20+ Java Technical Lead Interview Questions and Answers

Classes, variables, and objects are stored in different areas of JVM's memory.

• Classes are stored in the method area of JVM's memory.

• Variables are stored in the stack or heap depending on their scope and lifetime.

• Objects are stored in the heap area of JVM's memory.

• Static variables are stored in the method area.

• Local variables are stored in the stack.

• Instance variables are stored in the heap.

• Primitive data types are stored in the stack.

• References to objects are stored in the st...read more

To convert checked exception to unchecked exception, use RuntimeException or create a custom unchecked exception.

• Use RuntimeException to wrap checked exceptions and throw them as unchecked exceptions

• Create a custom unchecked exception by extending RuntimeException class

• Use try-catch block to catch checked exceptions and throw them as unchecked exceptions

Streams in Java and conventions for REST API. Spring MVC error handling and Spring Boot configuration annotations.

• Streams are a sequence of elements that can be processed in parallel or sequentially.

• To get distinct objects, use the distinct() method.

• Conventions for REST API include using HTTP methods, status codes, and resource naming.

• Spring MVC error handling can be done using @ExceptionHandler annotation.

• Spring Boot configuration annotations include @Configuration, @EnableA...read more

Stream is sequential while parallel stream is concurrent

• Stream is a sequence of elements that can be processed sequentially

• Parallel stream is a sequence of elements that can be processed concurrently

• Parallel stream can improve performance for large datasets

• Parallel stream uses multiple threads to process elements in parallel

• Stream is suitable for small datasets or when order of processing is important

2 way SSL is needed for mutual authentication between client and server.

• 2 way SSL ensures that both client and server are authenticated

• It provides an extra layer of security by verifying the identity of both parties

• It is commonly used in financial transactions, healthcare, and government applications

Controller Advice is a mechanism in Spring MVC to handle exceptions globally.

• It is used to handle exceptions across multiple controllers.

• It can be used to add common data to the model.

• It can be used to customize the response status code and message.

• It can be used to redirect to a custom error page.

Grouping by in streams in Java

• Use the 'groupingBy' method from the 'Collectors' class

• Pass a lambda expression to specify the grouping criteria

• The result is a Map with the grouping criteria as keys and the grouped elements as values

Decorator pattern adds behavior to an object dynamically without affecting its existing behavior.

• It is a structural pattern

• It involves a component interface, concrete component, decorator interface, and concrete decorator

• Decorators wrap around components to add new behavior

• It allows for flexible and dynamic behavior modification

• Example: Java I/O streams use decorator pattern

Kafka is a distributed streaming platform used for building real-time data pipelines and streaming applications.

• Kafka is used for building real-time data pipelines and streaming applications

• Kafka Streams is a client library for building applications and microservices that process streams of data

• Kafka provides fault-tolerant storage and processing of streams of records

• Kafka Streams allows for stateful and stateless processing of data

• Kafka can be used for various use cases such...read more

Using Streams API to find occurrence of each element in an array of strings

• Use Arrays.stream() to convert the array to a stream

• Use Collectors.groupingBy() to group elements by their occurrences

• Use Collectors.counting() to count the occurrences of each element

Java 8 introduced lambda expressions, streams, default methods, and more.

• Lambda expressions for functional programming

• Streams for efficient processing of large data sets

• Default methods to add new functionality to existing interfaces

• Date and Time API for improved handling of date and time

• Optional class to avoid null pointer exceptions

• Nashorn JavaScript engine for improved performance

• Parallel array sorting for faster sorting of large arrays

CopyOnWriteArrayList is a thread-safe variant of ArrayList that creates a new copy on modification.

• 1. Thread-Safety: It allows concurrent read operations without locking, making it suitable for multi-threaded environments.

• 2. Copy on Modification: When a write operation (like add or set) occurs, it creates a new copy of the underlying array.

• 3. Performance: Read operations are fast, but write operations can be costly due to array copying.

• 4. Use Case: Ideal for scenarios with mo...read more

Improving microservice security involves implementing authentication, authorization, encryption, and monitoring.

• Implement strong authentication mechanisms such as OAuth or JWT

• Use role-based access control for authorization

• Encrypt sensitive data in transit and at rest

• Implement monitoring and logging to detect and respond to security incidents

Sort strings based on city names.

• Use Arrays.sort() method with a custom Comparator to sort strings based on city names.

• Create a Comparator that compares the city names of two strings.

• Example: String[] cities = {"New York", "London", "Paris"};

• Example: Arrays.sort(cities, (a, b) -> a.compareTo(b));

Producer-consumer pattern in Kafka involves producers sending messages to topics and consumers reading from those topics asynchronously.

• Producers publish messages to Kafka topics, which act as message queues.

• Consumers subscribe to topics and process messages independently.

• Kafka ensures message durability and fault tolerance through replication.

• Example: A web application (producer) sends user activity logs to a Kafka topic, while a data processing service (consumer) reads and ...read more

Find 2nd max element in an array of strings.

• Sort the array in descending order

• Return the element at index 1

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 when the client knows the URI of the resource it wants to update.

• POST is used when the client does not know the URI of the resource it wants to create.

Microservices with Kubernate deployment involves breaking down an application into smaller, independent services and deploying them using Kubernetes.

• Microservices architecture involves breaking down a monolithic application into smaller, independent services that can be developed, deployed, and scaled independently.

• Kubernetes is a container orchestration platform that automates the deployment, scaling, and management of containerized applications.

• Deploying microservices with ...read more

Using static in main function allows it to be called without creating an instance of the class.

• Static in main function allows it to be called directly without creating an object of the class.

• Static methods can be called using the class name itself, without creating an object.

• Example: public static void main(String[] args) { }

Microservices are a software development technique where applications are composed of small, independent services that communicate over well-defined APIs.

• Microservices break down a large application into smaller, loosely coupled services

• Each service is responsible for a specific function and can be developed, deployed, and scaled independently

• Communication between services is typically done through APIs, often using lightweight protocols like HTTP or messaging queues

• Microserv...read more

HashMap is a data structure that stores key-value pairs and uses hashing to efficiently retrieve values.

• HashMap internally uses an array of linked lists to store key-value pairs.

• When a key-value pair is added, the key is hashed to find the index in the array where it will be stored.

• If multiple keys hash to the same index, a linked list is used to handle collisions.

• Retrieving a value involves hashing the key to find the index and then traversing the linked list to find the val...read more

Design a database table for storing user information

• Identify the necessary fields such as name, email, phone number, address, etc.

• Define appropriate data types for each field (e.g. VARCHAR, INT, DATE)

• Set primary key and any necessary constraints (e.g. unique, not null)

• Consider normalization to avoid data redundancy and improve data integrity

RestAPI implementation involves creating web services using HTTP methods to interact with data.

• Use HTTP methods like GET, POST, PUT, DELETE to perform CRUD operations on resources

• Implement endpoints with appropriate request and response formats (JSON, XML)

• Secure API with authentication and authorization mechanisms like OAuth

• Document API using tools like Swagger for easy consumption by clients

The thread life cycle in Java describes the various states a thread can be in during its execution.

• New State: A thread is created but not yet started. Example: Thread t = new Thread();

• Runnable State: The thread is ready to run and waiting for CPU time. Example: t.start();

• Blocked State: The thread is waiting for a monitor lock to enter a synchronized block or method.

• Waiting State: The thread is waiting indefinitely for another thread to perform a particular action. Example: t....read more