60+ Java Software Developer Interview Questions and Answers

To convert list to arraylist, use ArrayList constructor. To convert arraylist to list, use List constructor.

• To convert list to arraylist, use ArrayList constructor and pass the list as parameter.

• To convert arraylist to list, use List constructor and pass the arraylist as parameter.

• Example: List list = Arrays.asList("one", "two", "three");

• ArrayList arrayList = new ArrayList<>(list);

• Example: ArrayList arrayList = new ArrayList<>(Arrays.asList("one", "two", "three"));

• List list =...read more

Functional interfaces are interfaces with only one abstract method. They are used for lambda expressions and method references.

• Functional interfaces are used for functional programming in Java.

• They are used for lambda expressions and method references.

• They have only one abstract method.

• Examples of functional interfaces are Runnable, Callable, and Comparator.

• Functional interfaces can be annotated with @FunctionalInterface to ensure they have only one abstract method.

Accessing the same ArrayList object by two threads can cause race conditions and lead to unpredictable outcomes.

• Race conditions can occur when two threads try to modify the same element in the array at the same time.

• Synchronization can be used to prevent race conditions and ensure thread safety.

• Using a concurrent collection like CopyOnWriteArrayList can also prevent race conditions.

• If one thread is only reading from the array and the other is modifying it, then synchronizatio...read more

Yes, we can write procedures in String Data JPA to handle complex databases in Spring Data JPA persistence.

• Use @Procedure annotation to call stored procedures in Spring Data JPA.

• Define the stored procedure in the database and then call it using the @Procedure annotation in the repository interface.

• Handle complex database operations by writing custom queries or using native queries in Spring Data JPA.

Explaining CopyOnWriteArrayList and difference between synchronized and concurrent collections.

• CopyOnWriteArrayList is a thread-safe variant of ArrayList where all mutative operations are implemented by making a new copy of the underlying array.

• Synchronized collections use a single lock to synchronize access to the collection, while concurrent collections use multiple locks to allow concurrent access.

• Concurrent collections are designed to handle high-concurrency scenarios, wh...read more

Java 8 introduced new features like lambda expressions, Stream API, default methods, and more.

• Lambda expressions allow functional programming in Java.

• Stream API provides a way to work with collections in a more functional style.

• Default methods allow interfaces to have method implementations.

• Java 8 also introduced the new Date and Time API, Nashorn JavaScript engine, and more.

• MetaSpace in Java 8 is a replacement for the permanent generation in Java 7, used for storing class me...read more

Interprocess Communication in Microservices architecture is typically achieved through lightweight protocols like HTTP or messaging queues.

• Microservices communicate with each other using RESTful APIs over HTTP.

• Message brokers like Kafka or RabbitMQ are used for asynchronous communication between microservices.

• Service mesh tools like Istio can be used to manage communication between microservices.

• gRPC can be used for high-performance, low-latency communication between microser...read more

Java 8 introduced several enhancements to HashMap including performance improvements and new methods.

• Java 8 introduced the 'compute', 'computeIfAbsent', and 'computeIfPresent' methods for HashMap.

• The 'forEach' method was added to HashMap in Java 8 for iterating over key-value pairs.

• Java 8 also introduced the 'merge' method for combining values in case of duplicate keys.

Race condition occurs when multiple threads try to access and modify the same resource simultaneously, while deadlock occurs when two or more threads are waiting for each other to release resources.

• Race condition is a situation in which the outcome of a program depends on the order of execution of its threads.

• Deadlock is a situation where two or more threads are blocked forever, waiting for each other to release resources.

• Race condition can lead to unpredictable behavior and ...read more

I have implemented try-catch blocks for handling exceptions in my project.

• Used try-catch blocks to catch exceptions and handle them gracefully

• Implemented specific catch blocks for different types of exceptions

• Utilized finally block for cleanup operations after exception handling

Yes, unit testing is essential in my projects to ensure code quality and identify bugs early on.

• Yes, I have experience with unit testing in my projects.

• Unit testing helps in identifying bugs early in the development process.

• It ensures code quality and helps in maintaining code integrity.

• Unit tests also serve as documentation for the codebase.

• Examples: JUnit, Mockito, TestNG.

Streams in Java are a sequence of elements that can be processed in parallel or sequentially.

• Streams are used to perform operations on collections of data in a concise and functional way.

• They can be used to filter, map, reduce, and sort data.

• Streams can be processed in parallel to improve performance.

• Examples of stream methods include filter(), map(), reduce(), and sorted().

SpringBootApplication is a combination of three annotations in Spring Boot.

• SpringBootApplication is a meta-annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations.

• @Configuration annotation indicates that the class is a source of bean definitions.

• @EnableAutoConfiguration annotation enables Spring Boot to automatically configure the application based on the dependencies added to the classpath.

• @ComponentScan annotation tells Spring to sc...read more

The main difference between @EnableMock and @Spy in Junit5 is that @EnableMock creates a mock object while @Spy creates a spy object.

• The @EnableMock annotation is used to create a mock object for a class or interface, allowing you to define its behavior using Mockito.

• The @Spy annotation is used to create a spy object, which is a real object with some mock behavior. It allows you to mock specific methods while calling the real methods of the object.

• Mock objects created with @E...read more

The main difference between @PutMapping and @PatchMapping is the level of data that is updated.

• PutMapping is used to update an entire resource, while PatchMapping is used to update only specific fields of a resource.

• PutMapping replaces the entire resource with the new data provided, while PatchMapping updates only the specified fields.

• PutMapping is idempotent, meaning multiple identical requests will have the same effect as a single request, while PatchMapping may not be idem...read more

ResponseState and ServerState are different states in a software system that represent different aspects of the system's functionality.

• ResponseState typically refers to the state of a response object in a software system, indicating whether the response was successful, failed, or pending.

• ServerState, on the other hand, refers to the state of the server in a software system, indicating whether the server is running, stopped, or experiencing issues.

• ResponseState is more focused...read more

ConcurrentModificationException is thrown when an object is modified concurrently while iterating over it.

• Occurs when a collection is modified while being iterated over using an iterator

• Can be avoided by using ConcurrentHashMap or CopyOnWriteArrayList

• Example: ArrayList being modified while iterating over it

Polymorphism is the ability of a single function or method to operate on different data types. Types include compile-time and runtime polymorphism.

• Polymorphism allows a single function to work with different data types.

• Compile-time polymorphism is achieved through method overloading.

• Runtime polymorphism is achieved through method overriding.

• Example: Overloading a method with different parameter types.

• Example: Overriding a method in a subclass to provide specific implementatio...read more

SQL stands for Structured Query Language. DDL commands are used to define the structure of a database. RDBS stands for Relational Database Management System.

• SQL stands for Structured Query Language

• DDL commands are used to define the structure of a database

• RDBS stands for Relational Database Management System

Yes, RESTful web services use HTTP methods to implement the concept of REST.

• HTTP methods like GET, POST, PUT, DELETE are used to perform CRUD operations on resources.

• GET is used to retrieve a resource, POST is used to create a new resource, PUT is used to update an existing resource, and DELETE is used to delete a resource.

• RESTful web services use these HTTP methods to provide a uniform interface for accessing and manipulating resources.

• For example, a RESTful web service for ...read more

The Java program counts the length of a string without using foreach and length function.

• Iterate through each character of the string using a for loop

• Increment a counter variable for each character encountered

• Return the counter variable as the length of the string

Program to find largest number in array with increasing then decreasing numbers.

• Find the peak element in the array using binary search.

• If peak element is at index 0 or last index, return it.

• Else, search for largest element in left and right subarrays.

Run time polymorphism is method overriding while compile time polymorphism is method overloading.

• Compile time polymorphism is resolved at compile time while run time polymorphism is resolved at runtime.

• Method overloading is an example of compile time polymorphism while method overriding is an example of run time polymorphism.

• Compile time polymorphism is faster than run time polymorphism as it is resolved at compile time.

• Run time polymorphism is achieved through inheritance an...read more

HashMap is a data structure that stores key-value pairs and uses hashcode and equals methods for efficient retrieval.

• HashMap uses hashcode to generate an index for the key-value pair

• If two keys have the same hashcode, equals method is used to check for equality

• If equals method returns true, the value associated with the key is returned

• If equals method returns false, a collision occurs and the key-value pair is stored in a linked list at the index

Printing odd and even numbers in sequence using threads.

• Create two threads, one for odd and one for even numbers.

• Use a shared variable to keep track of the current number.

• Use synchronized block to ensure only one thread is executing at a time.

• Use wait() and notify() methods to signal the other thread.

• Terminate the threads when the desired number of iterations is reached.

Abstract class can have both abstract and non-abstract methods, while interface can only have abstract methods.

• Abstract class can have constructor, fields, and methods, while interface cannot have any of these.

• A class can implement multiple interfaces but can only extend one abstract class.

• Abstract classes are used to provide a common base for subclasses, while interfaces are used to define a contract for classes to implement.

• Example: Abstract class - Animal with abstract met...read more

SQL query to find the 2nd highest salary of an employee.

• Use the SELECT statement to retrieve the salaries in descending order.

• Use the LIMIT clause to limit the result to the second row.

• Use the OFFSET clause to skip the first row.

• Combine the above steps in a single SQL query.

Securing REST API's involves using authentication, authorization, encryption, and input validation.

• Use authentication mechanisms like OAuth, JWT, or API keys to verify the identity of clients accessing the API.

• Implement authorization to control what actions different users can perform on the API.

• Encrypt data transmission using HTTPS to prevent eavesdropping and man-in-the-middle attacks.

• Validate and sanitize input data to prevent injection attacks like SQL injection or cross-...read more

A contractor is a person or company hired to perform specific tasks or provide services for a limited period of time.

• Contractors are typically hired on a project basis or for a specific duration.

• They are not considered employees of the company and are responsible for their own taxes and benefits.

• Contractors may work independently or be part of a contracting firm.

• They often have specialized skills or expertise in a particular field.

• Examples of contractors include freelance dev...read more

I am passionate about programming and Java is a versatile language with a wide range of applications.

• Java is widely used in the industry and has a strong community support.

• Java is platform-independent and can be used to develop applications for various devices.

• Java has a rich set of libraries and frameworks that make development faster and easier.

• Java is used in a variety of domains such as web development, mobile app development, and enterprise software development.

• I have ex...read more

Proficient in C language and Java programming with experience in developing software applications.

• Strong understanding of data structures and algorithms in C language

• Experience in developing web applications using Java

• Knowledge of object-oriented programming principles in Java

• Familiarity with Java frameworks like Spring and Hibernate

Java exception handling is a mechanism to handle runtime errors and prevent program termination.

• Exceptions are objects that are thrown at runtime when an error occurs

• try-catch blocks are used to handle exceptions

• finally block is used to execute code regardless of whether an exception is thrown or not

• Exception hierarchy includes checked and unchecked exceptions

• Examples of exceptions include NullPointerException, ArrayIndexOutOfBoundsException, and FileNotFoundException

Arrays store elements in contiguous memory locations, while linked lists store elements in nodes with pointers to the next node.

• Arrays have fixed size, while linked lists can dynamically grow or shrink.

• Accessing elements in arrays is faster (O(1)), while accessing elements in linked lists is slower (O(n)).

• Inserting or deleting elements in arrays can be inefficient as it may require shifting elements, while in linked lists it can be done in constant time (O(1)).

Exception handling in Spring Boot involves using try-catch blocks, global exception handlers, and custom exception classes.

• Use try-catch blocks to handle exceptions within specific methods.

• Implement global exception handlers to handle exceptions across the entire application.

• Create custom exception classes to handle specific types of exceptions.

• Use the @ExceptionHandler annotation to define methods that handle specific exceptions.

• Use the @ControllerAdvice annotation to define...read more

Accenture is a leading global professional services company known for its innovative solutions and diverse opportunities.

• Accenture offers a wide range of projects and clients to work with, providing valuable experience and growth opportunities.

• The company values diversity and inclusion, creating a supportive and collaborative work environment.

• Accenture invests in training and development programs to help employees enhance their skills and advance their careers.

• The company is ...read more

Writing clean and easy-to-understand code involves following best practices and using proper coding conventions.

• Use meaningful variable names and comments to explain complex logic

• Break down large tasks into smaller, manageable functions

• Follow coding standards and conventions like indentation and naming conventions

DML full form is Data Manipulation Language. Range of char is 0 to 65,535.

• DML is used to manipulate data in a database.

• Char is a data type in Java used to store a single character.

• The range of char is from 0 to 65,535, which represents all Unicode characters.

Annotation used in Spring framework to automatically wire dependencies

• Used to inject dependencies into a class without explicitly instantiating them

• Reduces boilerplate code and improves code maintainability

• Can be used on fields, constructors, or setter methods

• Requires the use of Spring's dependency injection container

HashMap is a data structure that stores key-value pairs and provides constant time complexity for basic operations.

• HashMap uses hashing to store and retrieve elements

• It allows null values and only one null key

• Collisions are resolved using separate chaining or open addressing

• The initial capacity and load factor can be specified during initialization

• The size of the HashMap is dynamically increased as elements are added

Object-oriented programming concepts in Java

• Encapsulation: bundling data and methods together

• Inheritance: creating new classes from existing ones

• Polymorphism: using a single interface to represent different types

• Abstraction: hiding implementation details and providing a simplified view

• Encapsulation: grouping related data and methods into objects

Comparable is an interface used for natural ordering, while Comparator is an interface used for custom ordering.

• Comparable is implemented by the class itself to define the natural ordering of objects.

• Comparator is implemented by a separate class to define custom ordering of objects.

• Comparable uses the compareTo() method to compare objects, while Comparator uses the compare() method.

• Example: String class implements Comparable interface for natural ordering, while Collections.s...read more

The == operator is used to compare references in Java, while the .equals() method is used to compare values. Method overloading is when multiple methods have the same name but different parameters.

• Use == to compare references, use .equals() to compare values

• Method overloading allows multiple methods with the same name but different parameters

• Example: String str1 = new String("hello"); String str2 = new String("hello"); str1 == str2 will be false, but str1.equals(str2) will be...read more

HashMap is an implementation of Map interface that stores key-value pairs using a hash table.

• HashMap uses hashing to store and retrieve elements.

• It uses an array of linked lists to handle collisions.

• The hash code of the key is used to determine the index of the array.

• If multiple keys have the same hash code, they are stored in the same linked list.

• When retrieving a value, the hash code is used to find the correct linked list and then linearly search for the key.

Singleton design pattern ensures a class has only one instance and provides a global point of access to it.

• Create a private static instance of the class

• Provide a public static method to access the instance

• Ensure the constructor is private to prevent instantiation

To avoid hash collisions, use a good hash function, increase the size of the hash table, and handle collisions using techniques like chaining or open addressing.

• Use a good hash function that distributes the keys evenly across the hash table.

• Increase the size of the hash table to reduce the chances of collisions.

• Handle collisions using techniques like chaining (using linked lists) or open addressing (probing).

• Chaining example: Store multiple values with the same hash key in a ...read more

Method overloading is the ability to have multiple methods with the same name but different parameters.

• Method overloading allows a class to have multiple methods with the same name but different parameter lists.

• The methods must have different parameter types or different number of parameters.

• The compiler determines which method to call based on the arguments passed during the method invocation.

Static keyword is used to create class-level variables and methods that can be accessed without creating an instance of the class.

• Static variables and methods belong to the class, not the instance

• Static variables are initialized only once, at the start of the program

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

• Static methods cannot access non-static variables or methods