Diebold Nixdorf Java Consultant Interview Questions and Answers

Q1. What is OOP Concepts
Ans. 
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. How annotation works?
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Annotations in Java provide metadata about a program that can be used by the compiler or at runtime.
• Annotations start with the @ symbol.

• Annotations can be used to provide information to the compiler or to runtime environments.

• Annotations can be used to define custom metadata for classes, methods, fields, etc.

• Annotations can also be used for code generation, documentation, and validation.

• Examples of annotations in Java ...read more
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Q2. CondurentSkipListMap, how does it work
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ConcurrentSkipListMap is a concurrent, sorted map implementation in Java.
• ConcurrentSkipListMap is a concurrent version of SkipListMap, which is a sorted map implementation based on skip list data structure.

• It allows multiple threads to access and modify the map concurrently.

• It provides logarithmic time complexity for most operations, making it efficient for concurrent access.

• Example: ConcurrentSkipListMap
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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. Java vs Javascript , Meaning of Synchronization in Java , Multihreading in Js
Ans. 
Java is a backend language, Javascript is a frontend language. Synchronization in Java ensures only one thread can access a resource at a time. JavaScript is single-threaded but can handle asynchronous operations using callbacks, promises, and async/await.
• Java is a backend language used for server-side development, while JavaScript is a frontend language used for client-side scripting.

• Synchronization in Java is a techn...read more
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Q2. Write a pojo class to display the Employee Details,Pojo vs Bean
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A Pojo class is a simple Java class that contains only private fields, public getters and setters, and no-arg constructor.
• Create private fields for employee details like name, id, salary, etc.

• Generate public getters and setters for each field.

• Include a no-arg constructor in the class.

• Example: public class Employee { private String name; private int id; public String getName() { return name; } public void setName(String...read more
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Q3. How to to compare two objects with same class (equals & Hashcode methods)
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To compare two objects with the same class, override the equals and hashCode methods in the class.
• Override the equals method to compare the fields of the objects for equality.

• Override the hashCode method to generate a unique hash code based on the object's fields.

• Ensure that the equals and hashCode methods are consistent with each other.

• Example: public class Person { private String name; private int age; }
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Q4. Springboot questions basics like How to connect to 2 databases at a time How to change the table name in entity class(@Table)
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Q5. JPA Repository inbuilt methods
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JPA Repository provides inbuilt methods for common database operations in Spring applications.
• JPA Repository provides methods like save(), findById(), findAll(), deleteById(), etc.

• These methods help in performing CRUD operations on entities without writing custom queries.

• For example, userRepository.save(user) saves a user entity to the database.
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Q1. Asked basic technical questions
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Q1. Mid level technical questions
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Q1. Explain your Project. What features you have made Git related questions like code merge pull Jira tool Java questions mostly from collectiions Springboot related question Then some design pattern.
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Basic aptitude questions

Basic coding questions

Q1. Asking basic questions
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Q2. Java pattern program
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Q3. String in build program
Ans. 
String in build program refers to the process of concatenating multiple strings to create a final output.
• Use StringBuilder or StringBuffer for efficient string concatenation.

• Avoid using '+' operator for concatenating large number of strings.

• Consider using String.format() for formatting strings with placeholders.
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Q4. Java basic concepts
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Java basic problems , Array , Collections, String , Java 8 , Spring Boot,String MVC

Q1. Tell me about your Project ?
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Q2. Write a code which count the number of String (words) occurrence in sentence ?
Ans. 
Count the occurrence of each word in a sentence using Java code.
• Split the sentence into an array of words using split() method.

• Create a HashMap to store each word and its count.

• Iterate through the array and update the count in the HashMap.

• Print the word and its count at the end.
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