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Learning Java Functional Programming
Learning Java Functional Programming

Learning Java Functional Programming: Create robust and maintainable Java applications using the functional style of programming

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Profile Icon Richard M Reese Profile Icon Richard M. Reese
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Paperback Oct 2015 296 pages 1st Edition
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Arrow left icon
Profile Icon Richard M Reese Profile Icon Richard M. Reese
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₹800 per month
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Paperback Oct 2015 296 pages 1st Edition
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Learning Java Functional Programming

Chapter 2. Putting the Function in Functional Programming

In the first chapter, the basic concept of functions and how they are supported by lambda expressions in Java 8 were introduced. In this chapter, we will cover lambda expressions in more depth. We will explain how they satisfy the mathematical definition of a function and how we can use them in supporting Java applications.

In this chapter, you will cover several topics, including:

  • Lambda expression syntax and type inference
  • High-order, pure, and first-class functions
  • Referential transparency
  • Closure and currying
  • Common functional interfaces

Our discussions cover high-order functions, first-class functions, and pure functions. Also examined are the concepts of referential transparency, closure, and currying. Examples of nonfunctional approaches are followed by their functional equivalent where practical.

While we used lambda expression extensively in our examples, in the last part of this chapter, a little time will be spent examining...

Lambda expressions usage

A lambda expression can be used in many different situations, including:

  • Assigned to a variable
  • Passed as a parameter
  • Returned from a function or method

We will demonstrate how each of these is accomplished and then elaborate on the use of functional interfaces. As you may remember from Chapter 1, Getting Started with Functional Programming, a functional interface is an interface that has one and only one abstract method.

Consider the forEach method supported by several classes and interfaces, including the List interface. In the following example, a List interface is created and the forEach method is executed against it. The forEach method expects an object that implements the Consumer interface. This will display the three cartoon character names:

    List<String> list = Arrays.asList("Huey", "Duey", "Luey");
    list.forEach(/* Implementation of Consumer Interface*/);

More specifically, the forEach method expects an object that implements...

Functional programming concepts in Java

In this section, we will examine the underlying concept of functions and how they are implemented in Java 8. This includes high-order, first-class, and pure functions.

A first-class function is a function that can be used where other first-class entities can be used. These types of entities include primitive data types and objects. Typically, they can be passed to and returned from functions and methods. In addition, they can be assigned to variables.

A high-order function either takes another function as an argument or returns a function as the return value. Languages that support this type of function are more flexible. They allow a more natural flow and composition of operations. The use of composition is explored in Chapter 3, Function Composition and Fluent Interfaces.

Pure functions have no side effects. The function does not modify nonlocal variables and does not perform I/O.

High-order functions

We will demonstrate the creation and use of the high...

Lambda expressions revisited

In this section, we will explore the syntax of lambda expression in more depth. So far, we used them without formally describing them. We will also examine other forms they can take.

As mentioned earlier, a lambda expression is essentially an anonymous function. They can be passed to another function or method, returned from a function or a method, and assigned to variables.

A lambda expression consists of an optional parameter list, followed by the lambda operator, and then a body. The lambda operator is a dash followed by the greater than symbol. The body of a lambda expression may be one or more statements and may optionally return a value.

Let's examine several variations of a simple lambda expression. A single value is passed to the function. This value is incremented and then returned. Several equivalent variations of this function are illustrated in the following table:

Variation

Comment

x -> x + 1

The simplest form of the function

(x) -&gt...

Functional interfaces revisited

We used several functional interfaces in the previous examples. In this section, we will examine in more detail how they are created and illustrate a number of predefined functional interfaces available for immediate use in Java 8.

As mentioned earlier, a functional interface is an interface that has one and only one abstract method. It may have zero or more default methods. Since the interface has only one abstract method, the system is able to know which method to match to a lambda expression. This abstract method is called the functional method.

Creating a functional interface

The IntegerConcatenation interface is duplicated here as an example. Note the use of the @FunctionalInterface annotation. While not required, it will generate a syntax error if the interface is not a functional interface:

@FunctionalInterface
public interface IntegerConcatenation {
    public String concatenate(Integer n1, Integer n2);
}

Functional interfaces are easy to create. After...

Summary

In this chapter, we investigated the use of lambda expressions and how they support the functional style of programming in Java 8. When possible, we used examples to contrast the use of classes and methods against the use of functions. This frequently led to simpler and more maintainable functional implementations.

We illustrated how lambda expressions support the functional concepts of high-order, first-class, and pure functions. Examples were used to help clarify the concept of referential transparency. The concepts of closure and currying are found in most functional programming languages. We provide examples of how they are supported in Java 8.

Lambda expressions have a specific syntax, which we examined in more detail. Also, there are several ways of expressing a la­mbda expression which we illustrated. Lambda expressions are based on functional interfaces using type inference. It is important to understand how to create functional interfaces and to know what standard functional...

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Key benefits

  • • Explore how you can blend object-oriented and functional programming styles in Java
  • • Use lambda expressions to write flexible and succinct code
  • • A tutorial that strengthens your fundamentals in functional programming techniques to enhance your applications

Description

Functional programming is an increasingly popular technology that allows you to simplify many tasks that are often cumbersome and awkward using an object-oriented approach. It is important to understand this approach and know how and when to apply it. Functional programming requires a different mindset, but once mastered it can be very rewarding. This book simplifies the learning process as a problem is described followed by its implementation using an object-oriented approach and then a solution is provided using appropriate functional programming techniques. Writing succinct and maintainable code is facilitated by many functional programming techniques including lambda expressions and streams. In this book, you will see numerous examples of how these techniques can be applied starting with an introduction to lambda expressions. Next, you will see how they can replace older approaches and be combined to achieve surprisingly elegant solutions to problems. This is followed by the investigation of related concepts such as the Optional class and monads, which offer an additional approach to handle problems. Design patterns have been instrumental in solving common problems. You will learn how these are enhanced with functional techniques. To transition from an object-oriented approach to a functional one, it is useful to have IDE support. IDE tools to refactor, debug, and test functional programs are demonstrated through the chapters. The end of the book brings together many of these functional programming techniques to create a more comprehensive application. You will find this book a very useful resource to learn and apply functional programming techniques in Java.

Who is this book for?

If you are a Java developer with object-oriented experience and want to use a functional programming approach in your applications, then this book is for you. All you need to get started is familiarity with basic Java object-oriented programming concepts.

What you will learn

  • • Use lambda expressions to simplyfy code
  • • Use function composition to achieve code fluency
  • • Apply streams to simply implementations and achieve parallelism
  • • Incorporate recursion to support an application's functionality
  • • Provide more robust implementations using Optionals
  • • Implement design patterns with less code
  • • Refactor object-oriented code to create a functional solution
  • • Use debugging and testing techniques specific to functional programs

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Publication date : Oct 14, 2015
Length: 296 pages
Edition : 1st
Language : English
ISBN-13 : 9781783558483
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Publication date : Oct 14, 2015
Length: 296 pages
Edition : 1st
Language : English
ISBN-13 : 9781783558483
Category :
Languages :

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Table of Contents

10 Chapters
1. Getting Started with Functional Programming Chevron down icon Chevron up icon
2. Putting the Function in Functional Programming Chevron down icon Chevron up icon
3. Function Composition and Fluent Interfaces Chevron down icon Chevron up icon
4. Streams and the Evaluation of Expressions Chevron down icon Chevron up icon
5. Recursion Techniques in Java 8 Chevron down icon Chevron up icon
6. Optional and Monads Chevron down icon Chevron up icon
7. Supporting Design Patterns Using Functional Programming Chevron down icon Chevron up icon
8. Refactoring, Debugging, and Testing Chevron down icon Chevron up icon
9. Bringing It All Together Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
(1 Ratings)
5 star 0%
4 star 0%
3 star 100%
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1 star 0%
Waldorf Jan 09, 2016
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
I've been reading the Safari Online version of this book and it contains a lot of useful information. I would have given the book 4 stars but for the fact that the book has many, many typos, which is not good for a technical book. There are minor mistakes like misspellings and not matching the plurality of subjects and verbs, but there are also more important mistakes, such as errors in the code examples in the book and in the specifications of classes and interfaces. For example, in Chapter 2, where functional interfaces are discussed, the book says that the functional method in the BinaryOperator<T> interface has return type R, when it should have said T. Similarly, the book says that the getAsInt( ) method in the IntSupplier interface has return type R, when it should have said int. This book was not sufficiently proofread before publication.
Amazon Verified review Amazon
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