EPAM Systems Senior Java Developer Interview Questions, Process, and Tips

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

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

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 treeSet = new TreeSet<>();