20+ Java Technology Lead Interview Questions and Answers

Instance variables of an object in JVM are stored in the heap memory.

• Instance variables are stored in the heap memory allocated for the object.

• Each object has its own copy of instance variables.

• Instance variables are accessed using object references.

Factory pattern creates objects without exposing the instantiation logic, while Abstract Factory pattern provides an interface for creating families of related or dependent objects.

• Factory pattern creates objects through a common interface, while Abstract Factory pattern creates families of related objects.

• Factory pattern uses a single method to create objects, while Abstract Factory pattern uses multiple methods to create families of objects.

• Factory pattern is a single metho...read more

Many-to-many relationship in Hibernate without common columns

• Create a third table with foreign keys to both tables

• Use @ManyToMany annotation in both entity classes

• Specify the join table name and column names in @JoinTable annotation

A marker interface in Java is an interface with no methods, used to mark classes for special treatment.

• Marker interfaces are used to provide metadata to the classes implementing them.

• Examples of marker interfaces in Java include Serializable and Cloneable.

• Marker interfaces are typically empty interfaces with no methods.

PUT method updates data if available, else returns success with no changes.

• PUT method updates the resource if it exists, else creates a new resource

• If no data is provided, the server returns a success response with no changes made

• Example: PUT /users/1 with empty body will return success with no changes if user with id 1 exists

Use @PostConstruct annotation or implement CommandLineRunner interface

• Use @PostConstruct annotation on a method that needs to be executed on startup

• Implement CommandLineRunner interface and override run() method

• Add the code that needs to be executed on startup in the method annotated with @PostConstruct or in the run() method

• Example: @PostConstruct public void init() { //code to be executed on startup }

• Example: public class MyApp implements CommandLineRunner { public void run...read more

Microservices can communicate through synchronous or asynchronous protocols like REST, gRPC, or message brokers.

• Use RESTful APIs for synchronous communication

• Use message brokers like Kafka or RabbitMQ for asynchronous communication

• gRPC can be used for high-performance synchronous communication

• API Gateway can be used to manage communication between microservices

• Consider using service mesh like Istio or Linkerd for more advanced communication needs

Kubernetes follows a client-server architecture with a master node and worker nodes.

• Kubernetes architecture consists of a master node and multiple worker nodes.

• The master node manages the cluster and schedules applications.

• Worker nodes run the applications and communicate with the master node.

• Kubernetes uses etcd for storing configuration data.

• Components like kube-apiserver, kube-controller-manager, kube-scheduler, and kubelet are part of the architecture.

HTTP error codes 400 and 500 represent client and server errors respectively.

• HTTP error code 400 indicates a client-side error, such as a bad request or invalid input.

• HTTP error code 500 indicates a server-side error, such as an internal server error or database connection issue.

• Other common client-side errors include 401 (unauthorized), 403 (forbidden), and 404 (not found).

• Other common server-side errors include 503 (service unavailable) and 504 (gateway timeout).

Concurrent Hash Map is a thread-safe implementation of Hash Map.

• Uses multiple segments to allow concurrent access

• Each segment is a separate hash table with its own lock

• Segments are dynamically added or removed based on usage

• Uses CAS (Compare and Swap) operation for updates

• Provides higher concurrency than synchronized Hash Map

A composite primary key is a primary key that consists of two or more columns.

• A composite primary key is used when a single column cannot uniquely identify a record.

• It is created by combining two or more columns that together uniquely identify a record.

• Each column in a composite primary key must be unique and not null.

• Example: A table of orders may have a composite primary key consisting of order number and customer ID.

An API Gateway is a server that acts as an API front-end, receiving API requests, enforcing throttling and security policies, passing requests to the back-end services, and then passing the response back to the requester.

• Acts as a single entry point for all API requests

• Handles authentication, authorization, and rate limiting

• Can transform requests and responses

• May aggregate multiple back-end services into a single API endpoint

Kafka Streams is a client library for building real-time, highly scalable, fault-tolerant stream processing applications.

• Kafka Streams allows developers to process and analyze data in real-time as it flows through Kafka topics.

• It provides a high-level DSL for creating stream processing applications without the need for a separate processing cluster.

• Kafka Streams supports stateful processing, windowing, and joins, making it suitable for a wide range of use cases.

• Example: Using...read more

Use HashMap and HashSet to efficiently find common elements between two lists of strings.

• HashMap for Counting: Use a HashMap to count occurrences of elements in the first list. Example: For list1 = ['a', 'b', 'c'], map would be {'a': 1, 'b': 1, 'c': 1}.

• HashSet for Uniqueness: Store elements of the second list in a HashSet to ensure uniqueness. Example: For list2 = ['b', 'c', 'd'], set would be {'b', 'c', 'd'}.

• Finding Common Elements: Iterate through the HashSet and check if e...read more

PUT is used to update 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 and can result in multiple resources being created if the request is sent multiple times.

• PUT requires the client to send the entire updated resource while POST only requires the necessary fields to create a new resource.

• PUT is typically used for updating data while POS...read more

SOLID principles are a set of five design principles for writing maintainable and scalable code.

• S - Single Responsibility Principle: A class should have only one reason to change.

• O - Open/Closed Principle: Software entities should be open for extension but closed for modification.

• L - Liskov Substitution Principle: Subtypes should be substitutable for their base types.

• I - Interface Segregation Principle: Clients should not be forced to depend on interfaces they do not use.

• D - ...read more

Microservices is a design pattern where an application is broken down into small, independent services that communicate with each other.

• Each service is responsible for a specific task or feature

• Services communicate with each other through APIs

• Each service can be developed, deployed, and scaled independently

• Allows for greater flexibility, agility, and resilience

• Requires a strong focus on automation, monitoring, and testing