Introduction to Java Collections Interview Questions And Answers
Java Collection framework is one of the key chapters for learning core java properly. 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.
Now, if you are looking for a job which is related to Java Collections then you need to prepare for the 2019 Java Collections Interview Questions. It is true that every interview is different as per the different job profiles. Here, we have prepared the important Java Collections Interview Questions and Answers which will help you get success in your interview.
In this 2019 Java Collections Interview Questions article, we shall present 10 most important and frequently used Java Collections interview questions. These interview questions are divided into two parts are as follows:
Part 1 – Java Collections Interview Questions (Basic)
This first part covers basic Java Collections Interview Questions and Answers.
Q1. Java has introduced a different version in almost last couple of years. 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. Please explain what are the new features came with a collection framework for Java 8 version?
Java 8 version already came with some of the key or major changes in Java Collection Framework, features are explaining below:
- Stream API for Java: For supporting some of the sequential and parallel processing.
- Introducing for Each method specifically for iterator interface: This is one of the default methods when the developer is going to use iterator for fetching data from any of the collection interface. Java 8 introduced one of the key features called Lambda expressions because of its arguments, it will be very easy to use on the iterator interface.
- Miscellaneous Collection API: A lot of methods have been introduced in case of Miscellaneous Collection of the framework. Methods are for Each Remaining, replace all, computer, merge specially introduce in Iterator interface.
Q2. Explain in details about the Java Collection framework using in Java application. Provide more details on exact benefits provided by collection framework in Java application?
Collection framework is kind of a much-highlighted package from the day java introduce this package. Initially, it only holding some of the legacy interfaces, like Vector, Hash table, Stack, and Array, which are obsolete in terms of a longtime journey of java. From java upper version introducing a lot of interfaces which very much feature-oriented and come with some key role for any kind of java programming. Implementation can define the algorithm for those interfaces are really useful for any Java developer any time of execution. Java Collection has worked with these approaches long days and came with a lot of concurrent collection class for ensuring thread safety on varieties operations.
Benefits of collection framework defined below:
- Reduced development efforts by implementing defined collection classes.
- Code quality is always enhanced including performance.
- Efforts on code maintenance always been reduced.
- Improve code responsibility and maintained proper interpretability.
Let us move to the next Java Collections Interview Questions.
Q3. Explain details benefits available in case of using collection framework generic version from the starting of collection interfaces and classes on Java 4 version onwards?
Java 1.5 came with some critical functionalities on specifically in collection framework, which enhances some of the generic interfaces legacy features. It introduced some of the approaches which actually provided Class Cast Exception at compilation time. Initially, the same exception came at run-time without any previous definition. But in the case of compilation, it will never be identified. Now if developer mentioned one collection interface object type, then it will never able to accept any other object reference. If by mistake developer have done the same, then it will throw Class Cast Exception at compilation time.
Q4. There have a lot of interfaces already defined in case of collection framework design of existing java application. Please explain in details about some of the popular key interfaces available in collection framework, explain their utility of using?
This is the common Java Collections Interview Questions asked in an interview. Some of the key interfaces are defined below which are available for Collection framework:
- Collection: It is one of the root interfaces of the entire collection hierarchy. It actually holds a group of available objects which from a development point of view called Elements. Normally any kind of direct implementation of this Collection interface is not available for the Java platform.
- Set: This is one of the key collection interfaces which extend Collection interface and ensure of not containing any duplicate elements.
- List: It is one of the ordered collection which extending Collection interface and accepting duplicate elements, which are one of the key difference between set and list.
- Map: Map is also an interface which holding data with a key-value pair. It never contains any duplicate key values.
Q5. Whether a collection frame can able to extend two very key interfaces in Java core packages, one is cloneable and another one is Serializable? Please explain some details explanation of your answer to the above concern?
Cloning and serializing on collection interface is not possible at all, as collection interface can have multiple interfaces and there have some possibilities of getting duplicate values or unique values on those specific interfaces. So clone or serialize will not possible on that. But there has some specific method defined for some common interface which may use own clone method to do this.
Part 2 –Java Collections Interview Questions (Advanced)
Let us now have a look at the advanced java Collections Interview Questions and Answers.
Q6. In Collection Framework, one of the key interface very frequently used by the developer called Map. But surprisingly Map interface not extend Collection framework directly. Can you please explain the same why it not extended?
The map interface is one of the key interfaces of collection framework, but it never extends Collection interface as Map always maintained data as a key-value pair, which never ensure of storing multiple elements, which represents one of the key features of Collection framework.
Q7. One of the important interface which is very frequently used in collection framework which iterator. Please explain when it can be used and what the exact utility of it is?
An 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 a reference of an Iterator object. Then two of the key methods has Next and Next ensuring of fetching the last row and using the same.
Let us move to the next Java Collections Interview Questions.
Q8. Two key interfaces in collection framework for reading data from the collection and using it are Iterator and Enumerator. Please explain in details what can be the difference in between both the looping approaches available in collection framework?
Enumeration is one the key iterating feature especially using for legacy classes. It always much faster than a normal iterator interface. But Iterator is always more secure to use as it ensuring thread safety of the iterated collection object.
Q9. Every interface of collection framework contains one specific method call add for adding some components value in the interface. But in the case of Iterator interface there does not have any kind of add method, can you explain why it not in there?
This is the most popular Java Collections Interview Questions asked in an interview. Iterator interface mainly used for iterating on the data holding by any active collection. It will never add any kind of elements and never able to provide some guaranty on the order of iteration.
Q10. Explain the difference between two key interfaces of the collection framework, Iterator, and ListIterator?
Iterator and Listiterator both are using for iterating collection data and help the developer for working with multiple elements of a collection. Difference between them is explained in below:
- Iterator working with all the collection, but ListIteraot only for List interface.
- The iterator can ensure only forward traverse but Listiterator can do both forward and backward traverse as well.
This has been a guide to the list of Java Collections Interview Questions and Answers so that the candidate can crackdown these Java Collections Interview Questions easily. Here in this post, we have studied top Java Collections Interview Questions which are often asked in interviews. You may also look at the following articles to learn more –