Java Interview Programming Questions for 8+ Years Experienced Developers

Scope

This guide consolidates commonly reported Java programming questions from interview experiences shared on Glassdoor and similar platforms, focusing on candidates with around 8 years of experience.

Common String Problems

Frequently asked problems include:

Reverse each word in a sentence
Find character frequency using HashMap
Check whether two strings are anagrams
Longest substring without repeating characters
First non-repeating character
String and number palindrome
Generate all permutations of a string
String compression (aabcc -> a2b1c2)
Convert a string to an integer without Integer.parseInt()

Reported examples include reversing words in a sentence and character frequency counting.

Number-Based Problems

Common questions:

Armstrong number
Prime number (optimized)
Fibonacci (iterative, recursive, DP)
Factorial
Fast exponentiation
Palindrome number
Count digits / sum of digits
Missing number in an array

Array Problems

High-priority topics:

Two Sum / Three Sum
Find duplicates without extra space
Longest consecutive sequence
Kadane’s Algorithm
Rotate array
Merge sorted arrays
Kth largest element
Stock buy/sell
Subarray with given sum

HashMap and Collections

Senior-level collection problems include:

Character frequency
LRU Cache
Custom HashMap
First duplicate
Group anagrams
Sort map by values
Cycle detection

Linked List

Typical questions:

Reverse linked list
Detect cycle (Floyd’s algorithm)
Merge sorted lists
Find middle node
Remove Nth node from end
Clone linked list with random pointer

Stack and Queue

Valid parentheses
Min Stack
Queue using stacks
Next greater element
Sliding window maximum

Multithreading and Concurrency

Very common for experienced developers:

Print odd/even using two threads
Producer-Consumer
Thread-safe Singleton
Deadlock creation and resolution
Custom blocking queue

flowchart LR
    A[Producer] -->|enqueue| B[Blocking Queue]
    B -->|dequeue| C[Consumer]

Interviewers often ask follow-up questions about synchronization, memory visibility, locking, and scalability.

Java 8+ Functional Programming

Expected Stream API exercises:

Find duplicates
Group by property
Frequency counting
Object sorting
Convert list to map
Flatten nested collections

Design-Oriented Coding

Senior candidates are commonly asked to implement:

LRU Cache
Rate Limiter
Parking Lot
Thread Pool
In-memory Cache

Pattern and Matrix Problems

Star patterns
Spiral matrix
Rotate matrix
Search in sorted matrix

Company-Specific Examples

Company	Reported Coding Topics
Oracle	Closest palindrome
JPMorgan	Concurrency, locking
Publicis Sapient	Longest consecutive sequence
Amdocs/Cognizant	Core Java + coding exercise

What Changes for 8+ Years

Senior interviews typically emphasize:

Time and space optimization
Clean, maintainable code
Concurrency correctness
Practical backend design

Typical interview structure:

flowchart TD
    A[Coding Round] --> B[Solution Discussion]
    B --> C[Optimization]
    C --> D[Concurrency Follow-up]
    D --> E[System Design Discussion]

Common follow-up questions:

Make it thread-safe.
Reduce memory usage.
Handle millions of requests.
Improve time complexity.

Key Takeaways

Senior Java interviews focus on optimization, concurrency, and practical design in addition to coding.
Arrays, collections, multithreading, and Java Streams are consistently emphasized.
Expect follow-up discussions around scalability, thread safety, and production-quality implementation.
Preparing the top 20 problems provides strong coverage for many backend Java interviews.