20+ Java Software Engineer Interview Questions and Answers

Executor framework is used to manage threads and execute tasks asynchronously.

• Executor framework provides a way to manage threads and execute tasks asynchronously.

• It provides a thread pool and a queue to manage tasks.

• It helps in improving the performance of the application by reducing the overhead of creating and destroying threads.

• It also provides a way to handle exceptions and errors in the tasks.

• Example: Executors.newFixedThreadPool(10) creates a thread pool of 10 threads.

Yes, we can pass values during object creation using constructors.

• Constructors are special methods that are called when an object is created.

• They can take parameters to initialize the object's state.

• Values passed during object creation are used to initialize instance variables.

• Example: public class Person { String name; int age; public Person(String name, int age) { this.name = name; this.age = age; } }

• Example usage: Person person = new Person("John", 30);

Exceptions are errors that occur during program execution. There are two types: checked and unchecked.

• Exceptions are objects that represent errors or exceptional conditions that occur during program execution.

• Checked exceptions are checked at compile time and must be handled or declared in the method signature.

• Unchecked exceptions are not checked at compile time and can be handled or left to propagate up the call stack.

• Examples of exceptions include NullPointerException, Arra...read more

Find the next largest in the right side for every array element.

• Iterate through the array from right to left

• Use a stack to keep track of elements

• Pop elements from stack until a greater element is found

• If no greater element is found, assign -1

OOP concepts in Java with real time examples

• Encapsulation - hiding implementation details of a class. Example: private variables in a class

• Inheritance - creating a new class from an existing class. Example: subclass extending a superclass

• Polymorphism - ability of an object to take many forms. Example: method overloading and overriding

• Abstraction - showing only necessary details to the user. Example: abstract classes and interfaces

Find shortest path in 0,1 matrix from (0,0) to (n-1,n-1)

• Use Breadth First Search (BFS) algorithm to find shortest path

• Create a visited matrix to keep track of visited nodes

• Create a distance matrix to keep track of distance from source node

• Start BFS from (0,0) and keep updating visited and distance matrices

• Return distance value at (n-1,n-1) in distance matrix

A user microservice to retrieve data from h2DB

• Create a REST API endpoint to handle user requests

• Use JDBC to connect to the h2DB and retrieve data

• Implement caching to improve performance

• Ensure proper error handling and logging

• Secure the API with authentication and authorization

Find peak in array in less than O(n) time

• Use binary search to find peak element

• Compare middle element with its neighbors to determine direction

• Repeat search in direction of larger neighbor until peak is found

Spring Boot Starter POM is a parent POM that provides a set of dependencies for Spring Boot applications.

• It includes commonly used dependencies such as Spring Framework, Spring Boot, and Spring Data.

• It simplifies the process of configuring and deploying Spring Boot applications.

• Developers can add additional dependencies to the POM file as needed.

• Examples of Spring Boot Starter POMs include spring-boot-starter-web, spring-boot-starter-data-jpa, and spring-boot-starter-test.

IOC stands for Inversion of Control and DI stands for Dependency Injection.

• IOC is a design pattern that allows the flow of control to be inverted, where the framework controls the flow of the program.

• DI is a technique where the dependencies of an object are injected into it, rather than the object creating them itself.

• IOC and DI are closely related and often used together in software development.

• Spring Framework is a popular example of a framework that uses IOC and DI.

Static keyword is used to create class-level variables and methods.

• Static variables are shared among all instances of a class

• Static methods can be called without creating an instance of the class

• Static blocks are used to initialize static variables

• Static import is used to import static members of a class

To create thread singleton, use double-checked locking or enum.

• Use double-checked locking to ensure only one instance is created

• Alternatively, use enum to create a singleton with thread safety

• Ensure proper synchronization to avoid race conditions

Finding the shortest super common string among an array of strings.

• Create a set of all substrings of the first string

• Iterate through the remaining strings and remove substrings not present in them

• Return the shortest remaining substring

Executor framework provides a way to execute tasks asynchronously using multithreading.

• Executor framework provides a way to manage thread pools and execute tasks asynchronously.

• It uses a pool of threads to execute tasks and provides a way to submit tasks to the pool.

• The tasks are executed in a separate thread, allowing for parallel execution.

• Executor framework provides different types of thread pools like fixed, cached, and scheduled.

• It also provides a way to handle exception...read more

Design patterns are reusable solutions to common software problems.

• Design patterns provide a standard way of solving recurring problems in software development.

• There are three types of design patterns: creational, structural, and behavioral.

• Examples of design patterns include Singleton, Factory, Observer, and Decorator.

• Design patterns can improve code readability, maintainability, and scalability.

Collection framework is a set of classes and interfaces that provide a way to store and manipulate groups of objects.

• Collection framework is part of Java's core libraries.

• It includes interfaces like List, Set, and Map, and their respective implementations like ArrayList, HashSet, and HashMap.

• Collections can be sorted, searched, and filtered using various methods.

• Iterators are used to traverse through collections.

• Collections can also be synchronized for thread safety.

• Example: ...read more

Method overloading is having multiple methods with the same name but different parameters. Method overriding is having a method in child class with the same name and signature as in parent class.

• Method overloading is compile-time polymorphism

• Method overriding is run-time polymorphism

• Method overloading is used to provide different ways of calling the same method

• Method overriding is used to provide a specific implementation of a method in a child class

• Method overloading can hav...read more

Detach and merge are used in Spring to manage the persistence of entities.

• Detach is used to remove an entity from the persistence context.

• Merge is used to update the state of a detached entity and merge it back into the persistence context.

• Both detach and merge are commonly used in Spring Data JPA.

• Example: entityManager.detach(entity); entityManager.merge(entity);

The current CTC (Cost to Company) is the total salary package of an employee including all benefits and allowances.

• CTC includes salary, bonuses, incentives, and other monetary benefits.

• It also includes non-monetary benefits like health insurance, retirement plans, and company-provided facilities.

• CTC is used to calculate the net salary after deducting taxes and other deductions.

• It is an important factor for job seekers to evaluate job offers and negotiate salaries.

• Example: Cur...read more

IOC stands for Inversion of Control. Its components are Dependency Injection and Aspect Oriented Programming.

• Dependency Injection: injecting dependencies into a class instead of creating them within the class

• Aspect Oriented Programming: separating cross-cutting concerns from the main logic of the application

• Examples: Spring Framework, Guice

Scopes in Spring refer to the lifecycle of a bean and its visibility within the application context.

• Spring has four standard scopes: singleton, prototype, request, and session.

• Singleton scope creates only one instance of a bean and is the default scope.

• Prototype scope creates a new instance of a bean every time it is requested.

• Request scope creates a new instance of a bean for each HTTP request.

• Session scope creates a new instance of a bean for each HTTP session.

Spring MVC is a web framework while Spring Boot is an opinionated way of building Spring applications.

• Spring MVC requires more configuration and setup compared to Spring Boot

• Spring Boot provides a pre-configured environment for building Spring applications

• Spring Boot includes an embedded server, making it easier to deploy applications

• Spring MVC is more flexible and customizable compared to Spring Boot

• Both frameworks are built on top of the Spring framework