If you’re preparing for coding interviews or just sharpening your Java skills, solving real-world coding problems is one of the best ways to improve. From string manipulation to multi-threading challenges, these Java coding questions will help you think like a problem-solver and write efficient code.
Below, I’ve grouped some of the most popular Java coding challenges into categories to make your learning journey easier.
🔰 Beginner-Friendly Java Programs
- Find duplicate words in a string.
- Swap two strings without using a temporary variable.
- Move all zeroes to the end of an array.
- The classic FizzBuzz problem.
- Convert decimal numbers into Binary, Octal, and Hexadecimal formats.
✨ String Manipulation & Algorithms
- Print all permutations of a string (recursion & backtracking).
- Reverse a string while preserving spaces.
- Find the longest substring without repeating characters.
- Check if two strings are rotations of each other.
- Find the longest palindrome in a given string.
📊 Array & Data Structure Challenges
- Find the missing number in an array.
- Find the top two maximum numbers.
- Print all pairs with a given sum.
- Identify leaders in an array.
- Rearrange array elements in alternating positive & negative order.
- Find the maximum subarray sum (Kadane’s Algorithm).
- Find intersection of two sorted arrays.
⚡ Multi-threading & Concurrency
- Print odd and even numbers using two threads.
- Create and detect a deadlock in Java.
- Best practices to avoid deadlocks.
- Solve the Producer-Consumer problem using
wait()andnotify().
🌳 Linked List & Binary Tree Problems
- Reverse a singly linked list.
- Find the middle node of a linked list in one pass.
- Detect if a linked list has a cycle.
- Check if a linked list is a palindrome.
- Implement Binary Search Tree (BST) insert, traverse, and delete.
- Find the Lowest Common Ancestor (LCA) in a binary tree.
📂 File Handling & Utilities
- Count characters, words, and lines in a file.
- Sort the contents of a text file.
- Find the most repeated word in a file.
- Append new text to an existing file.
🎯 Perfect for Interviews
Many of these questions are commonly asked in interviews at top tech companies. Practicing them will help you:
✅ Strengthen your Java fundamentals
✅ Think in terms of algorithms & efficiency
✅ Build confidence before your next coding round
📥 Download the Full List (With Code Solutions)
This Document only scratches the surface. The complete PDF (40+ pages) contains detailed explanations and working code for all these problems.
👉 Download Full Java Coding Questions & Answers PDF
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