Virinchi Technologies Java Developer Interview Questions and Answers

Custom stack with constant time access to minimum element

• Use two stacks - one to store elements and another to store minimum values

• When pushing an element, compare with top of min stack and push the smaller value

• When popping an element, pop from both stacks

• Access minimum element in O(1) time by peeking at top of min stack

To create an immutable class named Employee with fields for name and hobbies defined as List<String>, use private final fields and return new instances in getters.

• Use private final fields for name and hobbies in the Employee class

• Provide a constructor to initialize the fields

• Return new instances or unmodifiable lists in the getters to ensure immutability

Add hashCode() and equals() methods to Employee class.

• Override hashCode() method to generate a unique hash code for each Employee object.

• Override equals() method to compare Employee objects based on their attributes.

• Ensure that the attributes used in hashCode() and equals() methods are immutable.

• Example: Add id, name, and department attributes to Employee class and override hashCode() and equals() methods based on thes

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 within the class itself.

• Provide a public static method to access the instance, creating it if necessary.

• Ensure the constructor of the class is private to prevent instantiation from outside the class.

• Use lazy initialization to create the instance only when needed.

• Thread...read more

Ways to create a thread in Java include extending the Thread class, implementing the Runnable interface, and using Java 8's lambda expressions.

• Extend the Thread class and override the run() method

• Implement the Runnable interface and pass it to a Thread object

• Use Java 8's lambda expressions with the Executor framework

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

• Single Responsibility Principle (SRP) - A class should have only one reason to change. Example: A class that handles user authentication should not also handle database operations.

• Open/Closed Principle (OCP) - Software entities should be open for extension but closed for modific...read more

OOP is a programming paradigm based on the concept of objects, which can contain data in the form of fields and code in the form of procedures.

• OOP focuses on creating objects that interact with each other to solve a problem.

• Encapsulation is a key concept in OOP, where data is kept within an object and only accessible through its methods.

• Inheritance allows objects to inherit attributes and methods from parent classes.

• Po...read more

Threads communicate in Java through shared memory or message passing.

• Threads can communicate through shared variables in memory.

• Threads can communicate through synchronized methods or blocks.

• Threads can communicate through wait(), notify(), and notifyAll() methods.

• Threads can communicate through message passing using classes like BlockingQueue or ExecutorService.

Program to reverse a linked list

• Create a new linked list to store the reversed elements

• Traverse the original linked list and insert each node at the beginning of the new list

• Update the head of the new list as the last node of the original list

String literals are constant strings defined in code, while the string pool is a memory area where unique string objects are stored.

• String literals are created using double quotes, while string pool objects are created using the 'new' keyword.

• String literals are stored in the string pool to conserve memory and improve performance.

• String literals are automatically interned by the JVM, while string pool objects need to b

Program to print the 90-degree rotated view of a 2D array.

• Iterate through each column in reverse order and print the corresponding row elements.

• Repeat this process for all columns to get the rotated view of the 2D array.