EPAM Systems Senior Java Developer Interview Questions and Answers

Use Stream API to find the kth largest element in an array of strings.

• Convert array of strings to Stream

• Sort the Stream in reverse order

• Skip k-1 elements and get the kth element

Use SQL query to find highest salary of employee in each department

• Use GROUP BY clause to group by department

• Use MAX() function to find highest salary in each group

• Join the employee table with department table to get department information

Java 8 introduced features like lambda expressions, functional interfaces, streams, and default methods.

• Lambda expressions allow you to pass functionality as an argument to a method.

• Functional interfaces have a single abstract method and can be used with lambda expressions.

• Streams provide a way to work with sequences of elements and perform aggregate operations.

• Default methods allow interfaces to have method implementa...read more

HashMap in Java 8 uses an array of linked lists to store key-value pairs, with bucketing and resizing for efficient retrieval.

• HashMap internally uses an array of linked lists to store key-value pairs

• Each element in the array is a bucket, and each bucket can have multiple entries

• Hashing is used to determine the index of the array where the key-value pair will be stored

• In case of hash collisions, entries are stored in a ...read more

Code becomes less maintainable and can lead to unexpected behavior.

• Violates the principle of substitutability, leading to unexpected behavior in subclasses.

• May result in code that is harder to understand and maintain.

• Can lead to bugs and errors that are difficult to trace back to the violation of the principle.

• Example: If a subclass overrides a method in a way that changes its behavior significantly, it can break the L...read more

Worked on AWS services like EC2, S3, RDS, Lambda, and more. Familiar with features like scalability, security, and cost-effectiveness.

• Worked on EC2 for scalable computing power

• Utilized S3 for secure and durable storage

• Managed RDS for relational database management

• Implemented Lambda for serverless computing

• Familiar with features like scalability, security, and cost-effectiveness

Encapsulation focuses on hiding the internal state of an object, while abstraction focuses on showing only the necessary details of an object.

• Encapsulation is the concept of bundling the data (attributes) and methods (behaviors) that operate on the data into a single unit (class).

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

• Encapsulation helps in d...read more

equals and hashcode are methods in Java used for comparing objects and generating hash codes respectively. Object class does implement equals method.

• equals method is used to compare two objects for equality. It is overridden in most classes to provide custom comparison logic.

• hashcode method is used to generate a unique integer value for an object. It is used in hash-based collections like HashMap.

• Object class does impl...read more

Time complexities of data structures vary based on operations like insertion, deletion, search, etc.

• Arrays - O(1) for access, O(n) for insertion/deletion

• Linked Lists - O(n) for access, O(1) for insertion/deletion at head/tail

• Stacks - O(1) for push/pop operations

• Queues - O(1) for enqueue/dequeue operations

• Hash Tables - O(1) for average case search/insert/delete

• Binary Trees - O(log n) for search/insert/delete in balanced...read more

D stands for Dependency Inversion Principle in SOLID principles.

• High-level modules should not depend on low-level modules. Both should depend on abstractions.

• Abstractions should not depend on details. Details should depend on abstractions.

• Example: Using interfaces to decouple classes and allow for easier testing and maintenance.

Other principles for best coding practices include DRY, KISS, YAGNI, and design patterns.

• DRY (Don't Repeat Yourself) - Avoid duplicating code by creating reusable functions or classes.

• KISS (Keep It Simple, Stupid) - Write simple and easy-to-understand code rather than overcomplicating it.

• YAGNI (You Aren't Gonna Need It) - Only implement functionality that is needed at the present moment, avoiding unnecessary features.

• D...read more

Tree set is a sorted set implementation based on a binary search tree.

• Tree set stores elements in sorted order using a binary search tree

• It does not allow duplicate elements

• Operations like add, remove, and search have O(log n) time complexity

• Example: TreeSet<String> treeSet = new TreeSet<>();