2024. There was 1 interview round.
I applied via Naukri.com and was interviewed in Jun 2024. There were 2 interview rounds.
Had multiple choice question on java, code snippet, two coding question (easy), one sql query
Use SQL query to find highest salary from each department in Employee database.
Use GROUP BY clause to group results by department.
Use MAX() function to find highest salary in each group.
Join Employee table with Department table to get department information.
Merge two sorted arrays into a single sorted array.
Create a new array with the combined length of the two input arrays
Use two pointers to iterate through the two input arrays and compare elements
Add the smaller element to the new array and move the pointer for that array forward
Repeat until all elements from both arrays are added to the new array
Flatten an array of strings
Use a recursive function to iterate through the array and flatten it
Check if each element is an array, if so, recursively call the function
Concatenate the elements into a single array
I applied via Job Portal
Java coding questions and mcq
The contract between hashCode and equals method is that if two objects are equal according to the equals method, then their hash codes must also be equal.
hashCode and equals method must be consistent - if two objects are equal according to equals method, their hash codes must be equal
If two objects have the same hash code, they may or may not be equal according to equals method
Overriding equals method in a class requir...
Java 8 introduced several new features including lambda expressions, functional interfaces, streams, and default methods in interfaces.
Lambda expressions allow you to pass functions as arguments.
Functional interfaces have a single abstract method and can be used with lambda expressions.
Streams provide a way to work with sequences of elements.
Default methods allow interfaces to have method implementations.
Ways to start a thread in Java
Extending the Thread class and overriding the run() method
Implementing the Runnable interface and passing it to a Thread object
Using a thread pool from the Executors class
The thread will continue running as it is already active
The thread will not be started again if it is already running
Attempting to start a thread that is already running will not have any effect
The thread will continue its execution without any interruption
Join method is used to wait for a thread to finish its execution, while sleep method is used to pause the execution of a thread for a specified amount of time.
Join method is used to wait for a thread to finish its execution before moving on to the next task.
Sleep method is used to pause the execution of a thread for a specified amount of time, allowing other threads to run.
Example: thread1.join() will wait for thread1 ...
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The duration of Wissen Technology Java Developer interview process can vary, but typically it takes about less than 2 weeks to complete.
based on 21 interviews
2 Interview rounds
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