Persistent Systems Lead Engineer Interview Questions and Answers

Q1. What is the architecture of the Java Virtual Machine (JVM)?
Ans. 
The Java Virtual Machine (JVM) is an abstract computing machine that enables a computer to run Java programs.
• JVM is platform-independent and converts Java bytecode into machine code.

• It consists of class loader, runtime data areas, execution engine, and native method interface.

• JVM memory is divided into method area, heap, stack, and PC register.

• Examples of JVM implementations include Oracle HotSpot, OpenJ9, and GraalVM.
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Q2. What is the default connection pooling in Spring Boot, and how can it be customized?
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The default connection pooling in Spring Boot is HikariCP, which can be customized through properties in the application.properties file.
• HikariCP is the default connection pooling library in Spring Boot, known for its high performance and low overhead.

• To customize the connection pooling, you can modify properties like 'spring.datasource.hikari.*' in the application.properties file.

• For example, you can set maximum pool ...read more
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Q3. What are the best practices for optimizing a Spring Boot application?
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Best practices for optimizing a Spring Boot application
• Use Spring Boot Actuator to monitor and manage application performance

• Implement caching mechanisms like Spring Cache to reduce database calls

• Optimize database queries and indexes for better performance

• Use asynchronous processing with Spring's @Async annotation for non-blocking operations

• Profile and analyze application performance using tools like VisualVM or JProfi...read more
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Q4. What is a heap dump, and how can it be used to identify memory leaks?
Ans. 
A heap dump is a snapshot of the memory usage of a Java application at a specific point in time.
• Heap dumps can be generated using tools like jmap or VisualVM.

• They provide detailed information about objects in memory, their sizes, and references.

• Analyzing a heap dump can help identify memory leaks by pinpointing objects that are consuming excessive memory.

• Common signs of memory leaks in a heap dump include a large numbe...read more
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Q5. How can you diagonally iterate through and print the elements of a 2D array?program
Ans. 
Diagonally iterate through and print elements of a 2D array of strings.
• Use nested loops to iterate through rows and columns of the 2D array.

• Calculate the diagonal elements by incrementing row and column indices together.

• Print the elements as you iterate through the diagonal of the array.
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Q1. Many questions on JAVA, SpringBoot,Kafka
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Q2. Core JAVA, JAVA 8, Collections, Stream,Junit
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Q1. Multiple questions on Spring , Constructors, Kafka , Flatmap, Collections, Mapping
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Q2. SQL query , HashMAp
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Q1. 1Code on Palindrome
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A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward.
• Check if the string is equal to its reverse to determine if it is a palindrome.

• Ignore spaces and punctuation when checking for palindromes.

• Examples: 'racecar', 'madam', '12321'
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Q2. About kafka ecosystem . Basics of Producers/Consumer
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Q3. Primary/Qualifier/order annotations
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Write a program in react.

Q1. Optimization techniques for react
Ans. 
Optimization techniques for React include code splitting, lazy loading, memoization, and virtualization.
• Code splitting: Break down the code into smaller chunks to load only what is necessary for each page.

• Lazy loading: Load components only when they are needed, improving initial load time.

• Memoization: Cache the results of expensive function calls to avoid redundant calculations.

• Virtualization: Render only the visible e...read more
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Q2. Difference between let const and var
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let is block scoped, const is constant, var is function scoped
• let: block scoped, can be reassigned

• const: block scoped, cannot be reassigned, but its properties can be modified

• var: function scoped, can be reassigned
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Q1. Multi threading
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Q2. Collections Stream Ali
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