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Apr 23, 2024 · Most Frequently Asked Java 8 Coding and Programming Interview Questions and Answers. Question 1: Write a Java 8 program to filter even numbers from a list ? Question 2: Write a Java 8 program to calculate the sum of integers in a list ?
- Explain the concept of a dictionary in programming. What are some common uses for a dictionary? A dictionary in programming is a data structure that stores key-value pairs.
- What is the time complexity of accessing a key in a dictionary? Please justify your answer. Accessing a key in a dictionary, also known as a hash table or map, has an average time complexity of O(1).
- Can a dictionary contain duplicate keys? What happens when you try to insert a duplicate key? No, a dictionary cannot contain duplicate keys. This is because dictionaries are implemented as hash tables, which require unique keys for indexing values.
- How would you check if a key exists in a dictionary without using a try/except block? In Python, you can check if a key exists in a dictionary without using a try/except block by utilizing the “in” keyword.
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- Can you explain the changes to the Java memory model in Java 8? Java 8 introduced several changes to the Java memory model, primarily aimed at improving performance and concurrency.
- How does the introduction of lambda expressions in Java 8 alter the way we code? Could you provide an example? Lambda expressions in Java 8 have revolutionized coding by introducing functional programming, reducing verbosity, and enhancing readability.
- What is the advantage of using the Stream API and how would you use it in a practical setting? The Stream API in Java 8 provides a new abstraction of working with sequences of elements, offering advantages like parallel execution and functional programming.
- Can you differentiate between the Optional class in Java 8 and the null references in previous versions? Java 8 introduced the Optional class to address issues with null references.
Find the best 55 Java 8 interview questions and 20 sample answers to evaluate candidates’ skills and hire the best developers for your team.
- Introduction
- Method References
- Optional
- Functional Interfaces
- Default Method
- Lambda Expressions
- Nashorn Javascript
- Streams
- Java 8 Date and Time API
- Conclusion
In this tutorial, we’re going to explore some of the JDK8-related questions that might pop up during an interview. Java 8 is a platform release packed with new language features and library classes. Most of these new features are geared towards achieving cleaner and more compact code, while some add new functionality that has never before been supp...
Q1. What Is a Method Reference?
A method reference is a Java 8 construct that can be used for referencing a method without invoking it. It’s used for treating methods as Lambda Expressions. They only work as syntactic sugar to reduce the verbosity of some lambdas. This way the following code: Can become: A method reference can be identified by a double colon separating a class or object name, and the name of the method. It has different variations, such as constructor reference: Static method reference: Bound instance metho...
Q2. What Is the Meaning of String::Valueof Expression?
It’s a static method reference to the valueOf method of the Stringclass.
Q1. What Is Optional? How Can It Be Used?
Optionalis a new class in Java 8 that encapsulates an optional value, i.e. a value that is either there or not. It’s a wrapper around an object, and we can think of it as a container of zero or one element. Optional has a special Optional.empty() value instead of wrapped null. Thus it can be used instead of a nullable value to get rid of NullPointerExceptionin many cases. We can read a dedicated article about Optional here. The main purpose of Optional, as designed by its creators, is to be a...
Q1. Describe Some of the Functional Interfaces in the Standard Library
There are a lot of functional interfaces in the java.util.functionpackage. The more common ones include, but are not limited to: 1. Function– it takes one argument and returns a result 2. Consumer– it takes one argument and returns no result (represents a side effect) 3. Supplier– it takes no arguments and returns a result 4. Predicate– it takes one argument and returns a boolean 5. BiFunction– it takes two arguments and returns a result 6. BinaryOperator – it is similar to a BiFunction, taki...
Q2. What Is a Functional Interface? What Are the Rules of Defining a Functional Interface?
A functional interface is an interface with one single abstract method (defaultmethods do not count), no more, no less. Where an instance of such an interface is required, a Lambda Expression can be used instead. More formally put: Functional interfacesprovide target types for lambda expressions and method references. The arguments and return type of such an expression directly match those of the single abstract method. For instance, the Runnableinterface is a functional interface, so instead...
Q1. What Is a Default Method and When Do We Use It?
A default method is a method with an implementation, which can be found in an interface. We can use a default method to add a new functionality to an interface, while maintaining backward compatibility with classes that are already implementing the interface: Usually when we add a new abstract method to an interface, all implementing classes will break until they implement the new abstract method. In Java 8, this problem was solved by using the default method. For example, the Collection inte...
Q2. Will the Following Code Compile?
Yes, the code will compile because it follows the functional interface specification of defining only a single abstract method. The second method, count, is a default method that does not increase the abstract method count.
Q1. What Is a Lambda Expression and What Is It Used For?
In very simple terms, a lambda expression is a function that we can reference and pass around as an object. Moreover, lambda expressions introduce functional style processing in Java, and facilitate the writing of compact and easy-to-read code. As a result, lambda expressions are a natural replacement for anonymous classes such as method arguments. One of their main uses is to define inline implementations of functional interfaces.
Q2. Explain the Syntax and Characteristics of a Lambda Expression
A lambda expression consists of two parts, the parameter part and the expressions part separated by a forward arrow: Any lambda expression has the following characteristics: 1. Optional type declaration – when declaring the parameters on the left-hand side of the lambda, we don’t need to declare their types as the compiler can infer them from their values. So int param -> … and param ->…are all valid 2. Optional parentheses – when only a single parameter is declared, we don’t need to place it...
Q1. What Is Nashorn in Java8?
Nashornis the new Javascript processing engine for the Java platform that shipped with Java 8. Until JDK 7, the Java platform used Mozilla Rhino for the same purpose, as a Javascript processing engine. Nashorn provides better compliance with the ECMA normalized JavaScript specification and better runtime performance than its predecessor.
Q2. What Is JJS?
In Java 8, jjsis the new executable or command line tool we use to execute Javascript code at the console.
Q1. What Is a Stream? How Does It Differ From a Collection?
In simple terms, a stream is an iterator whose role is to accept a set of actions to apply on each of the elements it contains. Thestream represents a sequence of objects from a source such as a collection, which supports aggregate operations. They were designed to make collection processing simple and concise. Contrary to the collections, the logic of iteration is implemented inside the stream, so we can use methods like map and flatMapfor performing a declarative processing. Additionally, t...
Q2. What Is the Difference Between Intermediate and Terminal Operations?
We combine stream operations into pipelines to process streams. All operations are either intermediate or terminal. Intermediate operations are those operations that return Streamitself, allowing for further operations on a stream. These operations are always lazy, i.e. they do not process the stream at the call site. An intermediate operation can only process data when there is a terminal operation. Some of the intermediate operations are filter, map and flatMap. In contrast, terminal operat...
Q3. What Is the Difference Between Map and flatMap Stream Operation?
There is a difference in signature between map and flatMap. Generally speaking, a map operation wraps its return value inside its ordinal type, while flatMapdoes not. For example, in Optional, a map operation would return Optional type, while flatMap would return Stringtype. So after mapping, we need to unwrap (read “flatten”) the object to retrieve the value, whereas after flat mapping, there is no such need as the object is already flattened. We apply the same concept to mapping and...
Q1. Tell Us About the New Date and Time API in Java 8
A long-standing problem for Java developers has been the inadequate support for the date and time manipulations required by ordinary developers. The existing classes such as java.util.Date and SimpleDateFormatteraren’t thread-safe, leading to potential concurrency issues for users. Poor API design is also a reality in the old Java Data API. Here’s just a quick example: years in java.util.Datestart at 1900, months start at 1, and days start at 0, which is not very intuitive. These issues and s...
In this article, we explored several important technical interview questions with a bias on Java 8. This is by no means an exhaustive list, but it contains questions that we think are most likely to appear in each new feature of Java 8. Even if we’re just starting out, ignorance of Java 8 isn’t a good way to go into an interview, especially when Ja...
Supplier – takes no arguments and returns a result. Predicate – takes one argument and returns a boolean. BiFunction – takes two arguments and returns a result. BinaryOperator – is similar to a BiFunction, taking two arguments and returning a result. The two arguments and the result are all of the same type. 13.
Without any further ado, here is a list of some of the common yet popular functional programming and Stream interview questions for Java programmers. If you have any other Java functional programming questions or anything related to JDK 8 Stream API, feel free to share with us, and I'll try to find an answer for you. 1.
