Java is a widely used programming language, with its applications ranging from Android to the Internet of Things. According to Codeplatoon, Java was the most popular job posting language in 2019. Given its widespread use, it’s no wonder that there’s still a considerable need for Java experts. Therefore, having extensive knowledge and understanding of Java still holds an important place in the job market.
Considering the need for Java experts in this AI-influenced era, Deliverydevs has evaluated the facts and focused on the most often-asked questions of Java 8. Once you’ve gone through all the questions of this blog, you’ll be in a better position to ace the key interview!
Java 8 Interview Questions—Basic Level
Here are some basic Java 8 interview questions for the first round of interviews.
1. What are the newly added features in Java 8?
Java 8 added significant features to the language and platform. Some major features are:
Lambda expressions: Lambda expressions allow developers to leverage functional programming ideas to write cleaner and more concise code. They simplify the structure for declaring anonymous functions, which makes it easier to work with collections and perform operations like filtering, narrowing, and mapping.
The Stream API: The Stream API introduces a modern approach to working with collections in Java. Using functional-style operations, it lets developers perform bulk operations on collections, such as filtering, mapping, sorting, and aggregating. Streams enable more declarative and brief code, which enhances readability and reduces boilerplate code.
Default and Static Methods in Interfaces: Java 8 allows interfaces to specify default and static methods. Default methods enable interfaces to define methods that don’t affect how current implementations work, while static methods let interfaces include useful methods that can be called without an instance.
New Date and Time API: Java 8 introduced the Java.time package, a contemporary date and time API to address the limitations in the previous java.util.Date and java.util.Calendar classes. The new API is more complete, flexible, and easy to use. It supports more tasks, such as date math, time zones, and formatting.
2. Why was a new version of Java needed in the first place?
There are two primary causes:
- Advancements in multi-core CPUs necessitated optimizations in Java to better support parallel and concurrent programming.
- Introduce support for modern functional programming paradigms, enabling cleaner, more expressive, and efficient code structures.
3. So, what actual advantages does Java 8 bring?
The advantages include:
- More readable and concise code with functional programming.
- Enhanced reusability via default interface methods.
- Better maintainability and testability.
- Improved concurrency and scalability with parallel streams.
- Efficient data operations similar to database queries.
4. What are Lambda Expressions, and why are they used?
Lambda expressions are anonymous functions that can be treated as objects. They allow users to bundle a single action into a concise code unit that can be passed as a parameter to other functions. They support functional interfaces in Java 8 and help reduce boilerplate code.
5. What is a functional interface?
A functional interface in Java is an interface with exactly one abstract method. It’s also known as a Single Abstract Method (SAM) interface. Functional interfaces serve as the foundation for lambda expressions and other functional programming features introduced in Java 8.
A functional interface may also include default methods, static methods, or abstract methods inherited from the Object class. However, it must strictly have only one abstract method to qualify as a functional interface.
Functional interfaces in Java enable behaviors to be treated as first-class citizens, allowing the use of lambda expressions to represent the interface’s single abstract method. This leads to more concise, readable code and streamlined operations when working with APIs designed to accept functional interfaces as parameters.
6. Did functional interfaces exist before Java? Or is it a new feature introduced in Java 8?
Functional interfaces existed before Java 8. They are not a new concept, as interfaces like Runnable, Comparator, and Callable have been part of Java for a long time. However, prior to Java 8, these interfaces were used with anonymous inner classes rather than lambda expressions. Java 8 introduced functional programming capabilities, including lambda expressions, which made the use of functional interfaces much cleaner and more concise.
7. In addition to Predicate and BiPredicate, what is the distinction between Function and BiFunction?
Function<T, R>: Represents a function that takes one input of type T and returns a result of type R.
BiFunction<T, U, R>: Represents a function that takes two inputs of types T and U, returning a result of type R.
Additionally:
Predicate<T>: Represents a function that takes one input of type T and returns a boolean result.
BiPredicate<T, U>: Represents a function that takes two inputs of types T and U and returns a boolean result.
8. What is the relationship between Lambda Expressions and functional interfaces?
Lambda expressions are closely tied to functional interfaces in Java. A functional interface contains only one abstract method, and lambda expressions provide a concise way to implement that method directly. This relationship allows developers to write cleaner and more readable code by avoiding verbose, anonymous inner classes.
9. Is it possible for users to develop a functional interface that is unique to them?
Yes, users can create custom functional interfaces in Java. A functional interface is defined using the FunctionalInterface annotation to ensure that it contains only one abstract method. However, it can also have default or static methods if done without any supervision.
10. In the context of Java 8, what is the meaning of the term "method reference"?
A method reference in Java 8 allows you to refer to an existing method by its name without executing it. It serves as a shorthand for lambda expressions, making the code cleaner and more readable.
Java 8 Interview Questions—Intermediate Level
Now that you know basic Java 8 interview questions, let’s begin with the intermediate-level questions.
11. What are the distinctions between streams and collections?
Data is primarily stored and organized in collections, while streams are predominantly employed to process data. Additionally, it is feasible to incorporate or eliminate elements from collections, but it is not possible to add or remove elements from streams.
Streams are internally iterated, whereas collections are iterated externally. Streams can only be traversed once, whereas collections can be traversed multiple times.
12. What is optional, and what is it most effective for?
Optional is a container class introduced in the java.util package to represent optional values that may or may not be present. Its primary advantage is reducing the need for explicit null checks, thereby helping to avoid “NullPointerException” errors at runtime.
13. What is the definition of type inference?
Type inference is a feature where the compiler deduces the types of arguments and variables by analyzing method calls and their declarations, eliminating the need for explicit type definitions.
14. Provide a list of a few Java 8 Date and Time APIs.
Included in the main API classes are:
- LocalDate
- LocalTime
- LocalDateTime
15. What is the necessity of default methods in the interface?
Default methods enable the addition of new functionality to the libraries’ interfaces and maintain binary compatibility with prior code that was written for the interfaces.
16. What is the purpose of the Java 8 StringJoiner class?
The StringJoiner class in Java 8 generates a sequence of characters that are separated by a delimiter. This allows users to generate a string by supplying delimiters, such as commas and hyphens.
17. What is a default method, and when is it implemented?
A default method in Java is defined within an interface that includes a concrete implementation. It allows interfaces to introduce new functionality without breaking existing implementations of the interface. Default methods are implemented when classes need to inherit behavior directly from the interface without requiring changes to their code. They help maintain backward compatibility while evolving the interface.
18. In Java 8, what is jjs?
jjs is a new command-line utility or executable utilized at the console to execute JavaScript code.
19. Which operations are undergoing reductions? List a few of the reducing operations that are available in the Java 8 streams.
Here are a few of the reducing operations that are available in Java 8 streams. \
- min(): It returns the minimum element
- max(): It returns the maximum element
- count(): It returns the number of elements
collect(): It returns a mutable result container
20. What are the selection operations available in the Java 8 Stream API?
Here are the selection operations given in the Java 8 Stream API:
- filter(): It selects the element that satisfies the given predicate.
- limit(): It selects the first n elements.
- distinct(): It selects unique elements.
- skip (): It selects the elements after going over the first n elements.
Java 8 Interview Questions—Experienced Level
Finally, here come the tough questions.
21. What is Nashorn, and what are its benefits?
Java 8 includes Nashorn, a new JavaScript processing engine. Previously, Mozilla Rhino was employed by the Java platform; however, Nashorn is more compliant with ECMA-normalized JavaScript specifications and offers quicker run-time performance than its predecessor.
22. What is the definition of stream pipelining?
Stream pipelining is the process of chaining multiple stream operations together in Java 8. It categorizes operations into:
- Intermediate operations: Return a new stream, allowing further operations to be chained (e.g., filter(), map(), sorted()).
- Terminal operations: Produce a result or a side effect and close the stream (e.g., forEach(), collect(), reduce()).
By combining intermediate operations followed by a terminal operation, users can build flexible and efficient data processing pipelines.
23. How do you print ten random numbers using forEach?
Use the following code segment:
Random random = new Random();
random.ints().limit(10).forEach(System.out::println);
24. How do you get the highest number that exists on a list?
Use the following code segment:
List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
IntSummaryStatistics stats = integers.stream().mapToInt((x) −> x).summaryStatistics();
System.out.println(“Lowest number in List : ” + stats.getMin());
25. How do you get the second Friday of next month?
Use the following code segment:
List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
IntSummaryStatistics stats = integers.stream().mapToInt((x) −> x).summaryStatistics();
System.out.println(“Lowest number in List : ” + stats.getMin());
