2000+ Java Developer Interview Questions and Answers

Packages in Java help organize code, prevent naming conflicts, and provide access control.

• Organize code into logical groups for easier maintenance and readability

• Prevent naming conflicts by using unique package names

• Provide access control by using access modifiers like public, private, protected, and default

• Facilitate reusability by allowing classes to be easily imported and used in other packages

No, I don't have any Java certificate.

• No, I don't possess any Java certification.

• Unfortunately, I haven't obtained any Java certificate.

• Regrettably, I do not hold any Java certification.

Basic Java and Query questions for Java Developer position.

• OOPs concept helps in creating modular, reusable and maintainable code.

• Polymorphism is the ability of an object to take on many forms.

• JVM stands for Java Virtual Machine, which executes Java bytecode.

• Database connection coding in Java involves creating a connection object, setting connection properties, and executing SQL queries.

• JOIN is used to combine rows from two or more tables based on a related column between the...read more

The interview questions cover a range of topics related to Java development, including Java 8 features, data structures, annotations, and database triggers.

• Use Java 8 features like streams and lambda expressions to compare two strings without using comparator or comparable.

• To print non-duplicate elements in an array, use a HashSet to store unique elements and then iterate through the array to check for duplicates.

• Solid principles refer to a set of design principles for object...read more

A Java program using multithreading to print numbers from 1 to 10 in a specific pattern.

• Create three threads and assign them to print numbers in a specific pattern

• Use synchronization to ensure the correct order of printing

• Use a loop to iterate from 1 to 10 and assign the numbers to the threads

• Print the thread name and the assigned number in the desired format

Some standard Java pre-defined functional interfaces include Function, Consumer, Predicate, and Supplier.

• 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 re...read more

Spring Boot offers annotations like @SpringBootApplication, @RestController, @Autowired, @Component, @RequestMapping, etc.

• @SpringBootApplication - Used to mark the main class of a Spring Boot application.

• @RestController - Used to define a class as a controller in a RESTful web service.

• @Autowired - Used for automatic dependency injection.

• @Component - Used to indicate that a class is a Spring component.

• @RequestMapping - Used to map web requests to specific handler methods.

Use CSS to change the background color of a div element.

• Use the 'background-color' property in CSS to specify the color.

• You can use color names, hex codes, RGB values, or HSL values to set the background color.

• Example: div { background-color: blue; }

Memory is allocated when an instance of a class is created.

• Memory is allocated dynamically when an object is instantiated.

• Each instance of a class has its own memory allocation.

• Memory allocation occurs at runtime, not during class creation.

Daemon thread is a low priority thread that runs in the background and provides services to other threads.

• Daemon threads are used for tasks that don't require user interaction or input.

• They are automatically terminated when all non-daemon threads have completed.

• Examples include garbage collection, logging, and monitoring.

• They can be created using setDaemon() method.

• Daemon threads should not be used for tasks that require data consistency or integrity.

• They can help in improvin...read more

Program for different types of books using Inheritance Concept

• Create a Book class as the parent class

• Create Paperbook, E-book, and Audiobook classes as child classes

• Inherit properties and methods from the Book class

• Add unique properties and methods to each child class

• Example: Paperbook class can have a property for number of pages

• Example: E-book class can have a property for file format

Java 8 introduced several new features including lambda expressions, functional interfaces, streams, and the new Date and Time API.

• Lambda expressions: Allow you to treat functionality as a method argument.

• Functional interfaces: Interfaces with a single abstract method, used for lambda expressions.

• Streams: Provide a new abstraction to work with sequences of elements.

• Date and Time API: Improved API for handling date and time operations.

Local, static, and instance variables differ in their scope and lifetime.

• Local variables are declared inside a method and have a limited scope.

• Static variables belong to the class and are shared among all instances.

• Instance variables are unique to each object and can be accessed using the object reference.

To make a class immutable, use final keyword, make all fields private, provide no setter methods, and ensure deep copy of mutable fields.

• Use final keyword to prevent subclassing

• Make all fields private to restrict direct access

• Provide no setter methods to prevent modification

• Ensure deep copy of mutable fields to avoid sharing references

Synchronized Collection is thread-safe but may have performance issues, while Concurrent Collection is optimized for concurrent access.

• Synchronized Collection uses synchronized keyword to achieve thread-safety, while Concurrent Collection uses non-blocking algorithms like CAS (Compare and Swap).

• Synchronized Collection locks the entire collection during modification, leading to potential performance bottlenecks, while Concurrent Collection allows multiple threads to access and...read more

Internal partitions of Java Virtual Machine

• Java Virtual Machine has three internal partitions: Heap, Stack, and Method Area

• Heap is used for dynamic memory allocation of objects and arrays

• Stack is used for storing method frames and local variables

• Method Area is used for storing class-level data such as method code and static variables

A View is a complete page while a Partial View is a reusable component in MVC.

• A View represents a complete page in MVC which can include layout, content, and other views.

• A Partial View is a reusable component that can be rendered within a View or another Partial View.

• Partial Views are useful for creating modular and reusable components in MVC applications.

• Example: A View may contain the overall layout of a website, while a Partial View may represent a sidebar or a navigation ...read more

Java Strings are immutable to ensure data integrity and security.

• Immutable strings prevent accidental modification of data.

• String pooling optimizes memory usage by reusing existing strings.

• Immutable strings are thread-safe, simplifying concurrent programming.

• String immutability allows for efficient caching and hashing.

• Immutable strings enable safe sharing of string references.

Threads in Java allow concurrent execution of multiple tasks. They can be created in multiple ways.

• Using the Thread class

• Implementing the Runnable interface

• Using the Executor framework

• Using the Callable interface with ExecutorService

Hashtable is synchronized and does not allow null keys or values, while HashMap is not synchronized and allows null keys and values.

• Hashtable is thread-safe, while HashMap is not.

• Hashtable does not allow null keys or values, while HashMap allows null keys and values.

• Hashtable is slower than HashMap due to synchronization.

• Hashtable is a legacy class, while HashMap is part of the Java Collections Framework.

• Hashtable is recommended to be used in multi-threaded environments, whil...read more

Session interface in Hibernate is used to create, read, update, and delete persistent objects.

• Session interface is used to interact with the database in Hibernate.

• It represents a single-threaded unit of work.

• It provides methods for CRUD operations like save, update, delete, and get.

• Session is created using SessionFactory object.

• Example: Session session = sessionFactory.openSession();

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

• Comparable interface is used to define the natural ordering of objects. It is implemented by the class whose objects are to be compared.

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

• Comparable interface has a single method, compareTo(), which compares the current object with another object.

• Comparator...read more

The public static void main method is the entry point of a Java program.

• The main method is declared with the public access modifier, allowing it to be accessed from anywhere.

• The static keyword allows the main method to be called without creating an instance of the class.

• The void keyword indicates that the main method does not return any value.

• The main method takes an array of strings (args[]) as a parameter, which can be used to pass command-line arguments to the program.

Static is used to define class-level variables and methods, while final is used to define constants that cannot be changed.

• Static variables belong to the class itself, while final variables are constants that cannot be modified.

• Static methods can be called without creating an instance of the class, while final methods cannot be overridden.

• Static keyword is used for memory management, while final keyword is used for defining constants.

• Example: static int count = 0; final doubl...read more

Azure and AWS are two major cloud service providers offering similar services but with some differences in features and pricing.

• AWS is the oldest and most widely used cloud service provider, while Azure is catching up quickly.

• Azure is known for its strong integration with Microsoft products and services, while AWS has a wider range of third-party integrations.

• AWS has a larger global presence with more data centers worldwide compared to Azure.

• Pricing models differ between the ...read more

Session in Java is a way to store information about a user across multiple requests.

• Session is used to maintain stateful information about a user.

• It is created when a user first accesses a web application and remains active until the user logs out or the session times out.

• Session data is stored on the server and can be accessed by multiple requests from the same user.

• It is commonly used for user authentication, shopping carts, and personalization.

• The HttpSession interface in ...read more

Java is an object-oriented programming language. Inheritance is a mechanism to create new classes based on existing ones. OOPs is a programming paradigm. Method is a block of code that performs a specific task.

• Java is a high-level, class-based, and object-oriented programming language.

• Inheritance is a mechanism in which one class acquires the properties and behaviors of another class.

• OOPs is a programming paradigm that focuses on objects and their interactions.

• Method is a blo...read more