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Cheers, Eugen. 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 sdet interview questions java 64 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 supported in Java.
Along with these new features, lots sdet interview questions java 64 feature enhancements are done under the hood at both the compiler and JVM level. 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:.
Sdet interview questions java 64 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 sdet interview questions java 64 reference:.
We can read a detailed description of method references with full examples by following this link and this one. Optional is a new class in Java 8 that encapsulates an optional value, i.
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. Thus it can be used instead of a nullable value to get rid of NullPointerException in many cases. The main purpose of Optionalas designed by its creators, is to be sdet interview questions java 64 return type of methods that previously would return null.
Such methods would require us to write boilerplate code to check the return value, and we could sometimes forget to do a defensive check. In Java 8, an Optional return type explicitly requires us to handle null or non-null wrapped values differently. For instance, the Stream.
But what if the stream is empty? If it wasn't for Optionalthe method would return null or throw an exception. However, it sdet interview questions java 64 an Optional value, which may be Optional.
This allows us to easily handle such cases:. It's worth noting that Optional is not a general purpose class like Option in Scala. It's not recommended that we use it as a field value in entity classes, which is clearly indicated by Sdet Interview Questions Java Yoga it not implementing the Serializable interface. There are a lot of functional interfaces in the java. The more common ones include, but are not limited to:.
A functional interface is an interface with one single abstract method default methods do not countno more, no. Where an instance of such an interface is required, a Lambda Expression can be used instead. More formally put: Functional interfaces provide 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. Functional interfaces are usually annotated with the FunctionalInterface annotation, which is informative and doesn't affect the semantics.
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 interface does not have a forEach method declaration. Thus adding such a method would simply break the whole collections API. Java 8 introduced the default method so that the Collection interface can have a default implementation sdet interview questions java 64 the forEach method without requiring the classes implementing this interface to sdet interview questions java 64 the.
Yes, the code will compile because it follows the functional interface specification of defining only a single abstract method. The second method, countis a default method that does not increase the abstract method count. 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. A lambda expression consists of two parts, the parameter part and the expressions part separated by a forward arrow:.
To read more about Lambda expressions, follow this link and this one. Nashorn is the new Javascript processing engine for the Java platform that shipped with Java 8. Nashorn provides better compliance with the ECMA normalized JavaScript specification and better runtime performance than its predecessor.
In Java 8, jjs is the new executable or command line tool we use to execute Javascript code at the console. In simple terms, a stream is an iterator whose role is to accept a set of actions sdet interview questions java 64 apply on each of the elements it contains. The stream 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 flatMap for performing a declarative processing. Another important distinction from collections is that streams are inherently lazily loaded and processed. We combine stream operations into pipelines to process streams.
All operations are either intermediate sdet interview questions java 64 terminal. Intermediate operations are those operations Sdet Interview Questions C# Web that return Stream itself, allowing for further operations on a stream.
These operations are always lazy, i. An intermediate operation can only process data when there is a terminal operation.
Some of the intermediate operations are filtermap and flatMap. In contrast, terminal operations terminate the pipeline and initiate stream processing. The stream is passed through all intermediate operations during terminal operation.
Terminal operations include forEachreduce, Collect and sum. There is a difference in signature between map and flatMap. Generally speaking, a map operation wraps its return value inside its ordinal type, while flatMap does not. We apply the same concept to mapping and flat mapping in Stream. Both map and flatMap are intermediate stream operations sdet interview questions java 64 receive a function and apply this function to all sdet interview questions java 64 elements of a stream.
The difference is that for the mapthis function returns a value, but for flatMapthis function returns a stream. Stream pipelining is the concept of chaining operations. We do sdet interview questions java 64 by splitting the operations that can happen on a stream into two categories: intermediate operations and terminal operations.
Each intermediate operation returns an instance of Stream itself when it runs. Therefore, we can set up an arbitrary number of intermediate operations to process data, forming a processing pipeline. 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. Here's just a quick example: years in java. Date start atmonths start at 1, and days start at 0, which is not very intuitive. These issues and several others have led to the popularity of third-party date and time libraries, such as Joda-Time.
In order to address these problems and provide better support in JDK, a new date and time API, which is free of these problems, has been designed for Java SE 8 under the package java. 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 Java appears strongly on a resume. It is therefore important that we take some time to understand the answers to these questions and possibly sdet interview questions java 64 more research.
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