Java 8 short interview questions and answers

1. What is Java 8? Java 8 is a version of the Java programming language that was released in 2014. It introduced several new features that aimed to improve the productivity of developers and enhance the performance of Java applications.

1. What are the new features introduced in Java 8? Some of the new features introduced in Java 8 include lambda expressions, the Stream API, the Date and Time API, default methods in interfaces, and the Optional class.

1. What is a lambda expression? A lambda expression is a new feature introduced in Java 8 that allows you to pass a block of code as an argument to a method. It is similar to an anonymous inner class, but with a more concise syntax.

1. How does lambda expression work in Java 8? Lambda expressions work by creating a functional interface that defines a single abstract method. The lambda expression provides an implementation of that method, which can then be used as an argument to a method or passed around like any other object.

1. What is a functional interface? A functional interface is an interface that has only one abstract method. It is used in Java 8 to enable the use of lambda expressions.

1. Can we declare a method in an interface in Java 8? If yes, how? Yes, we can declare a method in an interface in Java 8 using the default keyword. A default method is a method that has an implementation in the interface itself.

1. What is the default method in an interface? A default method is a method that has an implementation in the interface itself. It allows you to add new methods to an interface without breaking the classes that implement it.

1. How does the Stream API work in Java 8?

2. The Stream API in Java 8 is used to process collections of objects. It allows you to perform aggregate operations on collections, such as filtering, mapping, and reducing, in a concise and efficient manner.

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2. What are the advantages of using the Stream API? The advantages of using the Stream API include improved performance, reduced code complexity, and improved readability.

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2. What is the difference between the map() and flatMap() methods in the Stream API? The map() method is used to transform each element in a stream into another element, whereas the flatMap() method is used to transform each element in a stream into a stream of elements, which are then flattened into a single stream.

1. How does the Optional class work in Java 8? The Optional class in Java 8 is used to represent a value that may or may not be present. It provides a way to handle null values in a more concise and safe manner.

1. What is the difference between a Supplier and a Consumer in Java 8? A Supplier is a functional interface that takes no arguments and returns a value, whereas a Consumer is a functional interface that takes an argument and returns no value.

1. How does the forEach() method work in Java 8? The forEach() method in Java 8 is used to iterate over a collection of elements and apply a function to each element.

1. What is the difference between parallelStream() and stream() methods in Java 8? The parallelStream() method in Java 8 is used to process a stream of elements in parallel, whereas the stream() method is used to process a stream of elements sequentially.

1. How does the Date and Time API work in Java 8? The Date and Time API in Java 8 provides a more comprehensive set of classes for working with dates and times. It includes classes such as LocalDate, LocalTime, LocalDateTime, and ZonedDateTime, which provide more functionality and flexibility than the Date and Calendar classes in previous versions of Java.