60+ Senior Application Developer Interview Questions and Answers

Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.

• Implement a doubly linked list to keep track of the order of keys based on their recent usage.

• Use a hashmap to store key-value pairs for quick access and update.

• When capacity is reached, evict the least recently used item before inserting a new item.

• Handle get and put operations efficiently to maintain the LRU property.

• Ensure the time complexity of operations ...read more

Autowiring in Spring Boot is a feature that allows Spring to automatically inject dependencies into a Spring bean.

• Autowiring eliminates the need for explicit bean wiring in the Spring configuration file.

• There are different modes of autowiring in Spring Boot: 'byName', 'byType', 'constructor', 'autodetect', and 'no'.

• For example, 'byName' autowiring matches and injects a bean based on the name of the bean property.

Convert a binary tree to a sum tree by replacing each node with the sum of its left and right subtrees, setting leaf nodes to zero.

• Traverse the tree in postorder fashion to calculate the sum of left and right subtrees for each node.

• Set leaf nodes to zero by checking if a node has no children.

• Update the value of each node to be the sum of its left and right subtrees.

• Return the level order traversal of the converted sum tree.

Find the node where two linked lists merge, return -1 if no merging occurs.

• Traverse both lists to find their lengths and the difference in lengths

• Move the pointer of the longer list by the difference in lengths

• Traverse both lists simultaneously until they meet at the merging point

SOLID principles are a set of five design principles in object-oriented programming to make software designs more understandable, flexible, and maintainable.

• 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: Objects of a superclass should be replaceable with objects of its subclasses without affecting the corr...read more

Optional class in Java provides a way to handle null values more effectively.

• Prevents NullPointerException by explicitly checking for null values

• Encourages developers to handle null values properly

• Improves code readability and maintainability

• Helps avoid unnecessary null checks and nested if statements

Abstract class can have method implementations, while interface cannot.

• Abstract class can have method implementations, while interface cannot

• Abstract class can have constructors, while interface cannot

• A class can implement multiple interfaces, but can only inherit from one abstract class

The @RestController annotation in Spring Boot is used to define a class as a RESTful controller.

• Used to create RESTful web services in Spring Boot

• Combines @Controller and @ResponseBody annotations

• Eliminates the need to annotate each method with @ResponseBody

Standard Java pre-defined functional interfaces include Function, Consumer, Predicate, Supplier, etc.

• Function: Represents a function that accepts one argument and produces a result. Example: Function<Integer, String>

• Consumer: Represents an operation that accepts a single input argument and returns no result. Example: Consumer<String>

• Predicate: Represents a predicate (boolean-valued function) of one argument. Example: Predicate<Integer>

• Supplier: Represents a supplier of result...read more

Abstraction in OOP is the concept of hiding complex implementation details and showing only the necessary features of an object.

• Abstraction allows developers to focus on what an object does rather than how it does it

• It helps in reducing complexity and improving code reusability

• Example: In a car object, we only need to know how to drive it (interface) without worrying about the internal engine workings (implementation)

Spring Cloud addresses issues related to microservices architecture and cloud-native applications.

• Service discovery and registration

• Load balancing

• Circuit breakers

• Distributed messaging

• Configuration management

• Fault tolerance

• Monitoring and tracing

Spring supports five bean scopes: singleton, prototype, request, session, and application.

• Singleton scope: Default scope, only one instance per Spring container

• Prototype scope: New instance created each time bean is requested

• Request scope: Bean is created once per HTTP request

• Session scope: Bean is created once per HTTP session

• Application scope: Bean is created once per ServletContext

Hibernate provides several concurrency strategies like optimistic locking, pessimistic locking, and versioning.

• Optimistic locking: Allows multiple transactions to read and write to the database without locking the data. It checks for conflicts before committing the transaction.

• Pessimistic locking: Locks the data when a transaction reads it, preventing other transactions from accessing it until the lock is released.

• Versioning: Uses a version number to track changes to an entit...read more

The @SpringBootApplication annotation is used to mark a configuration class that declares one or more @Bean methods and also triggers auto-configuration and component scanning.

• Marks a class as a Spring Boot application

• Enables auto-configuration of the Spring application context

• Performs component scanning for Spring components

• Combines @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations

Yes, it is possible to import the same class or package twice in Java, but it will not cause any issues during runtime.

• Importing the same class or package multiple times in Java will not result in any errors or conflicts.

• The Java compiler will simply ignore duplicate imports and only include the class or package once in the compiled code.

• This behavior helps in avoiding unnecessary redundancy and keeps the code clean and concise.

Java Strings are immutable to ensure data integrity, thread safety, and security.

• Immutable strings prevent accidental modification of data.

• String pool optimization is possible due to immutability.

• Thread safety is ensured as strings cannot be modified concurrently.

• Security is enhanced as sensitive information cannot be altered.

MVC components include Model, View, and Controller for organizing code in a web application.

• Model: Represents the data and business logic of the application.

• View: Represents the UI and presentation layer of the application.

• Controller: Acts as an intermediary between Model and View, handling user input and updating the Model accordingly.

• Example: In a web application, a user interacts with the View (UI), which sends requests to the Controller. The Controller processes the reque...read more

I will use try-catch blocks to handle exceptions and log the error message for debugging purposes.

• Enclose the procedure call in a try block.

• Catch the exception in the catch block.

• Log the error message for debugging purposes.

• Handle the exception appropriately based on the specific scenario.

Marker interfaces in Java are interfaces with no methods, used to mark classes for special treatment.

• Marker interfaces have no methods, they simply mark a class as having a certain capability or characteristic.

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

• Classes implementing marker interfaces can be treated differently by the JVM or other components based on the interface they implement.

A classloader in Java is a part of the Java Runtime Environment that dynamically loads Java classes into the Java Virtual Machine.

• Classloaders are responsible for loading classes at runtime based on the fully qualified name of the class.

• There are different types of classloaders in Java such as Bootstrap Classloader, Extension Classloader, and Application Classloader.

• Classloaders follow a delegation model where a classloader delegates the class loading to its parent classloade...read more

Use a routing library like React Router to manage navigation and organize components into separate pages.

• Utilize React Router to set up routes for each page and handle navigation

• Organize components into separate folders based on their functionality or page they belong to

• Consider lazy loading components to improve performance, especially with a large number of pages

When passing an object as the key in a map, extra functionality needs to be implemented to ensure proper hashing and equality comparison.

• Override hashCode() method to generate a unique hash code for the object

• Override equals() method to compare the objects for equality

• Implement Comparable interface if custom sorting is required

Functional interfaces can have only one abstract method, but can have multiple static and default methods.

• Functional interfaces in Java can have only one abstract method, but can have multiple static and default methods.

• Static methods in functional interfaces can be called using the interface name itself.

• Default methods provide a default implementation in the interface itself.

• Example: java.util.function.Function is a functional interface with one abstract method and default m...read more

Filters in MVC are components that allow pre-processing and post-processing of requests and responses.

• Filters are used to perform common functionalities like logging, authentication, authorization, etc.

• They can be applied globally to all controllers or selectively to specific controllers or actions.

• Examples of filters include Authorization filters, Action filters, Result filters, and Exception filters.

Routing in MVC pattern is handled by a routing engine which maps incoming URLs to specific controller actions.

• Routing is the process of matching incoming URLs to specific controller actions in the MVC pattern.

• Routes are defined in a routing table which maps URLs to corresponding controller actions.

• The routing engine uses the routing table to determine which controller and action should handle a particular request.

• Routes can include placeholders for dynamic segments of the URL...read more

Implemented a complex data migration from legacy system to new system

• Identified all data sources and mapped them to new system

• Developed custom scripts to transform and validate data

• Performed multiple test runs to ensure data integrity

• Coordinated with stakeholders to ensure smooth transition

Garbage collector in Java is a built-in mechanism that automatically manages memory by reclaiming unused objects.

• Garbage collector runs in the background to identify and delete objects that are no longer needed.

• It helps prevent memory leaks and optimize memory usage.

• Examples of garbage collectors in Java include Serial, Parallel, CMS, and G1.

There are three ways to communicate in LWC: event communication, public properties, and method calls.

• Event communication: Components can communicate by firing and handling events.

• Public properties: Components can communicate by passing data through public properties.

• Method calls: Components can communicate by calling methods on other components.

SQL query to retrieve top 10 salaries from employee table.

• Use SELECT statement to retrieve data from employee table

• Use ORDER BY clause to sort the data in descending order based on salary

• Use LIMIT clause to limit the result set to top 10 salaries

Use synchronization mechanisms like barriers or join to aggregate parallel threads

• Use synchronization mechanisms like barriers or join to wait for all threads to complete before proceeding

• Implement a barrier that blocks all threads until they all reach a certain point in the code

• Use a join operation to wait for all threads to finish before continuing execution

To swap the value of two variables without using a third variable, use arithmetic operations.

• Use addition and subtraction to swap values

• Example: a = 5, b = 10. a = a + b (a = 15), b = a - b (b = 5), a = a - b (a = 10)

JS works by interpreting and executing code line by line, hoisting moves variable declarations to the top, event loop manages asynchronous operations, Reactjs and Redux are popular libraries for building user interfaces.

• JS works by interpreting and executing code line by line.

• Hoisting in JS moves variable declarations to the top.

• Event Loop in JS manages asynchronous operations.

• Reactjs and Redux are popular libraries for building user interfaces.

There are two types of exceptions: checked and unchecked.

• Checked exceptions are checked at compile-time and must be handled by the programmer.

• Unchecked exceptions are not checked at compile-time and can be handled by the JVM.

• Examples of checked exceptions include IOException and SQLException.

• Examples of unchecked exceptions include NullPointerException and ArrayIndexOutOfBoundsException.

Use Comparator interface to sort objects by fields in Java.

• Implement Comparator interface and override compare method

• Use Collections.sort() method with custom Comparator

• Example: Sorting a list of Person objects by age field

Optimizing an application involves identifying and resolving performance bottlenecks to improve efficiency and user experience.

• Identify and address slow database queries or inefficient code

• Implement caching mechanisms to reduce load times

• Optimize images and assets to reduce file sizes

• Utilize asynchronous processing to improve responsiveness

• Profile and analyze code to identify areas for improvement

Inner join returns only the rows that have matching values in both tables, while left/right/full outer join returns all rows from one table and matching rows from the other table.

• Inner join: returns rows with matching values in both tables

• Left join: returns all rows from the left table and matching rows from the right table

• Right join: returns all rows from the right table and matching rows from the left table

• Full outer join: returns all rows when there is a match in either ta...read more

Implementing Spring security involves configuring security settings in the Spring application.

• Add Spring Security dependency in pom.xml

• Configure security settings in SecurityConfig class

• Define user roles and permissions

• Use annotations like @EnableWebSecurity and @Secured

Software Development Life Cycle is a process followed by software developers to design, develop and maintain software.

• SDLC consists of several phases including planning, analysis, design, implementation, testing, deployment, and maintenance.

• Each phase has its own set of activities and deliverables.

• The goal of SDLC is to ensure that the software meets the requirements of the stakeholders and is delivered on time and within budget.

• SDLC models include Waterfall, Agile, and DevOp...read more

LinkedList and ArrayList are both implementations of the List interface in Java. LinkedList uses pointers to connect elements, while ArrayList uses a dynamic array to store elements.

• LinkedList uses pointers to connect elements, allowing for efficient insertion and deletion operations.

• ArrayList uses a dynamic array to store elements, providing fast random access to elements.

• LinkedList is better suited for frequent insertions and deletions, while ArrayList is better for frequen...read more

Railway Reservation System for booking train tickets.

• Users can search for trains based on source and destination stations.

• Users can select preferred train, class, and seat.

• System should handle payment processing and generate e-tickets.

• Admin panel for managing trains, schedules, and bookings.

• Integration with SMS/email notifications for updates.

• Database to store train details, user information, and booking history.

Spring MVC is a framework used for building web applications in Java.

• Spring MVC stands for Model-View-Controller, which is a design pattern for separating concerns in a web application.

• It provides a powerful model for building flexible and loosely coupled web applications.

• It integrates with other Spring frameworks like Spring Boot, Spring Security, and Spring Data.

• It uses annotations to simplify configuration and reduce boilerplate code.

• Example: @Controller annotation is used...read more

Design an ETL system for loading structured data

• Identify data sources and destinations

• Create data extraction processes

• Transform data to match destination schema

• Load transformed data into destination

Singleton pattern ensures a class has only one instance, while ConcurrentHashMap allows multiple threads to access and modify a map concurrently.

• Singleton pattern involves creating a class with a private constructor and a static method to return the instance.

• ConcurrentHashMap is a thread-safe implementation of the Map interface, allowing multiple threads to access and modify the map concurrently.

• To implement a singleton pattern, use a private static instance variable and a st...read more

In LWC, == is used for loose equality comparison while ==== is used for strict equality comparison.

• == is used for comparing values without considering data types

• === is used for comparing values while also considering data types

• Example: '1' == 1 will return true, but '1' === 1 will return false

Context API is a feature in React that allows sharing data between components without having to pass props through every level of the component tree.

• Context API provides a way to pass data through the component tree without having to pass props down manually at every level.

• It is particularly useful for passing down global data like themes, user authentication, or language preferences.

• Context API consists of three main parts: the Provider, the Consumer, and the useContext hook...read more

Test suite for a login form

• Test for valid username and password

• Test for invalid username and password

• Test for empty username or password field

• Test for special characters in username or password

• Test for maximum character limit in username and password fields

COND parameter is used in JCL to specify a condition for executing a job step.

• COND parameter is used in IF/THEN/ELSE statements to determine the execution of a job step.

• It can be used to check the return code of a previous step or a specific condition.

• COND parameter can have values like ONLY, EVEN, ONLY EVEN, etc.

• It can also be used with the NOT operator to negate the condition.

• COND parameter can be used with job steps, procedures, and in-stream data sets.