Java Collections Interview Questions

What are collections in Java interview questions?

Collection in Java is a framework used for storing and manipulating collections of objects.

What are the 4 collection classes in Java?

There are many collections in Java but out of them most used collections are:

1. ArrayList
2. LinkedList
3. HashSet
4. Stack

Can HashMap have duplicate keys?

No, HashMap can’t have duplicate keys. As HashMap is one of the collections in Java, it stores the value in the form of key-value and every key has its own value attached to it. So, as no key can have two value means we can’t have duplicate keys in HashMap.

Why array is not a collection?

The array is not a collection, it is all because of the difference in the functionality between collections and arrays few of which are mentioned below:

• The size of the Array can’t be changed once declared
• Arrays can hold only homogeneous data types elements.
• The array can hold both primitive datatypes and objects whereas in collections it is only able to hold wrapper objects.

Java Collection Framework was introduced in JDK 1.2 which contains all the collection classes and interfaces. Java Collection is a framework that provides a mechanism to store and manipulate the collection of objects. It allows developers to access prepackaged data structures and algorithms for manipulating data. 

Here, we’ve covered the 50+ Java Collections Interview Questions and Answers tailored for both Fresher and experienced professionals, which cover everything from basic to advanced Java collection concepts such as navigation collection, WeakHashMap, streams Lambdas, etc.

Whether you are a fresher or an experienced Java developer, these Java Collections Interview Questions give you all the confidence you need to ace your next Java interview.

We have divided the 50 questions into two parts: Experienced and Freshers. Let’s begin with the questions for Freshers.