Top 25 Java Collections Interview Questions for Wipro and Capgemini — With Answers (2025)

Wipro and Capgemini interviews often follow a pattern: after basic Java questions they go deep into Collections — how they work, when to use which one, and why. This post collects the 25 most-asked Collections questions with short, clear answers and code examples. Read this the night before your interview and you’ll walk in confident. Table of Contents 1. What is the Java Collections Framework? 2. What is the difference between Collection and Collections? 3. What is the difference between ArrayList and LinkedList? 4. What is the difference between ArrayList and Vector? 5. What is the difference between HashSet, LinkedHashSet and TreeSet? 6. What is the difference between HashMap and Hashtable? 7. What is the difference between HashMap and LinkedHashMap? 8. How does HashMap work internally? 9. What is the difference between HashMap and TreeMap? 10. What is the difference between Iterator and ListIterator? 11. What is ConcurrentModificationException and how do you avoid it? 12. What is t