Wissen Technology Software Engineer Interview Questions and Answers

2 coding questions and some MCQs on Java and SQL.

Q1. How to use custom object as a key in HashMap?
Ans. 
To use a custom object as a key in HashMap, override hashCode() and equals() methods in the custom object class.
• Override hashCode() method to generate a unique hash code for the custom object.

• Override equals() method to compare two custom objects for equality.

• Ensure immutability of the custom object to prevent unexpected behavior.
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Q2. Questions on Multithreading
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Q1. Core Java Questions
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Q2. Multithreading related problem
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Q3. Write a DB query for some scenario
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Q1. Given 3 threads print a number from 1 to 10 in sequence
Ans. 
Use synchronized blocks or locks to ensure threads print numbers in sequence.
• Use synchronized blocks or locks to ensure only one thread can access the shared resource (number to be printed) at a time.

• Use a shared variable to keep track of the current number to be printed and update it after each thread prints its number.

• Use a loop to iterate from 1 to 10 and have each thread check if it is its turn to print the number.
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Q2. Core Java related questions
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Coding test with 2 questions

Q1. Best time buy and sell stocks
Ans. 
Find the best time to buy and sell stocks to maximize profit with a single transaction.
• Identify the lowest price before a peak. For example, buy at $100 and sell at $150.

• Use a loop to track minimum price and maximum profit. If price < min_price, update min_price.

• Calculate profit as current price - min_price. Update max_profit if profit > max_profit.

• Consider edge cases: if prices are always decreasing, return 0 pr...read more
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It had MCQ based Technical question

Q1. Version of React Js
Ans. 
React JS is a JavaScript library for building user interfaces.
• React JS is maintained by Facebook.

• It allows developers to create reusable UI components.

• React JS uses a virtual DOM for better performance.

• Current stable version is 17.0.2 (as of September 2021).
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Q2. Advantages of React Js
Ans. 
React Js offers fast rendering, reusable components, virtual DOM, and easy integration with other libraries.
• Fast rendering due to virtual DOM

• Reusable components for efficient development

• Easy integration with other libraries like Redux

• Support for server-side rendering for improved SEO

• One-way data binding for predictable data flow
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Q3. Hoisting, Closuers, IIF, coding questions, React Js Platform question
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Q1. What is Closures
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Q2. React Technical Round, Debouce, Bubbling, Delegation, Promises, etc
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Q1. React Technical Machine Code
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Q2. Map Filter Reduce Question, Custom Hook, Etc
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Basic java oops and coding question

Q1. DSA and java basics
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Q1. Again DSA and java advanced
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Q1. Develop chat app
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Duration was for an hour, included basic front end questions

Q1. Explain component lifecycle in React
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Q2. Write a component to display a table
Ans. 
A component to display a table in a software application
• Use HTML and CSS to create the structure and styling of the table

• Use JavaScript to populate the table with data dynamically

• Consider adding features like sorting, filtering, and pagination for better user experience
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