Top 50 back-end experienced developer interview questions and answers in 2023

Back-End Developer interview questions and answers in 2023:

Are you a back-end developer getting ready for an interview? Are you  a company recruiter who is looking  an expert back-end developer?  The blog related to back-end developer interview questions and answers for beginners and experienced professionals should be useful for you to either prepare to take interview or to appear for the back-end developer interview. 

A back-end developer is necessary for any company that relies on technology and has a user-facing website or application. Maintaining the numerous databases and setting up all the data on the server to run the client-facing portion of the website or application are the responsibilities of a back-end developer. This include taking care of the API, data and application integration, and fundamental application logic. 

The need for back-end developers is currently high. To meet the problems provided by the epidemic, the vast majority of businesses have shifted online, so there is a greater demand than ever for highly specialized back-end developers who can harness technology and keep things operating. It is projected that the hiring of specialist engineers, such as back-end developers, will increase over time.

In order to be hired as a back-end developer, you must master the back-end developer interview questions and answers . The back-end developer interview questions are related to technology like Java , Spring Boot , Microservices and Databases like Oracle , PostgreSQL, Cassandra , Mongo DB, Application Security, Application Development and Deployment process, Application Integration Testing . We have provide the below given back-end developer technical interview questions and answers  covering all the technical topics to ensure you are interview-ready.

What is object-oriented programming and its features ?

A programming language structure referred to as object-oriented programming, or OOPs, is one in which the data and the accompanying processing, known as methods, are described as independent entities also referred as objects. The main goal of object-oriented programming is to model a system made up of various objects, each of which stands for a different component of the system. The OOPs programming language is now widely utilized by developers. It gives developers a set of ideas and guidelines for making and managing objects. OOPs provides polymorphism, inheritance, data abstraction, and encapsulation as the main features of object-oriented programming.

Polymorphism refers to the existence of many different forms. Polymorphism can be simply defined as a message’s capacity to be presented in multiple forms. Compile-time or Build-time polymorphism is the process of binding an object’s functionality at the time of build. Java determines the method to call at compile time by examining the method signatures. Runtime polymorphism is the process of binding an object to functionality during runtime. Method overriding can be used to achieve runtime polymorphism. The appropriate method to invoke is decided by the Java virtual machine at runtime rather than during compilation. It is also known as late binding or dynamic binding 

Encapsulation is the process which helps in hiding the sensitive data from the users. For instance, the below class includes member variables and member functions where the member variable person name and age are declared as private which restricts the outside world to declare class member variable.

Inheritance is the process in which one class inherits the attributes of another class. Inheritance can be classified as given below:

Base Class / Super Class: The class from which attributes are inherited

Derived Class / Sub Class: The class which inherits the attribute from base / super class

What is REST API ?

A REST API, commonly referred to as a RESTful API, is a web API that complies with the restrictions of the REST architectural style and enables communication with RESTful web services. Roy Fielding, a computer scientist, came up with the term “REST,” which stands for “representational state transfer.”

A set of definitions and protocols known as an API are used to create and integrate application software. It is frequently referred to as a contract between a source of information and a user of that information, defining the content that the consumer (the request) and the producer (the response) are expected to provide. For instance, the API architecture for a weather service would need the user to provide their zip code and the producer to respond with a pair of parameters: the high temperature and the low temperature.

What is Microservices architecture ?

The architecture of microservices is made up of explicitly defined, loosely packed components. Here, unlike in monolithic architecture, each unit carries out its specific tasks. These can be used in various ways depending on the user’s needs. They are particularly effective in fixing the flaws in monolithic architecture. By breaking complicated systems up into smaller services, micro-services architecture aims to make it simpler to design complex applications. Every part of a microservice is distinct from other parts since it has its own CPU, environment, and development team. All of this implies that each component may operate, function, and communicate without relying on any other components.

Provide some Advantages of Microservices Architecture ?

The below given are the major advantages of Java Microservices Architecture: 

Reduces development effort: Multiple microservices can be created and developed simultaneously since it uses distributable development, which enables an increasing number of developers to work on the same service at once and shorten the time it takes to build.

Loosely coupled components:  Small modules that were written independently with their own separate code make up the microservices architecture. These services may not share the same stack or framework and are loosely coupled and entirely independent. As a result, they can be created and changed independently. 

Ease of Deployment: It is relatively simple to deploy microservice-based systems because they are significantly smaller and simpler than conventional monolithic ones. The developer can experiment with various types of logic or business procedures thanks to this capability. If a service isn’t meeting needs, one can replace it with a different, comparable service.

Provides flexibility:  A  Full Stack is a collection of several tools used together to create software or a program. They can be combined to create a microservices technology stack, which consists of numerous services that collaborate and offer flexibility because a centralized system will no longer be required to manage it. Instead, it could be altered or adjusted to suit our needs in order to create an entirely new experience.

Provides Isolation: One of the biggest benefits of microservices design is that a service issue can be isolated without affecting other services. For instance, even if a consumer is unable to upload a photo, he can still explore, update, and perform other actions on the web application. As a result, it prevents total failure and can partially resolve a single broken service.

Provides scalability : The microservices are easier to scale because of its architecture with minimal cost of the infrastructure. 

What is an Reverse Proxy?

A reverse proxy is a sort of proxy that allows users to retrieve data from other services on their behalf. It provides data to clients in a way that makes it appear as though it came from the reverse proxy server. Reverse proxies are mostly utilized to distribute the load.

What is the difference between GET and POST HTTP Methods ?

  • Data is retrieved from a web server via a GET query. Data is sent to a web server via a POST query.
  • A GET request sends URL parameters. The body of a POST request contains the request’s parameters.

What are the Core Spring Framework Annotations ?

The below are the commonly used Spring Framework annotations  

@Required: The bean setter method applies the @required annotation. The annotated bean must have the necessary attribute populated at configuration time in order to avoid throwing an BeanInitilizationException 

@Autowired: Spring offers @Autowired annotation to support annotation-based auto-wiring. It is used to automatically wire a spring bean’s constructor, instance variables, and setter methods. The spring container automatically wires the bean when we use the @Autowired annotation by matching the data-type.

@Configuration: This annotation is at the class level. A source of bean definitions utilized by Spring Containers is the class marked with @Configuration.

@ComponentScan: This annotation is helpful while searching for beans in a package. @ComponentScan annotation is utilized with the @Configuration annotation. In order to search for Spring Components, we may optionally specify the base packages.

@Bean: This annotation is at the method level. It serves as an XML “bean” tag substitute. It instructs the process to create a bean to be managed by Spring Container

@Component: This annotation is at the class level. A Java class can be designated as a bean when applied with @Component annotation. On the classpath, a Java class with the annotation @Component is discovered. It is taken up by the Spring Framework and set up as a Spring Bean in the application context.

@SpringBootApplication: It is a combination of three annotations @EnableAutoConfiguration, @ComponentScan, and @Configuration

What are the Spring Framework Stereotype Annotations ?

The below are the commonly used Spring REST annotations

@Controller: The @Controller is a class-level annotation. It is a @Component specialization. It identifies a class as handling web requests. Web pages are frequently served using it. It typically produces a string indicating the redirection route. Typically, @RequestMapping annotation is used with it.

@Service: @service annotation is also used at class level and tells Spring that class contains the business logic

@Repository: @Repository is a  class-level annotation . The repository is a Data Access Object (DAO) that has direct access to the database. The repository handles all database-related operations.

What are the Spring REST API Annotations ?

The below given are the commonly used Spring based REST API annotations 

@RequestMapping:  The web requests are mapped using the @RequestMapping attribute. It features a lot of optional components, including produces, value, path, header, method, and consumes.  @RequestMapping attribute can be used at class or method level.

@GetMapping: The annotation @GetMapping maps the HTTP GET requests on the specific handler method. The @GetMapping annotation is used to create a web service endpoint to GET the required data object. Syntax usage: @RequestMapping(method = RequestMethod.GET)

@PostMapping: The annotation maps the HTTP POST requests on the specific handler method. It is used to create a web service endpoint that CREATES the data object and sends it to the targert service which could be another web service or database. Syntax usage : @RequestMapping(method = RequestMethod.POST)

@PutMapping: The annotation maps the HTTP PUT requests on the specific handler method used to create a web service endpoint that CREATES or UPDATES the data object. Syntax usage: @RequestMapping(method = RequestMethod.PUT)

@DeleteMapping: The annotation maps the HTTP DELETE requests on the specific handler method used to create a web service endpoint that DELETES a resource. Syntax usage: @RequestMapping(method = RequestMethod.DELETE)

@PatchMapping: The annotation maps the HTTP PATCH requests on the specific handler method. Syntax usage: @RequestMapping(method = RequestMethod.PATCH)

@RequestBody: The annotation is used to bind HTTP request with an object in a method parameter. The body of the request is converted internally by using HTTP MessageConverters. The Spring framework binds the incoming HTTP request body to that parameter.

@ResponseBody: The annotation binds the method return value to the response body. The Spring Boot Framework serializes the return an object into JSON and XML format.

@PathVariable: The annotation, @PathVariable, is used to retrieve values from the URI and is preferred for RESTful web services if the path variable is present in the URL.

@RequestParam: The annotation @RequestParam or also called as query parameter is used to extract the URL’s query parameters. If the URL doesn’t contain the query parameter, it can specify default values.

@RequestHeader: The annotation is used to get the HTTP request headers details. The optional elements of the annotation are name, required, value, default value.

@RestController: The annotation can be considered as a combination of @Controller and @ResponseBody annotations.

@RequestAttribute: The annotation binds a method parameter to request attribute.

What are the different bean types available in spring framework?

singleton scope The bean instance is created only once and same instance is returned by the IOC container.
The singleton scope is the default scope.
prototype scope The new bean instance is created each time when requested.
request scope The new bean instance is created per HTTP request.
session scope The new bean instance is created per HTTP session.
globalsession scope The new bean instance is created per HTTP global session. It can be used in portlet context only.

What are the types of IOC container and their role in spring?

The below given are the types of IOC containers provided by the spring framework.

  • BeanFactory
  • ApplicationContext

BeanFactory is the basic container whereas ApplicationContext is the advanced container. ApplicationContext extends the BeanFactory interface. ApplicationContext provides more facilities than BeanFactory such as integration with spring AOP, message resource handling for i18n etc

IOC container is responsible to

  • create the instance
  • configure the instance
  • assemble the dependencies

Provide the difference between Constructor Injection and Setter Injection ?

No.Constructor InjectionSetter Injection
1)Constructor injection does not provide partial injectionSetter Injection provides partial injection
2)Constructor injection does not override the setter propertySetter Injection overrides the constructor property if both are defined.
3)Creates new instance if any modification occursSetter Injection doesn’t create new instance if you change the property value
4)Constructor injection is useful when we have many
properties required
Setter Injection is useful when few properties are required

What are the different types of AOP implementation ?

Spring provides 3 types of differnt AOP implementation

  • Spring AOP
  • Apache AspectJ
  • JBoss AOP

Mention the classes for spring JDBC API ?

The below given are the Spring provided JDBC API classes

  • JdbcTemplate
  • SimpleJdbcTemplate
  • NamedParameterJdbcTemplate
  • SimpleJdbcInsert
  • SimpleJdbcCall

What are the query methods provided by spring JdbcTemplate to fetch records from the database ?

The below given query methods are provided by spring JdbcTemplate to fetch records from the database

  • ResultSetExtractor
  • RowMapper

Describe the Spring provided transaction management ?

One of the strongest arguments for using the Spring Framework is its extensive transaction support. Java Transaction API (JTA), JDBC, Hibernate, Java Persistence API (JPA), and Java Data Objects (JDO) all use a consistent programming architecture. The following advantages of the Spring Framework’s consistent abstraction for transaction management are provided:

Programmatic transaction management: Transaction management via programming is referred to as programmatic transaction management. Although it gives you great flexibility, it is challenging to keep up.

Declarative transaction management : Declarative transaction management implies that you separate transaction management from the business code. To manage the transactions, only XML-based settings or annotations are used.

What are the methods provided by PlatformTransactionManager ?

Spring transaction abstraction is defined by the org.springframework.transaction.PlatformTransactionManager interface

public interface PlatformTransactionManager {
   TransactionStatus getTransaction(TransactionDefinition definition);
   throws TransactionException;
   void commit(TransactionStatus status) throws TransactionException;
   void rollback(TransactionStatus status) throws TransactionException;
Transaction Method Name Transaction Method Description 
TransactionStatus getTransaction(TransactionDefinition definition)The method returns a currently active transaction or creates a new one
void commit(TransactionStatus status)method commits the given transaction
void rollback(TransactionStatus status)method performs a rollback of the given transaction

What are the possible values for the transaction isolation level by Spring Transaction management ?

The below given are the different types of isolation level provided by Spring Transaction management. 

Transaction Isolation value Transaction Isolation Description
TransactionDefinition.ISOLATION_DEFAULTprovides the default isolation level 
TransactionDefinition.ISOLATION_READ_COMMITTEDIndicates that dirty reads are prevented; non-repeatable reads and phantom reads can occur
TransactionDefinition.ISOLATION_READ_UNCOMMITTEDIndicates that dirty reads, non-repeatable reads, and phantom reads can occur
TransactionDefinition.ISOLATION_REPEATABLE_READIndicates that dirty reads and non-repeatable reads are prevented; phantom reads can occur.
TransactionDefinition.ISOLATION_SERIALIZABLEIndicates that dirty reads, non-repeatable reads, and phantom reads are prevented

How continuous integration and continuous delivery can be useful in distributed applications ?

Two methods in software engineering—continuous integration and continuous delivery are tied to one another. Continuous integration is a procedure that ensures the program is built and tested frequently on an ongoing basis. Contrarily, continuous delivery refers to the ongoing development process that occurs in the latter stages of a program’s lifespan, immediately before production.

Through the elimination of inconsistencies between the development and operations teams, these two processes combine to generate a seamless automated process that keeps the job on schedule and boosts production speed.

Explain the Thread life cycle in java ?

The thread goes through the below given life cycle states : 

New: When the thread object is created using a new operator . The thread is created but cannot be started until  the start() method is invoked
Runnable: When the thread object is ready to run after calling the start() method. 
Running: When the thread  scheduler picks the thread from the ready state, and the thread is running.
Waiting/Blocked: When the thread object is not running but still alive, or it is waiting for the other thread to complete. 
Dead/Terminated: When the thread object is in terminated or dead state when the run() method exits

Provide few advantages of multithreading in java ?

The below given are the advantages of multithreading in java

  • Multithreading enables a program or application to always be responsive to input even when operating with certain background processes, 
  • Tasks can be completed more quickly thanks to multithreading because each thread operates on its own.
  • As threads share the same memory resources, multithreading improves the usage of cache memory.
  • Multithreading minimizes the number of servers needed.

Explain inter-thread communication in java ?

Inter-thread communication depicts the  communication between synchronized threads. In Java, thread polling is avoided by using inter-thread communication. The thread is paused running in its critical section, and another thread is allowed to enter (or lock) in the same method for execution. It can be obtained by wait(), notify(), and notifyAll() methods

Explain the use of wait () in threads in java?

The object class wait() function is used to pause the currently running thread and wait for another thread to call the notify() function. It should be noted that in order to prevent an exception from occurring, the wait() method must be called from a synchronized block. Current thread releases the lock and enters the wait state after using wait().

What is the difference between wait () and sleep() in java ?

1) The wait() method is defined in Object class.The sleep() method is defined in Thread class.
2) The wait() method releases the lock.The sleep() method doesn’t release the lock.

Provide some details about the daemon thread in java ?

The daemon threads, which have a low priority, give the user threads assistance and services in the background. If the program only uses the daemon thread and all other user threads are terminated or killed, the daemon thread is immediately stopped by the JVM.

The below given are the methods for daemon thread available in the Thread class:

  • public void setDaemon(boolean status): It used to mark the thread daemon thread or a user thread
  • public boolean isDaemon(): It checks the thread is daemon or not.

How to achieve scalability in complex web based applications ?

Scalability is a crucial factor to take into account when trying to increase productivity, especially when it comes to meeting increased user expectations and adapting features and components to larger volumes of user data. One must examine a software program’s scalability to ascertain its lifetime worth.

Lack of scalability necessitates replacing the application with a new tech stack that can accommodate the increase in user base. Features like application data caching, application states, API development using microservices architecture , data sorting mechanism , and asynchronous programming can improve a program’s scalability.

Explain the DRY and DIE Principles with respect to data redundancy ?

  • DRY (Don’t Repeat Yourself) is a software development guideline that states that developers shouldn’t reuse their own code. Multiple updates are required when there is duplicate code, which can lead to maintenance issues.
  • DIE (Duplication Is Evil) goes one step farther than the DRY principle and asserts that even little quantities of duplication ought to be avoided.

In which situation caching should be considered in distributed applications ?

Caching is frequently used to boost an application’s performance. For instance, frequently used data from a database might be cached to reduce the number of needless searches.

How the data can be optimized in the Database ?

Maintaining an efficient database is crucial process that needs to be maintained  periodically. The database optimization process can be carried out by executing maintenance operations on a regular basis, such as indexing the data or deleting outdated material that is no longer required. It’s also important to keep checking on the database’s performance to make sure it can support the load of the application.

Which are the possible ways to prevent SQL injection risks?

As a back-end developer , the below given approaches can be followed: 

  • Use parameterized queries and prepared statements in your java code 
  • In case of database SQL queries, prefer to  use stored procedures and call them when necessary to prevent dynamic generation.
  • Prefer Utilize white list input validation 

Explain the performance testing process for the microservices application ?

The below given steps need to be considered for the performance testing : 

  • Determine the testing environment
  • Determine the performance metrics
  • Prepare for performance evaluations
  • Set up the testing environment
  • Prepare  the test plan for all required business scenarios
  • Run the tests
  • Test analysis, report writing, and retesting 

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