Alcor Solutions Inc. Lead Developer Interview Questions and Answers

Q1. Explain Abstraction and Encapsulation
Ans. 
Abstraction focuses on hiding implementation details, while encapsulation bundles data and methods into a single unit.
• Abstraction allows us to focus on the essential features of an object while hiding unnecessary details.

• Encapsulation helps in data hiding by restricting access to certain components of an object.

• Abstraction is achieved through abstract classes and interfaces in Java.

• Encapsulation is implemented using ac...read more
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Q2. Explain the use of Final keyword
Ans. 
Final keyword is used in Java to declare constants, prevent method overriding, and prevent class inheritance.
• Used to declare constants - value cannot be changed once assigned

• Prevents method overriding - method cannot be overridden in child classes

• Prevents class inheritance - class cannot be extended
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Q3. Difference between == operator and equals method
Ans. 
The == operator compares memory addresses, while the equals method compares the actual content of objects.
• The == operator checks if two object references point to the same memory address.

• The equals method checks if two objects have the same content.

• Example: String str1 = new String("hello"); String str2 = new String("hello"); str1 == str2 will return false, but str1.equals(str2) will return true.
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Q4. Explain about Hash Table
Ans. 
Hash table is a data structure that stores key-value pairs and allows for fast retrieval of values based on keys.
• Hash table uses a hash function to map keys to indexes in an array.

• It provides constant time complexity O(1) for insertion, deletion, and retrieval operations.

• Collisions can occur when two keys hash to the same index, which can be resolved using techniques like chaining or open addressing.
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Q5. What is Synchronized keyword
Ans. 
Synchronized keyword is used in Java to control access to shared resources by multiple threads.
• Synchronized keyword is used to create a synchronized block of code, ensuring only one thread can access it at a time.

• It can be applied to methods or code blocks to prevent concurrent access by multiple threads.

• Example: synchronized void myMethod() { // synchronized code block }
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Q6. What is the use of volatile keyword
Ans. 
The volatile keyword in Java is used to indicate that a variable's value will be modified by different threads.
• Ensures visibility of changes to variables across threads

• Prevents compiler optimizations that could reorder code and affect variable values

• Useful for variables accessed by multiple threads without synchronization

• Example: volatile int count = 0;
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Q7. What are checked and unchecked exceptions
Ans. 
Checked exceptions are checked at compile time, while unchecked exceptions are not.
• Checked exceptions must be either caught or declared in the method signature using 'throws' keyword

• Unchecked exceptions do not need to be caught or declared

• Examples of checked exceptions: IOException, SQLException

• Examples of unchecked exceptions: NullPointerException, ArrayIndexOutOfBoundsException
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Q8. Difference between Interface and Abstract class
Ans. 
Interface is a blueprint of a class with only abstract methods, while abstract class can have both abstract and concrete methods.
• Interface cannot have method implementations, while abstract class can have both abstract and concrete methods.

• A class can implement multiple interfaces but can only extend one abstract class.

• Interfaces are used to achieve multiple inheritance in Java, while abstract classes are used to provi...read more
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Q9. Explain Dead lock in multi threading
Ans. 
Deadlock in multithreading occurs when two or more threads are waiting for each other to release resources, resulting in a standstill.
• Deadlock happens when two or more threads are blocked forever, waiting for each other to release resources.

• Four conditions must hold for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait.

• Example: Thread 1 holds resource A and waits for resource B, while...read more
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Q10. How to achieve thread safety in java
Ans. 
Thread safety in Java can be achieved by using synchronization, locks, volatile keyword, and thread-safe data structures.
• Use synchronized keyword to create synchronized blocks or methods

• Use locks from java.util.concurrent.locks package like ReentrantLock

• Use volatile keyword to ensure visibility of changes across threads

• Use thread-safe data structures like ConcurrentHashMap, CopyOnWriteArrayList
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Q11. Difference between PUT and POST method
Ans. 
PUT is used to update or replace an existing resource, while POST is used to create a new resource.
• PUT is idempotent, meaning multiple identical requests will have the same effect as a single request.

• POST is not idempotent, meaning multiple identical requests may have different effects.

• PUT is used to update an existing resource at a specific URI.

• POST is used to create a new resource under a specific URI.

• PUT requests ar...read more
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Q12. What are Spring Actuator
Ans. 
Spring Actuator is a set of production-ready features to help monitor and manage your application.
• Provides endpoints to monitor application health, metrics, and other useful information

• Can be used to check the status of the application, gather metrics, and even perform custom actions

• Helps in troubleshooting and monitoring the application in production environment
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Q13. How to deploy a spring boot application
Ans. 
Spring Boot applications can be deployed using various methods such as embedded servers, Docker containers, and cloud platforms.
• Deploying as a standalone JAR file using embedded servers like Tomcat or Jetty

• Building a Docker image and running the application in a container

• Deploying to cloud platforms like AWS, Azure, or Google Cloud Platform

• Using CI/CD pipelines for automated deployment
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Q14. Write a program with Java 8 to filter the employees based on salary greater than 10,000 from a list of Employee objects.
Ans. 
Program to filter employees with salary > 10,000 using Java 8.
• Use Java 8 Stream API to filter employees based on salary.

• Create a Predicate to check if salary is greater than 10,000.

• Use filter() method to apply the Predicate on the list of Employee objects.
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Q15. How to rollback a transaction in spring boot
Ans. 
To rollback a transaction in Spring Boot, use @Transactional annotation and throw an exception
• Use @Transactional annotation on the method where the transaction needs to be rolled back

• Throw an exception within the method to trigger the rollback process

• Spring will automatically rollback the transaction when an exception is thrown
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Q16. Explain Dependency Injection in spring boot
Ans. 
Dependency Injection is a design pattern in Spring Boot where the dependencies of a class are injected from the outside.
• In Spring Boot, Dependency Injection is achieved through inversion of control, where the control of creating and managing objects is given to the Spring framework.

• Dependencies can be injected into a class using constructor injection, setter injection, or field injection.

• By using Dependency Injection, ...read more
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Q17. Different ways of Dependency Injection
Ans. 
Dependency Injection is a design pattern where the dependencies of an object are provided externally rather than created within the object itself.
• Constructor Injection: Dependencies are provided through the class constructor.

• Setter Injection: Dependencies are set through setter methods.

• Interface Injection: Dependencies are injected through an interface.

• Spring Framework: Uses annotations like @Autowired for Dependency I
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Q18. Explain Security management, how to enable security for APIs.
Ans. 
Security management involves implementing measures to protect APIs from unauthorized access and ensure data integrity.
• Implement authentication mechanisms such as OAuth or API keys to control access to APIs

• Use encryption to secure data transmission between clients and APIs

• Implement rate limiting to prevent abuse and protect against denial of service attacks

• Regularly update and patch API security vulnerabilities to stay ...read more
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Q19. Explain JWT Tokens
Ans. 
JWT Tokens are a type of token used for authentication and authorization in web applications.
• JWT stands for JSON Web Token

• JWT tokens are compact, URL-safe tokens that can be easily transmitted between parties

• JWT tokens consist of three parts: header, payload, and signature

• JWT tokens are often used in stateless authentication systems

• Example: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG...read more
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Q20. How to write a test case for a private method
Ans. 
Use reflection to access and test private methods
• Use reflection to access the private method in the test case

• Set the method accessible using setAccessible(true)

• Invoke the method with the necessary parameters and assert the expected result
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Q21. Stages in Jenkins
Ans. 
Stages in Jenkins are the different steps in a Jenkins pipeline that define the actions to be executed.
• Stages help break down the pipeline into smaller, manageable sections

• Each stage can have multiple steps to be executed

• Stages can be sequential or parallel

• Common stages include build, test, deploy, and notify
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Q22. Write the singleton design pattern
Ans. 
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.

• Provide a public static method to access the instance.

• Ensure the constructor is private to prevent instantiation from outside the class.
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Q23. What is memory leaks in java
Ans. 
Memory leaks in Java occur when objects are no longer being used but are still held in memory, leading to inefficient memory usage.
• Memory leaks can occur when objects are not properly dereferenced or garbage collected.

• Common causes of memory leaks include circular references, static references, and unclosed resources.

• Examples of memory leaks include not closing database connections or file streams after use.
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Q24. Difference between String and String builder
Ans. 
String is immutable, while StringBuilder is mutable and more efficient for concatenating strings.
• String is immutable, meaning once created, it cannot be changed. StringBuilder is mutable and allows for modifications.

• String concatenation in Java creates a new String object each time, while StringBuilder modifies the existing object.

• StringBuilder is more efficient for concatenating multiple strings as it does not create ...read more
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Q25. Explain Garbage Collection in java
Ans. 
Garbage collection in Java is the process of automatically reclaiming memory that is no longer in use by the program.
• Garbage collection is performed by the JVM to free up memory occupied by objects that are no longer referenced by the program.

• It helps in preventing memory leaks and ensures efficient memory management.

• Java provides automatic garbage collection, so developers do not have to manually free up memory.

• Exampl...read more
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Q26. Difference between Array and ArrayList.
Ans. 
Array is a fixed-size data structure while ArrayList is a dynamic-size data structure in Java.
• Array is a fixed-size collection of elements of the same data type.

• ArrayList is a resizable collection that can store elements of any data type.

• Arrays require a specified size at the time of declaration, while ArrayList can grow dynamically.

• Arrays use square brackets [] for declaration, while ArrayList is a class in Java's col...read more
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Q27. Design patterns used
Ans. 
Various design patterns like Singleton, Factory, Observer, etc. are used to solve common problems in software development.
• Singleton pattern ensures a class has only one instance and provides a global point of access to it.

• Factory pattern creates objects without specifying the exact class of object that will be created.

• Observer pattern defines a one-to-many dependency between objects so that when one object changes stat...read more
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Q28. What is Rest Services
Ans. 
Rest Services are a type of web service that allows communication between different systems over HTTP using standard methods like GET, POST, PUT, DELETE.
• Rest Services are stateless, meaning each request from a client to the server must contain all the information necessary to understand the request.

• They use standard HTTP methods like GET, POST, PUT, DELETE to perform CRUD operations on resources.

• Rest Services typically...read more
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Q1. Tech questions on dot net
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Q1. To check your knowledge and communication skills
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Q1. They are not even proceeding on time with the client interview . I have to quit the process because they already took 1 week for client interview round
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Q1. Basic discussion.
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2 DSA question was asked

40 questions in 20 minutes

Q1. Stones games 2 leetcode
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Q2. Permutations of array
Ans. 
Generate all possible permutations of an array of strings
• Use recursion to generate permutations

• Swap elements to create different permutations

• Base case: when array size is 1, return array as permutation
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Q1. Project discussion
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Q1. Lookup vs graphlookup in mongodb
Ans. 
Lookup is used to perform a left outer join in MongoDB, while graphlookup is used to perform recursive graph traversal.
• Lookup is used to perform a left outer join between two collections in MongoDB.

• Graphlookup is used to perform recursive graph traversal in a collection that contains graph data.

• Lookup can only perform a single level join, while graphlookup can perform multiple levels of traversal.

• Lookup is faster than
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Q2. Count frequency of each character in string
Ans. 
Use a hashmap to count the frequency of each character in a string.
• Create a hashmap to store characters as keys and their frequencies as values.

• Iterate through the string and update the hashmap accordingly.

• Return the hashmap with character frequencies.
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Q1. Create a rest api all the way from controller to repository using NOTEPAD
Ans. 
Creating a REST API from controller to repository using NOTEPAD
• Create a controller class with mapping annotations for REST endpoints

• Implement service layer to handle business logic and interact with repository

• Define repository interface with methods for data access operations

• Use Spring Boot for easy setup and configuration

• Test API endpoints using tools like Postman
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Q2. Couldnt write custom mongodb query at repository layer in notepad which rejected my candidature.
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Q1. What is normalization
Ans. 
Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity.
• Normalization helps in minimizing data redundancy by dividing the database into multiple tables.

• It ensures data integrity by avoiding update anomalies.

• Normalization is achieved through a series of rules called normal forms, such as 1NF, 2NF, 3NF, etc.

• Example: In a database, instead of storing customer details i...read more
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Q2. What is reflection
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Reflection is the ability of a program to examine and modify its own structure and behavior at runtime.
• Allows accessing metadata of types and members at runtime

• Enables dynamic instantiation of objects

• Facilitates invoking methods dynamically
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30min Pseudo Code,Ratio and Proportion

1 hour Array,HashMap

Q1. Write a program a string is Anagram or not
Ans. 
Program to check if a string is an Anagram or not
• Create a function that takes in two strings as input

• Sort the characters in both strings and compare if they are equal

• Return true if they are anagrams, false otherwise
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Q2. How to connect mongodb with database
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To connect MongoDB with a database, you need to use the MongoDB URI and a MongoDB client library.
• Use the MongoDB URI to specify the connection details such as host, port, username, password, and database name

• Install a MongoDB client library like Mongoose for Node.js or pymongo for Python

• Use the client library to establish a connection to the MongoDB database and perform CRUD operations
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Q3. What is event listener
Ans. 
An event listener is a function that waits for a specific event to occur and then triggers a response.
• Event listeners are commonly used in web development to handle user interactions like clicks, keypresses, etc.

• They are attached to specific elements and listen for events to occur on those elements.

• Once the event occurs, the listener executes a callback function to respond to the event.

• Example: Adding a click event lis...read more
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Q4. What is polymorphism
Ans. 
Polymorphism is the ability of a function or method to behave differently based on the object it is acting upon.
• Polymorphism allows objects of different classes to be treated as objects of a common superclass.

• There are two types of polymorphism: compile-time (method overloading) and runtime (method overriding).

• Example: Inheritance in object-oriented programming languages like Java allows for polymorphism.
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Q1. How to reverse a string without using extra space
Ans. 
Use two pointers to swap characters in place
• Initialize two pointers, one at the beginning of the string and one at the end

• Swap characters at the two pointers and move them towards each other until they meet or cross

• Repeat the process until the entire string is reversed
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Q2. Find a number that not present in array in O(N) time complexity array contain only 0 to n numbers
Ans. 
Use bitwise XOR operation to find the missing number in O(N) time complexity.
• Iterate through the array and XOR all the elements with their indices and the array length.

• The missing number will be the result of XORing all the elements with their indices and the array length.
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Q3. Why should you join this company
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Q4. How many interview have you give previously and why you get rejected
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