Diebold Nixdorf Senior Java Developer Interview Questions and Answers

1 Assignment which you need to solve in front of the interviewer

Q1. Questions on Java Streams
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Q2. Questions on springboot
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Q1. Asked basic technical questions
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Q1. Mid level technical questions
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Find the pair of numbers in the array whose sum is equal to target value

Q1. Junit vs Mockito Spring boot related questions AWS related questions Java Related Questions Coding on find the smallest second number
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Q1. What is OOP Concepts
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OOP Concepts refer to the principles of Object-Oriented Programming, including encapsulation, inheritance, and polymorphism.
• Encapsulation: Bundling data and methods that operate on the data into a single unit (object)

• Inheritance: Allowing a new class to inherit properties and behavior from an existing class

• Polymorphism: The ability for objects of different classes to respond to the same message in different ways
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Q2. What is Method Overloading and Method Overriding
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Method overloading is when multiple methods have the same name but different parameters. Method overriding is when a subclass provides a specific implementation of a method that is already provided by its parent class.
• Method overloading involves creating multiple methods in the same class with the same name but different parameters.

• Method overriding occurs in a subclass that provides a specific implementation of a meth...read more
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Q3. Servlet Life Cycle
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Q4. Spring boot annotations
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Q5. What you know about Multithreading
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Multithreading is a programming concept where multiple threads run concurrently within a single process.
• Allows for parallel execution of tasks

• Improves performance by utilizing multiple CPU cores

• Requires synchronization to prevent race conditions

• Examples: creating a GUI application with responsive UI, processing multiple requests simultaneously in a web server
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Q6. What are design patterns you follow in microservices architecture
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Some design patterns in microservices architecture include Service Registry, Circuit Breaker, and API Gateway.
• Service Registry: Allows services to dynamically discover and communicate with each other.

• Circuit Breaker: Prevents cascading failures by failing fast and providing fallback mechanisms.

• API Gateway: Acts as a single entry point for clients to access multiple microservices.

• Event Sourcing: Stores the state of a sy...read more
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Q7. What is JDK Vs JIT
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JDK is Java Development Kit, which includes tools for developing Java applications. JIT is Just-In-Time compiler, which compiles Java bytecode to native machine code at runtime.
• JDK is a software development kit used for developing Java applications.

• JIT is a component of the Java Virtual Machine (JVM) that improves the performance of Java applications by compiling bytecode to native machine code at runtime.

• JDK includes ...read more
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Q1. Basic Java Question
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Q2. Spring Boot related questions
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Q1. Design a rest API and code it.
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Design and code a REST API for a software developer interview.
• Define the endpoints and HTTP methods for the API (e.g. GET /users, POST /users)

• Implement authentication and authorization mechanisms (e.g. JWT tokens)

• Use proper status codes for responses (e.g. 200 OK, 401 Unauthorized)

• Include error handling and validation for input data

• Document the API using tools like Swagger or OpenAPI
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Q2. Questions related to JPA HIBERNATE SQL
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Q1. Discussion related to Last company Project and architecture level questions
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Q2. Write code to calculate frequency of a word using Stream API and lambda expressions
Ans. 
Calculate word frequency using Stream API and lambda expressions
• Use Stream API to convert array of strings to stream

• Use Collectors.groupingBy to group words by their frequency

• Use Collectors.counting to count the occurrences of each word
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DSA questions and programming concepts

Q1. Reverse string and optimize it
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Reverse array of strings efficiently
• Use two pointers approach to swap characters from start and end of each string

• Optimize by using in-place reversal instead of creating new strings

• Consider edge cases like empty strings or strings with only one character
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Q2. Reverse binary tree
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Q1. Salary expectations
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Q2. Joining location
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Q1. Multithreading, process and performance
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Q2. Process handling
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Q3. Coding questions
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