10+ Java Technology Lead Interview Questions and Answers

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

Find second largest integer in an array without sorting or using collections.

• Iterate through array and keep track of largest and second largest integers.

• Compare each element with current largest and second largest integers.

• Return second largest integer.

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

The @Service annotation is a specialization of the @Component annotation and is used to indicate that a class is a service.

• Both @Service and @Component annotations are used to indicate that a class is a Spring-managed component.

• @Service is a specialization of @Component and is used to indicate that a class is a service layer component.

• The @Service annotation is used to add a layer of abstraction between the controller and the DAO layer.

• The @Service annotation is used to provi...read more

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.

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