Top 15 Java-8 Interview Questions (2023)

Java is undeniably one of the first names that come to our mind when we talk about software development. A primary driving power behind the global digital lifestyle, Java is an object-oriented programming (OOP) language developed by James A. Gosling in the mid-1990s, together with Patrick Naughton and Mike Sheridan. 

With its many perks that include platform independence, object-oriented nature, and ease of learning, Java finds a host of applications in the software industry; be it Android applications, web-based applications, or desktop GUI applications, computers without Java are legit unimaginable. 

The latest addition to the incredible functionalities of Java is Java 8, an open-source project released on March 18, 2014. Regarded as a revolutionary release for software development platforms, Java 8 is packed with upgrades and new features to the Java programming, tools, libraries, and JVM. The Oracle Corporation currently manages it.

Needless to say, Java 8 interview questions are a hot topic in the field of software development. Moreover, if you are a fresher looking to make it big as a software developer or a related job title, let us walk you through the top Java 8 interview questions and answers you should go through as part of your D-day prep. In addition, we will talk about some popular upGrad courses that will help you get a step closer to your dream job!

Top 15 Java 8 Interview Questions and Answers

1. What are the new features added to Java 8?

The essential features included in Java 8 include:

• Functional interfaces
• Lambda expression
• Method references
• Stream API
• Date time API
• Optional
• Default method
• Nashorn, JavaScript Engine

2. What are functional interfaces?

Functional interfaces are interfaces that have only one abstract method. These interfaces are implemented using a Lambda expression. Thus, to use a Lambda expression, we need to create a new functional interface or use the predefined one of Java 8.

3. What are the characteristics of the Lambda function?

Main characteristics of the Lambda function include:

• A method defined as Lambda expression can be passed as a parameter to a different method.
• There is no requirement of declaring the parameter type since the compiler can fetch the same from the parameter’s value.
• A method can exist independently without belonging to a class.
• Using a single parameter does not require parentheses, but the same can be done using multiple parameters.
• There is no need to use curly braces if the body of expression has only a single statement.

4. What is the structure of the Lambda expression?

Lambda expression has the following structure:

(Argument List) ->{statements;} or

(Argument List) ->{expression;}

5. What are method references?

Method references in Java 8 are a particular type of Lambda expression used for creating simple Lambda expressions by referencing existing methods. The different kinds of method references are – reference to a static method, reference to a constructor, and reference to an instance method.

6. What are Default Methods in Java 8?

Default methods are those methods of the interface which have a body and utilize default keywords. Default methods have the property of backward compatibility. It means that if we add the default method in an interface, we will be able to provide the default implementation without affecting the implementing classes. However, if JDK modifies any interface that does not have the default method, then the classes that implement the said interface will break.

7. What is an optional class?

Optional classes are special wrapper classes in Java 8 for avoiding NullPointerExceptions. NullPointerExceptions occur when we fail to perform Null checks. Optional classes encapsulate optional value that is either present or not.

8. Give some examples of standard Java pre-defined functional interfaces?

The functional interfaces introduced by Java 8 include Predicate, Consumer, Supplier, etc. But popular pre-defined functional interfaces from earlier Java versions include the following:

• Runnable: For executing the instances of a class over another thread with no return value and no arguments.
• Comparable: For sorting objects in the natural sort order.
• Comparator: For sorting different objects as per user-defined order.
• Callable: For executing the instances of a class over another thread with no arguments. It either throws an exception or returns a value.

9. Name the various categories of pre-defined functional interfaces and their uses.

The various categories of pre-defined functional interfaces are:

• Function: For transforming arguments in returnable value.
• Operator: For performing reduction type operations that accept the same input types.
• Consumer: Accepts arguments but does not return any values.
• Supplier: Returns a value but does not accept any arguments.
• Predicate: For performing a test and returning a boolean value.

10. What are some date and time APIs in Java 8?

LocalTime, LocalDate, and LocalDateTime are the core date and time API classes in Java 8. These classes are local to the context of the observer and denote the current time and date in the context of the observer.

11. What were the drawbacks of the old date and time?

The old date and time suffered from the following limitations:

• Java 8 time and date API meet the ISO standards, but the old date and time had a poor design.
• While the latest Java 8 date and time API is thread-safe, Java.util.Date was mutable and not thread-safe.
• In terms of performance, Java 8 is faster than the older date and time regime.

12. What is the difference between a Predicate and a Function?

A Predicate and a Function differ in the following respects:

• While Predicate has the return type as boolean, Function has the return type as the object.
• A Predicate is written as Predicate<T> and accepts a single argument. A Function also accepts a single argument but is written as Function<T,R>

Here, T denotes the type of input to the function, and R represents the type of result.

13. What are Stream APIs, and why do we need them?

Stream APIs are a new feature in Java 8, a special class used for processing objects from a source such as Collection.

Stream APIs are needed for:

• Supporting aggregate operations and simplifying processing
• Faster processing and better performance
• Supporting functional-style programming
• Parallel operations

14. What is the use of the limit() method in Java 8?

The Stream.limit() method is used for specifying the limit of the elements. If we specify the size of the limit(X), it will return the Stream of size ‘X.’

15. What are PermGen and MetaSpace?

Up to Java 7, PermGen was an area used by JVM to store classes. PermGen was replaced by MetaSpace in Java 8.

The major benefit of MetaSpace over PermGen is in terms of size. While PermGen had a fixed maximum size and could not grow dynamically, MetaSpace does not have any size constraint and is capable of dynamic growth.

Here’s What You Can Do Next

Preparing for tech interviews can be a real hassle if you are not prepared well. By preparation, we do not simply mean going through truckloads of mock questions but also ensuring that your fundamentals are clear as crystal. And what better way to taking the first step towards your goals than signing up with upGrad?

upGrad is a leading online higher education platform offering industry-relevant programs and courses in collaboration with the best-in-class faculty and experts. With top university partners including Liverpool John Moores University, IIIT Bangalore, IIT Madras, and Duke Corporate Education, upGrad amalgamates the best teaching practices and latest technology to provide an immersive and world-class learning experience. upGrad’s educational programs and courses have impacted over 500,000 working professionals. In addition, it has a paid learner base of over 40,000 spread across more than 85 countries.

If you wish to pursue a career in software development or related fields, upGrad’s Master of Science in Computer Science and Executive PG Program in Software Development are two courses you should check out. With upGrad 360-degree career support, peer learning opportunities, and industry networking, the unique programs are curated to help learners master the know-how of software development. 

1. Master of Science in Computer Science (19 months) Program Highlights:

• Master’s degree from the prestigious Liverpool John Moores University.
• Six unique specializations to choose from – Big Data, Full Stack Development, Blockchain Development, DevOps, Cloud Computing, and Cyber Security.
• Comprehensive coverage of 30+ programming languages, tools, and software with four years of unlimited content access.
• More than 500 hours of content with 30+ case studies and projects, 10+ live sessions, and industry mentorship

2. Executive PG Program in Software Development (13 months) Program Highlights:

• Recognition from the prestigious IIIT Bangalore.
• Six unique specializations to choose from – Big Data, Full Stack Development, Blockchain Development, DevOps, Cloud Computing, and Cyber Security.
• Hands-on exposure to over 30 industry-relevant assignments, case studies, and projects with coverage of 30+ tools and software.
• 400+ hours of content, over ten live sessions, and mentorship from leading faculty and industry experts.

Conclusion

Having a relevant academic degree is the first step towards a bright career in software development. upGrad’s robust courses in Computer Science and Software Development are designed to prepare candidates for varied job roles, including that of Software Developer, Big Data Developer, Data Engineer, Big Data Engineer, and Big Data Architect. The next step is preparing for the job interviews, where questions on the various programming languages and tools are pretty typical. Java being the programming language of choice for developers across multiple platforms, Java 8 interview questions are mandatory in the interviewee’s preparation agenda.