Top 40 Java 8 Interview Questions & Answers for 2023
Did you know, as per the U.S. Bureau of Labor Statistics, Java was the most commonly mentioned in developer job postings, with each appearing in over 50,000 job listings?
For your team, you should evaluate a number of abilities if you want to hire a top Java developer.
Your upcoming hire should possess the appropriate technical abilities, soft skills, and values that complement your business culture.
A simple method for assessing the abilities of your applicants is candidate interviews. What if, however, you don't have the appropriate interview questions at this time?
There's no need to worry; in this post, you'll find typical Java 8 interview questions that you can use to evaluate the Java coding abilities and expertise of your applicants.
To create a list of questions, look over the list below.
1. What does "Java 8 supports Functional Programming" mean?
Before Java 8, everything was primarily object-oriented. Except for primitives, everything in Java was an object.
All method/function calls must be done using objects or class references. Methods/Functions did not exist on their own.
Functional programming was introduced in Java 8. As a result, we can employ anonymous functions. Java is a first-rate object-oriented programming language. Everything in Java, with the exception of rudimentary data types, is an object. An array is also an Object. Every class generates elements. There is no way to define a single function or method that will remain in Java on its own.
There is no technique to send a method as a parameter or return the body of a method for that object.
2. What new features did Java 8 bring?
The most recent version includes:
- An enhanced, immutable Date and Time API inspired by JodaTime
- Lambda Expressions is a new language that considers actions as objects.
- Method References, which allow you to define Lambda Expressions by referring to methods by their names directly.
- In addition to abstract methods, default methods allow users to add full implementations to interfaces.
- Nashorn, a high-performance Java-based engine incorporated into JDK that is used to analyze and execute JavaScript code Stream API, a specific iterator class that allows functionally processing object collections
3. What exactly are Lambda expressions?
It is a function that may be referenced and shared in the form of an object. Lambda Expressions provide less writing, allow for the implementation of the Java 8 functional interface, and allow users to encapsulate one behavior unit to pass around to other programs.
4. Describe the most common functional interfaces present in the standard library.
Although numerous functional interfaces exist, the following are the ones that users are most likely to encounter:
- Function: This function takes one parameter and returns a result.
- Consumer: Takes one argument and produces no output.
- Supplier: This function takes a not parameter and produces a result.
- Predicate: Returns a boolean function with one argument. This function takes two arguments and produces a result.
- BinaryOperator: It's similar to a function in that it accepts two parameters and returns a result of the same type.
- UnaryOperator: It's similar to a Function, except it just accepts one parameter and produces the same type of result.
5. What exactly is a default method, and when is it used?
The interface contains the implementation for the default method. The technique extends an interface with additional functionality while maintaining backward compatibility with classes that currently implement the interface.
6. In the context of Java 8, what does the word "method reference" mean?
A method reference is a Java 8 concept that allows you to refer to a method without having to call it. It is a short approach to expressing Lambda.
7. In Interfaces, what are static methods?
Static methods, which include method specification and are executed using the interface's name, are excellent for providing utility methods that cannot be customized.
8. Stream API: What Is It? Why is the Stream API necessary?
In Java 8, a new feature called Stream API was introduced. It is a unique class used for handling items from sources like collections.
9. What Java 8 default methods are there?
The interfaces in Java 8 that utilize the keyword "default" are known as default methods. Java 8 now has default methods to provide users with functionality and backward compatibility.
10. What does Java 8's JJS mean?
The common line tool that comes with Java 8 is called JJS. It allows for smooth execution of JavaScript code through the console.
11. Can Java 8 code be used to execute JavaScript code?
Yes, by utilizing ScriptEngineManger, JavaScript code may be simply performed using codebase. In Java 8, this is used to understand the code.
12. What does Java 8's Nashorn mean?
The Java-based engine Nashorn in Java 8 is used to run and evaluate JavaScript code.
13. What do Java 8's ChronoUnits do?
The enum ChronoUnits was created to take the place of the Integer values that the former API used to indicate the month, day, etc.
14. What is the relationship between functional interfaces and Lambda Expressions?
Lambda expressions are only used in the abstract method of the functional interface.
15. Can people design their functional interface?
Yes, They certainly can.
16. What exactly is the String::ValueOf expression?
It is a static method reference to the String class's function Valueof(). It will return the string representation of the provided argument.
17. What exactly is Type Inference?
By inspecting each method invocation and related declaration, type inference assists the compiler in determining the parameter types.
18. List a number of the Java 8 Date and Time APIs.
The following are the primary API classes:
- LocalDate
- LocalTime
- LocalDateTime
19. What are the primary elements of a Stream?
The stream's components are as follows:
- a source of information
- a collection of intermediate operations for processing the data source
- The outcome is produced by a single terminal operation.
20. Why isn't Java entirely object-oriented?
Java is not entirely object-oriented since it uses eight primitive data types that are not objects, such as boolean, byte, char, int, float, double, long, and short.
21. What is the StringJoiner class in Java 8 used for?
The StringJoiner class in Java 8 creates a series of characters separated by a delimiter, allowing users to generate strings by passing delimiters such as hyphens and commas.
22. Is it required to annotate a Functional Interface with @Functionalinterface?
No, the @Functionalinterface annotation is not required to define a functional interface.
23. What exactly is a Spliterator?
The phrase derives from the words "splittable" and "iterator," and it is a new feature in Java SE 8. Internal iteration is used in the Stream API to iterate streams in parallel or sequential order.
24. What is the primary distinction between Map and FlatMap stream operations?
The primary distinction between Map and FlatMap stream operations is that the former wraps its return value within its ordinal type, whilst the latter does not.
25. What are the similarities and differences between Map and Flat map stream operations?
The Map and FlatMap stream operations are both intermediate stream operations that take a function and apply it to distinct parts of the stream.
26. What are the benefits of Metaspace versus PermGen?
PerGen had a set size and could not grow dynamically, but Metaspace can grow dynamically and has no size constraints.
27. Can we use Java SE 8 characteristics to list the numbers and eliminate duplicate entries from the list?
Yes, we can use a stream to list the numbers and then gather them to set using the Collections.toSet() function to eliminate duplicates.
28. What is the distinction between a Predicate and a BiPredicate?
A predicate is a functional interface that represents a one-argument boolean operation.
BiPredicate is a functional interface as well, but it represents a boolean operation with two arguments.
29. Which functional interface should you use if you wish to conduct actions on an object while returning nothing?
Consumer
30. Which functional interface is most suited for a procedure that generates new objects?
Supplier
31. What exactly is a short circuit operation?
Short-circuiting operations are those that do not require the entire stream to be processed to provide a result. For example, findFirst(), findAny(), limit(), and so forth.
32. If you have a list of workers, how do you determine the number of employees in each department?
Map<String, Long> employeeCountByDepartment=
employeeList.stream().collect(Collectors.groupingBy(Employee::getDepartment, Collectors.counting()));
33. In Java 8, what sorting operations are available?
In Java 8 streams, there is just one sorting operation available, which is sorted (). There are two variations. One accepts no arguments and sorts the components in natural order, while another takes an argument and sorts the elements according to the specified Comparator.
34. How do you determine who is the most senior employee in a company, given a list of employees?
Optional<Employee> seniorMostEmployeeWrapper=
employeeList.stream().sorted(Comparator.comparingInt(Employee::getYearOfJoining))
.findFirst();
35. How do you find the highest number on a list?
Use the 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());
36. What are the most significant Data and Time API packages?
- Java.time.format
- Java.time.temporal
- java.time
- dates
- times
- Instants
- durations
- time-zones
- periods
- java.time.zone
37. What are the benefits of Optional?
Optional has the following benefits.
- It assists in avoiding null checks.
- It prevents "NullPointerException" from occurring.
38. What exactly do you mean by SAM interface?
A functional interface was introduced in Java 8. Because a functional interface can only include one abstract method, they are referred to as SAM, or "Single Abstract Method."
39. What is the meaning of String::valueOf expression?
It is a reference to a static method of the String class, namely the function valueOf() { [native code] } method.
40. What is the reason for Java's neutrality?
Java is referred to as platform-neutral due to its byte codes, which may execute on any system regardless of its underlying operating system.
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