Book Image

Apache Spark 2.x for Java Developers

By : Sourav Gulati, Sumit Kumar
Book Image

Apache Spark 2.x for Java Developers

By: Sourav Gulati, Sumit Kumar

Overview of this book

Apache Spark is the buzzword in the big data industry right now, especially with the increasing need for real-time streaming and data processing. While Spark is built on Scala, the Spark Java API exposes all the Spark features available in the Scala version for Java developers. This book will show you how you can implement various functionalities of the Apache Spark framework in Java, without stepping out of your comfort zone. The book starts with an introduction to the Apache Spark 2.x ecosystem, followed by explaining how to install and configure Spark, and refreshes the Java concepts that will be useful to you when consuming Apache Spark's APIs. You will explore RDD and its associated common Action and Transformation Java APIs, set up a production-like clustered environment, and work with Spark SQL. Moving on, you will perform near-real-time processing with Spark streaming, Machine Learning analytics with Spark MLlib, and graph processing with GraphX, all using various Java packages. By the end of the book, you will have a solid foundation in implementing components in the Spark framework in Java to build fast, real-time applications.
Table of Contents (19 chapters)
Title Page
About the Authors
About the Reviewer
Customer Feedback

Lexical scoping

Lexical scoping is also referred to as Static scoping. As per lexical scoping, a variable will be accessible in the scope in which it is defined. Here, the scope of the variable is determined at compile time.

Let us consider the following example:

public class LexicalScoping { 
   int a = 1; 
   // a has class level scope. So It will be available to be accessed 
   // throughout the class 
   public void sumAndPrint() { 
      int b = 1; 
      int c = a + b; 
      // b and c are local variables of method. These will be accessible 
      // inside the method only 
   // b and c are no longer accessible 

Variable a will be available throughout the class (let's not consider the difference of static and non-static as of now). However, variables b and c will be available inside the sumAndPrint method only.

Similarly, a variable given inside lambda expressions are accessible only to that Lambda. For example: -> n*2 ); 

Here n is lexically scoped to...