Java Collection Interview Questions

If you are looking for a job related to Java Collection, you need to prepare for the 2023 Java Collection Interview Questions. Every interview is indeed different as per the different job profiles. Here, we have prepared the important Java Collection Interview Questions and Answers, which will help you succeed in your interview.

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Java Collection framework is one of the key chapters for learning core java properly. This is because Java Collection holds a lot of interfaces and classes which are under java.util package. All those interfaces and classes have huge utilization in any java based application. This 2023 Java Collection Interview Questions article will present the 10 most important and frequently asked Java Collection interview questions.

Part 1 – Java Collection Interview Questions (Basic)

This first part covers basic Java Collection Interview Questions and Answers.

Q1. Java has introduced a different version in almost the last couple of years. The collection framework is always a highlighted package for Java, so every version of Java always came with some key features, specifically on the Collection framework. Explain what are the new features that came with the collection framework for Java 8 version?

Answer:

Java 8 version already came with some of the key or major changes in Java Collection Framework:

• Stream API for Java: For supporting some of the sequential and parallel processing.
• Introducing the for each method specifically for iterator interface: This is one of the default methods when the developer is going to use an iterator for fetching data from any of the collection interfaces. Java 8 introduced one of Lambda expressions key features because of its arguments; it will be very easy to use on the iterator interface.
• Miscellaneous collection API: Many methods have been introduced in the case of Miscellaneous Collection of the framework. Methods are for Each Remaining, replace all, computer, merge specially introduce an Iterator interface.

Q2. Explain in detail about the Java Collections framework used in Java applications. Provide more details on the exact benefits provided by the collection framework in the Java application.

Answer:

The collection framework is kind of a much-highlighted package from the day java introduce this package. Initially, it was only holding some of the legacy interfaces, like Vector, Hashtable, Stack, and Array, which are obsolete in terms of the longtime journey of java. The java upper version introduces many feature-oriented interfaces and comes with some key roles for any kind of java programming. Implementation and defining the algorithm for those interfaces are really useful for any Java developer at any time of execution. Java Collection has worked with these approaches for long days and came with many concurrent collection classes to ensure thread safety on varieties operations.

The benefits of collection framework are defined below:

• Reduced development efforts by implementing defined collection classes.
• Code quality is always enhanced, including performance.
• Efforts on code maintenance have always been reduced.
• Improve code reusability and maintained proper interoperability.

Q3. Explain the benefits of using the collection framework generic version from starting collection interfaces and classes on the Java 4 version onwards.

Answer:

Java 1.5 came with some critical functionalities specifically in the collection framework, which enhances some of the generic interface’s legacy features. It introduced some of the approaches which actually provided ClassCastException at compilation time. Initially, the same exception came at runtime without any previous definition. But in the case of compilation, it will never be identified. If the developer mentioned one collection interface object type, it would never accept any other reference. If by mistake developers have done the same, then it will throw ClasCastExpection at compilation time.

Q4. There are many interfaces already defined in the case of the collection framework design of the existing java application. Explain some of the popular key interfaces available in the collection framework and explain their utility of using them.

Answer:

Some of the key interfaces are defined below, which are available for the Collection framework:

• Collection: It is one of the root interfaces of the entire collection hierarchy. It was actually holding a group of available objects from the development point of view called Elements. Normally any kind of direct implementation of this Collection interface is not available for the Java platform.
• Set: One of the key collection interfaces extends the Collection interface and does not contain any duplicate elements.
• List: One of the ordered collections extends the Collection interface and accepts duplicate elements, which are key differences between set and list.
• Map: Map is also an interface that holds data with the key-value pair. It never contains any duplicate key values.

Q5. Whether the collection frame can able to extend two very key interfaces in Java core packages, one is cloneable, and another one is Serializable. Explain some details explanation of your answer to the above concern.

Answer:

Cloning and serializing on the collection interface is not possible, as the collection interface can have multiple interfaces. So there are some possibilities of duplicating values or unique values on those specific interfaces. So clone or serialize will not be possible on that. But there have some specific methods defined for some common interfaces which may use their own clone method to do this.

Part 2 – Java Collection Interview Questions (Advanced)

Let us now have a look at the advanced Java Collection Interview Questions and Answers.

Q6. In the Collection Framework, one of the key interfaces very frequently used by the developer is called Map. Unfortunately, but surprisingly, the Map interface does not extend the Collection framework directly. Can you explain the same as why it was not extended?

Answer:

The map interface is one of the key interfaces of the collection framework, but it never extends the Collection interface as Map always maintained data as a key-value pair, which never ensures storing multiple elements, which represents one of the key features of the Collection framework.

Q7. One of the important interfaces which are very frequently used in the collection framework which iterator. Explain when it can be useful and what its exact utility of it is.

Answer:

The iterator is one of the popular interfaces for iterating the data available in any active collection. Every collection has one specific method name iterator, which returns the reference of an Iterator object. Two of the key methods have Next and Next ensuring fetching the last row and using the same.

Q8. Two key interfaces in the collection framework for reading data from the collection and using it are Iterator and Enumerator. Explain in detail the difference between the looping approaches available in the collection framework.

Answer:

Enumeration is one of the key iterating features especially using for legacy classes. This is because it was always much faster than the normal iterator interface. But Iterator is always more secure to use as it ensures the thread safety of the iterated collection object.

Q9. Every interface of the collection framework contains one specific method call add for adding some components value in the interface. But in the case of the Iterator interface, there does not have any kind of add method, can you explain why it is not in there?

Answer:

The iterator interface is mainly used for iterating on the data holding by any active collection. Therefore, it will never add any kind of elements and never provide some guarantee on the order of iteration.

Q10. Explain the difference between two key interfaces of the collection framework, Iterator and ListIterator?

Answer:

Iterator and Listiterator are both used for iterating collection data and help the developer work with multiple collection elements.

• Iterator works with all the collections, but ListIteraot only for the List interface.
• The iterator can ensure only forward traverse, but Listiterator can do both forward and backward traverse as well.

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