Java 8 Coding Interview Questions
Expert Guide to Ace Your Next Job Interview
Java 8 introduces new functional features like Lambda expressions, Stream API, and improved performance through the use of default and static methods in interfaces. As a result, Java 8 coding interview questions focus on these new features, as well as previous concepts like collections, multi-threading, and exception handling. Some common questions include the differences between a lambda expression and a method reference, how to use Stream API to process large data sets, and the benefits of using default methods in interfaces. Employers may also ask about the new Date and Time API, the concept of functional interfaces, and how to handle concurrency issues in Java 8. Overall, Java 8 coding interview questions aim to assess the candidate’s understanding of the new features and their ability to utilize them effectively in real-world scenarios.
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1 - What is a lambda expression?
A lambda expression in Java 8 is a new way to represent an anonymous function, which can be passed around as a variable and used in methods or data structures. It consists of two parts: parameters and a body. The parameters specify the inputs to the function, while the body defines the operations that will be performed on those inputs. Lambda expressions are used extensively with functional interfaces, which are interfaces that have only one abstract method.
2) How is a lambda expression different from a regular method?
Lambda expressions do not belong to any class and do not have any modifiers, while regular methods are associated with a class and can be public, private, or protected. Lambda expressions can be anonymous, meaning they do not have a name and can only be used once, while regular methods must have a unique name. Lambda expressions also have more concise syntax and can be used in functional programming techniques, unlike regular methods.
3) What are functional interfaces?
Functional interfaces in Java 8 are interfaces that have only one abstract method, but can also have default or static methods. Examples of functional interfaces include Runnable, Callable, and Predicate. These interfaces are used extensively with lambda expressions to enable functional programming in Java.
4) How is functional programming different from object-oriented programming?
Functional programming is a programming paradigm that focuses on writing code in a declarative manner, where problems are solved by creating and passing functions as arguments. Object-oriented programming, on the other hand, focuses on writing code in an imperative manner, where problems are solved by creating and manipulating objects. Functional programming allows for more concise and efficient code, while object-oriented programming promotes reusability and maintainability.
5) What is immutability and why is it important in functional programming?
Immutable objects are objects whose state cannot be changed after their creation. In functional programming, immutability is encouraged as it eliminates side effects and promotes code that is easier to understand and reason about. It also helps in creating thread-safe code and enables parallel processing and optimization.
6) What is the difference between a stream and a collection in Java 8?
A stream is a sequence of elements that supports aggregate operations on those elements. Streams are designed for bulk operations on data and can be used with lambda expressions to enable functional programming techniques. Collections, on the other hand, are data structures used to store and manipulate data. Collections can also be accessed randomly, while streams are accessed sequentially.
7) How can you handle null values in Java 8?
Java 8 introduced the Optional class to handle null values. Optional is a container object that may or may not contain a non-null value. It provides methods to check if a value is present and retrieve the value safely without worrying about a NullPointerException. Optional is widely used in Java 8 streams and is recommended for handling null values in functional programming.
8) What are method references in Java 8?
Method references in Java 8 provide a shorthand syntax for lambda expressions to refer to an existing method. They consist of the method name followed by double colons (::) and can be used with functional interfaces that have a compatible method signature. Method references can help in writing more concise and readable code by reducing the use of lambda expressions.
9) What is a default method in an interface?
A default method in an interface is a method with a default implementation. They were introduced in Java 8 to allow interfaces to have concrete methods, unlike previous versions where all methods in an interface were abstract. Default methods can be overridden by implementing classes, and they provide a way to add new functionality to existing interfaces without breaking their implementation.
10) What is a static method in an interface?
A static method in an interface is a method that can be called without an instance of the interface. They were also introduced in Java 8 and can only be accessed within the interface. Static methods can be used to provide utility methods or support methods for other methods in the interface.
11) How do you make use of parallel streams in Java 8?
Parallel streams in Java 8 allow for parallel processing of data, which can significantly improve performance for large datasets. To make use of parallel streams, the collection or array must first be converted into a stream using the stream() or parallelStream() methods. Then the parallel() method can be called on the stream to execute operations in parallel.
12) What is the purpose of the forEach() method in Java 8 streams?
The forEach() method in Java 8 streams allows for performing an action on each element of the stream. It can be used to loop through and print out the elements of a collection or to modify the elements in some way. It can also be used to process the elements in parallel using parallel streams.
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13) What is the use of the Collectors class in Java 8 streams?
The Collectors class in Java 8 streams provides several useful methods for collecting and reducing data from streams into a single object. These methods include summing, averaging, grouping, and groupingBy. The Collectors class can be used with the collect() method to apply the specified reduction operation on the stream elements.
14) What is a spliterator in Java 8?
A spliterator (short for “splitable iterator”) in Java 8 is an interface that enables iterating over a collection or a stream and allowing that iteration to be split into multiple parts. Spliterators are used internally by Java 8 streams to process large collections in parallel. They can also be used to customize the traversal and splitting behavior of streams.
15) How does Java 8 support functional programming in terms of error handling?
Java 8 introduced the concept of functional interfaces with the annotation @FunctionalInterface, which allows for the declaration of checked exceptions in lambdas. This means that any checked exceptions that may occur in a lambda expression must be declared in the functional interface's abstract method. This provides a way to handle exceptions in functional programming without breaking the functional interface's contract.
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