Backend Developer Interview Questions and Answers Web Development

Object-oriented programming, commonly known as OOP, refers to a programming language structure in which the data and the associated processing, called methods, are defined as self-contained entities. The entities are known as objects. Object-oriented programming is all about modelling a system consisting of several objects, and each object represents a particular aspect of the system. OOP language is widely used by developers in recent times. It offers a set of concepts and rules to the developers for the creation and management of objects. The four main fundamental concepts of OOP include polymorphism, inheritance, data abstraction, and encapsulation.

This is a frequently asked question in backend developer interview questions for freshers.

This is one of the common backend developer questions asked in the interviews. It is mainly asked of young developers who are in the early stages of their careers. It is an obvious fact that, as a beginner, you may not be proficient in all the languages and skills that are required in backend development. However, by asking this question, the interviewer wants to evaluate your enthusiasm and curiosity. The interviewer will see how much you know about the programming languages you prefer to work with. An important point to remember here is that there is no best language. Different languages are suitable for different tasks. You can explain your preferred languages and how they help carry out specific tasks.

The lack of strict separation between the codes or program instructions and external or user-provided input results in injection attacks. It enables attackers to attack data snippets by injecting malicious codes. SQL injection is a common injection attack. To carry out this attack, malicious SQL statements are used by the attacker. SQL injection can be prevented in a number of ways. Some of the different ways to prevent the attack are: 

• Stored procedures 
• Input validation – It includes both whitelist validation and blacklist validation. 
• Prepared statements with the use of parameterized queries. 
• Principle of least privilege 

There exists a significant difference between the functional test and the acceptance test. Functional testing refers to the verification activity. It checks whether a product has been designed in the right manner for optimal functionality or not. It also tests whether that software can meet the intended business requirements. Functional testing focuses on verifying whether the product functions in the desired manner. On the other hand, acceptance testing is the validation activity. It checks whether the right thing has been built or not. Acceptance testing evaluates whether the product is able to solve the problems of the customers or not.

There are a number of benefits of web services. Some of the prominent benefits are: 

• Reusability – A single web service can be used by a number of client applications at the same time. 
• Interoperability – Web services can be accessed through the network. It uses XML/ JSON for transporting data and runs on HTTP/ Soap protocol. It can be easily developed using any programming language.  
• Easy to integrate and deploy – Integration and deployment of web services can be done much more easily and in less time. 
• Multiple service versions – A number of service versions can run at the same time.  
• Loose coupling – The client code of web services is independent of server code. So, the loose coupling can be achieved in the application.  

This is one of the common backend developer interview questions that you are likely to come across in the interviews. It tests the fundamental knowledge of the candidates. Performance testing is the testing technique that evaluates the responsiveness, scalability, stability, and speed of the applications. It tests how well an application can perform under different load conditions. The different steps involved in performance testing are: 

• Identification of the testing environment 
• Identification of performance metrics 
• Planning and designing of performance tests 
• Configuration of test environments 
• Implementation of the test design 
• Execution of the tests 
• Analysis and reporting of the test results. 

Expect to come across this popular question in junior backend developer interview questions.

In order to ensure better outcomes of performance testing, it is vital to have knowledge of the best practices. Some of the best practices of performance testing are: 

• Conduct the performance test as early as possible during the development stage 
• Test the software units separately first and then test the units together 
• Baseline measurements should be the starting point of performance testing
• Conduct a number of performance tests in order to ensure consistent findings 
• Keep the test environment of performance tests consistent 
• Isolate the environment of performance testing from the environment suitable for the quality assurance testing 
• Calculate averages in order to get actionable metrics.

Software architecture is all about creating the structure of the program. In order words, it is referred to as the bare skeleton of the software program. On the other hand, software design involves the process of implementing codes to meet the software requirements. Software architecture is the blueprint of the program, while software design is the process of building the program. Both software design and software architecture are two different processes that work together to form an integrated development process.

Scalability is considered to be an important aspect of ensuring improved productivity of software programs. It is mainly related to high user demands. It ensures that the software program is able to adapt different functions well when the amount of user data increases. Checking the scalability helps in determining the lifetime validity of the software programs. If a software program is not scalable, it will not be able to function properly with the increase in audience. In case of a lack of scalability, there is a need to rewrite the application to ensure that it adapts well to the growth in audience. The features such as API, states, cache, etc., can help in increasing the scalability of the software programs.

When there is no live code testing, interviewers usually ask such questions in order to gain insights into your practical knowledge about backend development. There does not exist any concept such as perfect code. Debugging is important to identify potential flaws in a software program. It is the process of identifying the bugs and fixing them at the right time to ensure the optimum performance of the application. While answering this question, you will have to name a few debugging tools that you use to fix the issues in the applications. You also need to mention the different steps for fixing the potential issues. Remember, different bugs are handled in different manners. So, you need to answer this question accordingly.

A clustered index involves storing the rows physically on the disk in the same order as they appear on the index. Therefore, there can be only one clustered index. The clustered index mainly tells the database to store values present next to one another on the disk. On the other hand, a non-clustered index consists of a second list with pointers to the different physical rows. Unlike a clustered index, there can be a number of non-clustered index. With the increase in new indexes, the time required for writing new records also increases.

In Java, an immutable class refers to a class that cannot be modified after its creation. Some of the ways of creating an immutable class are: 

• Declare the class as final to avoid the creation of child classes. 
• Declare the data members present in the class as final to ensure that the values do not change after the creation of the objects. 
• Declare the data members present in the class as private in order to prevent direct access.
• Perform a deep copy of different objects to return a copy and not the real object reference. 

Thread can be defined as the individual path of execution through the program codes. Threads are mainly used to increase the speed of Java applications and enhance their overall responsiveness by doing a number of things simultaneously. There are different kinds of threads used. The two prominent kinds of threads are user threads and daemon threads. User threads refer to high-priority threads. On the other hand, the daemon threads are the low-priority threads whose role is to deliver services to different user threads.

Microservices architecture refers to the integration of a number of small but independently deployable services into a single application. It helps in increasing the versatility of operations as various programming languages are used in order to write individual services. So, one can use different languages for different services. There are a number of benefits to choosing microservices architecture. One of the most significant benefits is that it can adapt to new technologies and frameworks. Moreover, the failure of one process will not affect the functioning or operations of the entire system. Another significant benefit of microservices architecture is that it can get up and running in a very short period of time.

A common question in interview questions backend developer, don't miss this one.

ACID is the short form that is used in order to define different properties of a relational database system. ACID refers to 4 separate terms. It includes: 

• Atomicity – It refers to the property that states if one part of the transaction fails, then the whole transaction will fail. However, the database state remains unchanged. 
• Consistency – It is the property that ensures performing any transaction will move the database from one state to another. 
• Isolation – As per this property, in case two transactions are performed simultaneously, it will result in a state that would have been obtained when transactions were carried out in a sequential manner.
• Durable – The property indicates the completion of a transaction. The properties and shape of the transactions will not change even if the power goes off.

Containerization refers to the visualization strategy that is an ideal alternative to traditional hypervisor-based virtualization. Containerization involves the sharing of the operating system by a number of containers instead of being cloned for individual virtual machines.

The complexity of data is increasing a lot in recent times. NoSQL can help in resolving the issue. It can be defined as a mechanism that is used for the retrieval and storage of data. It is a type of database that can effectively handle and sort messy, complicated, and unstructured data. It can be considered as thinking in a new way about databases. There are several types of NoSQL databases. Some of the significant types include key-value, graph, document-oriented, and column-oriented.

Many developers prefer using Go programming owing to the various benefits it offers. Some of the main benefits of Go programming are: 

• Its simplicity and conciseness make it ideal for use. 
• It provides quality support for type embedding and interfaces. 
• The compilation timing of Go programming is quite fast in comparison to other programming. 
• It provides support for different environments adopting patterns that are similar to dynamic languages. 
• Go programming comes with in-built concurrency support. 

Availability can be defined as the ability of the users of an application to access the systems. In case a user is not able to access the system, it is considered to be unavailable. High availability indicates that an application will be available to the user without interruption. To achieve high availability in the case of web applications, redundant server nodes can be used along with clustering. Availability is expressed in the form of a percentage of uptime in a given year.

Availability can be defined as the ability of the users of an application to access the systems. In case a user is not able to access the system, it is considered to be unavailable. High availability indicates that an application will be available to the user without interruption. To achieve high availability in the case of web applications, redundant server nodes can be used along with clustering. Availability is expressed in the form of a percentage of uptime in a given year.

A reverse proxy can be defined as a type of proxy that can retrieve data from a number of services on behalf of clients. It returns data to the clients in such a way that it seems that data actually originated from the reverse proxy server. The reverse proxy is mainly used in order to balance the load.

Continuous delivery refers to the process of continuous integration to ensure the quick release of different changes to the customers. Apart from the automation of the testing process, the process of starting and releasing the program can also be automated.  

On the other hand, continuous integration allows the developers to merge the changes to the main branch. It helps eliminate the chaos and ensures the faster release of the software products.

Continuous deployment allows each of the shifts going through the production stages to quickly reach out to the customers.

The full form of BASE is Basically Available, Software state, Eventual consistency. The BASE properties refer to the general properties that are inherent in the NoSQL systems. It does not provide any guarantee of consistency. However, it provides a guarantee of availability. The soft structure of the system suggests that the state of the system is likely to change over time.

Mocks refer to the objects with preprogrammed expectations shaping the specifics of the call. On the other hand, stubs can be defined as the standard responses to calls that are made during the test. Stubs are capable of recording call information. For instance, the email gateway stub is capable of remembering the message it has sent. Fake objects have various working implementations. However, they will require a reduction, thereby making them unusable for production.

This is one of the common junior backend developer interview questions that you are likely to come across. Spike testing refers to a type of stress testing that involves the evaluation of the performance of software when there is a rapid increase in the workload. For a short period of time, the load is likely to exceed the expectations.

The CAP theorem was published by Eric Brewer. According to the theorem, a distributed computer system cannot simultaneously guarantee consistency, availability, and partition tolerance. Consistency is the attribute that ensures all the nodes show the same data at the same time. Availability is the guarantee that ensures all the requests will receive a response as to whether it has failed or were successful. Partition tolerance ensures that the system continues its operation despite the loss or failure of the arbitrary message. A number of top companies, such as Google, Facebook, and Amazon, use this theorem in order to decide on their application architecture.

This is also one of the common senior backend developer interview questions. Through this question, the interviewer wants to know the different types of projects that you have handled in your career as a developer. To answer this question, you will have to state one of the challenges you handled successfully. Make sure to describe the challenge in detail, along with the solution you adopted. The answer will also provide the interviewer with insights into your capability to handle the desired projects in the organization.

Serialization refers to the mechanism or method of transforming the state of an object into a byte stream. Serializing an object guarantees that the byte stream can be reverted into a copy of the actual object. In Java, serialization is often used in Hibernate, JMS, JPA, and EJB in order to ensure the effective transportation of code from one JVM to another. On the other hand, deserialization does the reverse of serialization.

A common question in backend developer interview questions and answers, don't miss this one.

This is one of the important Java backend developer interview questions. In Java, HashMap works on a number of hashing principles. It leverages the static inner liner class in order to store the entries in the map. The HashMap also makes use of different buckets, with each of the buckets pointing towards a Singly Linked List. It allows for a number of null values and one null key.

Exception handling refers to the process of responding to the exception occurrences such as RemoteException, IOException, ClassNotFound Exception, and SQLException. In Java, the two prominent types of exceptions are unchecked exceptions and checked exceptions. The programmers are responsible for handling the checked exceptions during compilation. If it is not checked, there is a chance of a compilation error. However, there is no need to handle unchecked exceptions.

Monolithic architecture is like a big container in which different components of software architecture are tightly packed and assembled together. On the other hand, SOA stands for Service-oriented architecture. It is a collection of different services that communicate with each other. The communication may involve the passing of data or the coordination of two or more services. Finally, microservices architecture refers to the architectural style that involves structuring the software application as a collection of several small autonomous services.

An API gateway refers to a server with a single-entry point into the system. It has a lot of similarities to the Façade pattern from the object-oriented design. The API gateway consists of the internal system architecture and offers an API unique to each client. It may also have other responsibilities like load balancing, monitoring, request shaping and management, authentication, caching, and static response handling.

A distribution transaction refers to any situation in which a single event leads to the mutation of two or more data sources that cannot be atomically committed. In the microservices world, it becomes more complicated as each service consists of a unit of work and the majority of the multiple services need to work together in order to ensure the optimum success of a business.

Each and every component consists of a number of layers. It helps in ensuring a clean separation of concerns. Moreover, it can also increase the ease of testing and mocking the system. Even though it is actually a very common pattern, the developers mix the layers. The mixing of web objects with the different layers makes them difficult to be accessed by the testing code.

Creating a GOD class is considered to one of the most efficient ways of hacking a program. The GOD classes come with multiple responsibilities and keep track of huge volumes of information. A single change in the code is likely to have a significant impact on the other parts of the GOD class. This can result in a chaotic situation in the services. Therefore, it is vital to avoid the GOD class.

YAGNI is the acronym of You ain’t gonna need it. It can be defined as the implementation or analysis of different things that may not be required. It is important to be careful not to spoil the needs of the clients with individual ideas of the developers.

On the other hand, KISS is the acronym for Keep it simple stupid. It refers to the fact that simple systems are easy to manage. However, simplicity does not mean less work, as a lot of knowledge is required for the implementation.

This question is a regular feature in backend developer interview questions for experienced, be ready to tackle it.

There are several mitigation strategies that developers use in order to respond to API attacks. Some of the important strategies are: 

• Distributed Denial-of-Services (DDoS) – To respond to this attack, the developers can limit the payload size and the number of requests. 
• Injection – To respond to this attack, it is possible to sanitize and validate all data present in the API requests and limit data response to prevent unintentional leakage of sensitive information.
• Cross-Site Scripting (XSS) – To respond to this attack, the input is validated, and character filtering is used. 
• Man-in-the-Middle – To respond to this attack, you can encrypt traffic in transit.

Lambda expression is an important feature in Java. It refers to a short block of code that takes into consideration and number of parameters and finally returns a value. It consists of a comma-separated list of several formal parameters enclosed in parentheses.

A design pattern refers to a general reusable or repeatable solution to the different problem that occurs in software design. They are like blueprints. The pattern shows the relationships and interactions between classes or objects.

A primitive data type refers to a predefined data type that is offered by the Java programming language. On the other hand, the wrapper classes provide a simple way of using different primitive data types such as Boolean and int. It transforms a primitive type into an object.

Some of the most popular creational design patterns are: 

• Singleton pattern 
• Builder pattern 
• Factory method pattern 
• Abstract factory pattern 
• Prototype pattern 

There are different situations when you should use MongoDB and Redis. For instance, when you have no idea about how to query the data or what schema to follow, MongoDB is the right option to use. On the other hand, when you want to increase the speed of an existing application, you need to use Redis.

In Java, a constructor refers to a special method that is used in order to initialize objects. During the creation of a class, it is usually called. The name of the constructor remains the same as its class. It also has a lot of similarities with methods syntactically.

Some of the most common constructors are: 

• Parameterized constructor 
• Default constructor 
• No Argument constructor 

UNION simply puts lines from queries after each other. However, JOIN provides a cartesian product and then subsets it.

The main difference between ArrayList and LinkedList is that ArrayList comes under the category of collection framework of various dynamic arrays that are different from standard arrays. On the other hand, LinkedList employs LinkedList Data Structure within a class with a number of variations in every element. The ArrayList elements are stored in consecutive memory locations. However, the LinkedList nodes are randomly stored in memory locations.

Some of the prominent disadvantages of REST are: 

• Maintaining the sessions is not possible. 
• As there isn’t any contract between the client and service, it requires to be communicated through means such as emails or documentation. 
• As it operates on HTTP, there cannot be any asynchronous calls. 

DIE and DRY are two important principles of software development. DIE is the acronym for Duplication is Evil. On the other hand, the full form of DRY is Don’t Repeat Yourself.

Finally refers to a code block. It is used along with a try-catch block in order to handle the exception. On the other hand, the final refers to a keyword. The keyword is used in order to mark a variable as “unchangeable”. It is also used for applying different restrictions on class, method, and parameters. In contrast, finalize refers to a deprecated method of the Object class. It is used to perform the clean-up processing before the object becomes garbage-collected.