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Understanding Lazy Evaluation in Java Streams

Java Streams, introduced in Java 8, have revolutionized how we handle collections of data in Java. They offer a high-level, declarative approach to data processing, but one of their most intriguing features is lazy evaluation. This article delves into what lazy evaluation means in the context of Java Streams and why it's beneficial, accompanied by practical examples.

Basics of Java Streams

Java Streams provide a way to sequentially or parallelly process sequences of elements. A stream pipeline consists of a source (like collections), followed by zero or more intermediate operations and a terminal operation.

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Usage of Java Streams and Lambdas in Selenium WebDriver

Overview: Java Streams and Lambdas

Lambdas

A lambda expression is a microcode that takes in parameter(s) and returns a value. Lambda expressions are similar to methods, but they are anonymous and they can be implemented right in the body of a method.

Lambdas Syntax

Java
  
parameter -> expression //to use single parameter & expression
(parameter1, parameter2) -> expression //to use multiple parameters & expression
(parameter1, parameter2) -> {code block} //to use multiple parameters & conditions, loops and more complex logic


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Grouping and Aggregations With Java Streams

When we group elements from a list, we can subsequently aggregate the fields of the grouped elements to perform meaningful operations that help us analyze the data. Some examples are addition, averages, or max/min values. These aggregations of single fields can be easily done with Java Streams and Collectors. The documentation provides simple examples of how to do these types of calculations.

However, there are more sophisticated aggregations like weighted averages, geometric means. Additionally, there might be the need to do simultaneous aggregations of several fields. In this article, we are going to show a straightforward path to solve these kinds of problems using Java Streams. Using this framework allows us to process large amounts of data quickly and efficiently.

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Java Joy: Turn Streams Into Arrays [Snippet]

The Java Stream API has many useful methods. If we want to transform a Stream into a Java array, we can use the toArray method. Without an argument, the result is an object array ( Object[]), but we can also use an argument to return an array of another type. The easiest way is to use the contructor of the array type we want as a method reference. Then, the result is an array of the given type with the elements of the stream.

This is very useful if we have a Java Stream and want to use the elements to invoke a method with a variable arguments parameter. In Java, we can pass an array object as variable arguments argument to a method. So if we transform the Stream into an array we can invoke the method with that value.

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Anatomy of Sequential Data Processing With Java Streams

Functional Programming History

The history of functional programming can be traced back to Lambda-calculus. It is a mathematical language invented by Alonzo in 1930. In some ways, lambda-calculus is the first programming language. Some principles of lambda calculus can be found in modern functional languages and even in Java also. The first principle is that the main object in this kind of language is functions and functions in the mathematical sense of these words. something that takes input and returns the output.

It always returns the same output if based on the same input. Hence, this property goes by the name of being stateless. In other words, the function has no memory of previous inputs.

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Become a Master of Java Streams (Part 4): Database Streams

You can almost see the data flowing...

SQL has always been a declarative language whereas Java for a long time has been imperative. Java streams have changed the game. Code your way through this hands-on-lab article and learn how Java streams can be used to perform declarative queries to an RDBMS database, without writing a single line of SQL code. You will discover, there is a remarkable similarity between the verbs of Java streams and SQL commands.

Not quite what you're looking for? Take a look at Querying Databases Using Java Streams.

This article is the fourth out of five, complemented by a GitHub repository containing instructions and exercises to each unit.

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Become a Master of Java Streams, Part 2: Intermediate Operations

Want to become a Java Streams Master?

Just like a magic wand, an Intermediate operation transforms a Stream into another Stream. These operations can be combined in endless ways to perform anything from simple to highly complex tasks in a readable and efficient manner.

This article is the second out of five, complemented by a GitHub repository, containing instructions and exercises to each unit.