Java Collection Interview Questions

Get Prepared for Your Next Tech Interview with These FAs


A collection is a framework that provides a way to store & manipulate a group of objects. It includes interfaces like Collection & Map, & classes like ArrayList, HashSet, etc.

What is Collection in Java?

1. Explain various interfaces used in Collection framework.  2. Differentiate between HashSet & TreeSet. When would you prefer TreeSet to HashSet?

Java Collection Interview Questions for Freshers

3. What is the default size of the load factor in the hashing-based collection?  4. How can you make an ArrayList read-only in Java?

5. Differentiate between HashSet and HashMap.  6. Explain the hierarchy of the Collection framework in Java.

1. Differentiate between Comparable & Comparator in the context of Java.  2. Explain fail-fast & fail-safe iterators. 

Java Collection Interview Questions for Experienced

3. What is the use of Properties class in Java? Explain its pros. 4. Why does HashMap allow null whereas HashTable does not allow null?

5. Why do we need synchronized ArrayList when we have Vectors (synchronized) in Java?  6. Why Map interface doesn't extend Collection Interface or vice-versa?

1. Write a program in Java to display the contents of a HashTable using enumeration. 2. Write a program in Java to clone a Treeset to another Treeset.

Java Collection Programs

3. Write a program in java to join two ArrayList into one ArrayList.  4. Given an array in Java, convert it to a collection.

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