Java Play interview Questions & Answers (2025)

Play Framework makes it easy to build scalable, fast and real-time web applications with Java and Scala. In other words, Play Framework is a core offering of the Typesafe Reactive Platform. It is a web app framework, written in Scala and Java that provides iterative and Reactive application development very simple. The Play is a clean alternative to the legacy Enterprise Java stacks.

Collections are utilized in various programming languages and basic release contained some classes for collections such as Vector, Stack, Hashtable, and Array. But the more scope and uses Java 1.2 came up with collections Framework the collections interfaces, implementations and different type algorithms.

Some of the advantages of collections framework are:

• The reduce development effort by using core collection classes rather than defining collection classes.
• The code quality is improved with the use of completely tested collections framework classes.
• Reduce some effort for code maintenance by utilizing collection classes with the JDK.
• Collection framework also provides reusability and Interoperability.

The Java 1.5 came with Generic and more collection interfaces and implementations use it mostly. The Generics provide us the type of object that a collection can obtain, so if you try to understand and add any element of a different type it throws compile time error.

There are four main basic interfaces of Java Collections Framework:

• Collection: The collection defines is the root of the collection hierarchy. A collection provides a group of different objects called its element.
• Set: Set is a collection which cannot provide duplicate elements. Set interface models the mathematical set abstraction and it is used for a deck of cards.
• List: A list provides ordered and collection can obtain duplicate elements. So, you can easily find any element from its indexes.
• Map: A map cannot obtain duplicate keys. Each key can map to at most one value.

The some different type’s interfaces are:

• Queue
• Dequeue
• Iterator
• SortedSet
• SortedMap
• ListIterator

The iterator interface provides a different technique to iterate over any Collection. So we can easily get iterator instance from a collection utilizing iterator technique. The iterator takes the place of Enumeration in the Java Collection Framework. The iterator also provides the caller to destroy elements from the underlying collection at the time of the iteration.

An Enumeration is twice as fast as Iterator and it is used for very less memory. Enumeration also is used for is very basic and fits to basic needs.   But the Iterator is safer as compared to Enumeration because it always denies different threads to modify the group object is being iterated by it. The Iterator provides the caller to destroy elements from the underlying that is not possible with Enumeration.

Here are some of the most important advantages:

• Modern stacks
• Java and (Scala)
• Amazing error handling
• Reactive
• Open
• Supported
• Flexible
• Graphically improved developer productivity

The Iterator fail-fast property test for any modification in the structure of the underlying collection every time we try to get the next element. If there are any modifications found, by CocurrentModificationException. The complete implementations of Iterator in Collection classes fail-fast by make except for the concurrent collection classes such as ConcurrentHashMap and CopyOnWriteArrayList.

The UnsupportedOperationException is the exception; it is used for indicating that the operation is not supported. It is also used extensively in JDK classes, in Collection Framework, java.util.collections.UnmodifiableCollection by this exception for all add or remove operations.