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  • Book Overview & Buying Java 9 with JShell
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Java 9 with JShell

Java 9 with JShell

By : Gastón C. Hillar
2 (2)
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Java 9 with JShell

Java 9 with JShell

2 (2)
By: Gastón C. Hillar
Buy this Book

Overview of this book

The release of Java 9 has brought many subtle and not-so-subtle changes to the way in which Java programmers approach their code. The most important ones are definitely the availability of a REPL, known as JShell, which will make experiments and prototyping much more straightforward than the old IDE-based project-led approach. Another, more subtle change can be seen in the module system, which will lead to more modularized, maintainable code. The techniques to take full advantage of object-oriented code, functional programming and the new modularity features in Java 9 form the main subjects of this book. Each chapter will add to the full picture of Java 9 programming starting out with classes and instances and ending with generics and modularity in Java.
Table of Contents (16 chapters)
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Preface
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Preface
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What this book covers
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What you need for this book
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Who this book is for
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Conventions
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Reader feedback
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Customer support
Lock Free Chapter
1
1. JShell – A Read-Evaluate-Print-Loop for Java 9
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1. JShell – A Read-Evaluate-Print-Loop for Java 9
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Getting ready for our journey toward OOP with Java 9
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Installing the required software on Windows, macOS, or Linux
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Running Java 9 code in JShell
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Working with variables, methods, and sources
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Editing the source code in our favorite external code editor
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Loading source code
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Test your knowledge
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Summary
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2. Real-World Objects to UML Diagrams and Java 9 via JShell
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2. Real-World Objects to UML Diagrams and Java 9 via JShell
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Identifying objects from applications requirements
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Capturing real-world objects
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Generating classes to create objects
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Recognizing variables and constants
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Identifying actions to create methods
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Organizing classes with UML diagrams
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Using feedback from domain experts
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Test your knowledge
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Summary
3
3. Classes and Instances
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3. Classes and Instances
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Understanding classes and instances in Java 9
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Working with object initialization and its customization
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Introducing garbage collection
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Declaring classes
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Customizing constructors and initialization
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Understanding how garbage collection works
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Creating instances of classes and understanding their scope
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Exercises
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Test your knowledge
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Summary
4
4. Encapsulation of Data
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4. Encapsulation of Data
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Understanding members composing a class
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Declaring immutable fields
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Working with setters and getters
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Combining setters, getters, and fields
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Transforming values with setters and getters
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Using static fields to provide class-level values
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Using static methods to provide overridable class-level values
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Test your knowledge
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Summary
5
5. Mutable and Immutable Classes
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5. Mutable and Immutable Classes
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Creating mutable classes in Java 9
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Working with mutable objects in JShell
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Building immutable classes in Java 9
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Working with immutable objects in JShell
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Understanding the differences between mutating and non-mutating objects
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Learning the advantages of non-mutating objects when writing concurrent code
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Working with instances of the immutable String class
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Creating the immutable version of an existing mutable class
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Test your knowledge
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Summary
6
6. Inheritance, Abstraction, Extension, and Specialization
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6. Inheritance, Abstraction, Extension, and Specialization
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Creating class hierarchies to abstract and specialize behavior
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Understanding inheritance
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Creating an abstract base class
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Declaring classes that inherit from another class
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Overriding and overloading methods
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Test your knowledge
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Summary
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7. Members Inheritance and Polymorphism
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7. Members Inheritance and Polymorphism
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Creating concrete classes that inherit from abstract superclasses
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Understanding polymorphism
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Controlling overridability of members in subclasses
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Controlling subclassing of classes
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Creating methods that work with instances of different subclasses
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Test your knowledge
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Summary
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8. Contract Programming with Interfaces
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8. Contract Programming with Interfaces
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Understanding how interfaces work in combination with classes
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Declaring interfaces
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Declaring classes that implement interfaces
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Taking advantage of the multiple inheritance of interfaces
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Combining class inheritance and interfaces
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Test your knowledge
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Summary
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9. Advanced Contract Programming with Interfaces
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9. Advanced Contract Programming with Interfaces
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Working with methods receiving interfaces as arguments
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Downcasting with interfaces and classes
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Treating instances of an interface type as a different subclass
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Taking advantage of default methods in interfaces in Java 9
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Test your knowledge
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Summary
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10. Maximization of Code Reuse with Generics
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10. Maximization of Code Reuse with Generics
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Understanding parametric polymorphism, Java 9 generics, and generic code
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Declaring an interface to be used as a type constraint
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Declaring a class that conforms to multiple interfaces
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Declaring subclasses that inherit the implementation of interfaces
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Creating exception classes
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Declaring a class that works with a constrained generic type
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Using a generic class for multiple compatible types
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Test your knowledge
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Summary
11
11. Advanced Generics
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11. Advanced Generics
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Creating a new interface to be used as a constraint for a second type parameter
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Declaring two classes that implement an interface to work with two type parameters
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Declaring a class that works with two constrained generic types
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Creating instances of a generic class with two generic type parameters
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Test your knowledge
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Summary
12
12. Object-Oriented, Functional Programming, and Lambda Expressions
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12. Object-Oriented, Functional Programming, and Lambda Expressions
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Understanding functions and methods as first-class citizens
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Working with functional interfaces and lambda expressions
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Creating a functional version of array filtering
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Creating a data repository with generics and interfaces
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Filtering collections with complex conditions
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Using a map operation to transform values
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Combining a map operation with reduce
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Chaining many operations with map and reduce
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Working with different collectors
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Test your knowledge
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Summary
13
13. Modularity in Java 9
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13. Modularity in Java 9
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Refactoring existing code to take advantage of object-oriented programming
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Organizing object-oriented code with the new modularity in Java 9
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Creating modular source code
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Compiling multiple modules with the Java 9 compiler
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Run modularized code with Java 9
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Test your knowledge
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Summary
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A. Exercise Answers
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Chapter 1, JShell – A Read-Evaluate-Print-Loop for Java 9
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Chapter 2, Real-World Objects to UML Diagrams and Java 9 via JShell
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Chapter 3, Classes and Instances
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Chapter 4, Encapsulation of Data
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Chapter 5, Mutable and Immutable Classes
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Chapter 6, Inheritance, Abstraction, Extension, and Specialization
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Chapter 7, Members Inheritance and Polymorphism
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Chapter 8, Contract Programming with Interfaces
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Chapter 9, Advanced Contract Programming with Interfaces
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Chapter 10, Maximization of Code Reuse with Generics
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Chapter 11, Advanced Generics
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Chapter 12, Object-Oriented, Functional Programming, and Lambda Expressions
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Chapter 13, Modularity in Java 9
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Index
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Index

Creating a functional version of array filtering

The preceding code that declared the filterNumbersWithFunction method represents an imperative version of array filtering with an external for loop. We can use the filter method available for a Stream<T> object, in this case, a Stream<Integer> object, and achieve the same goal with a functional approach.

The next lines use a functional approach to generate a List<Integer> with the numbers included in the List<Integer> range1to20 that are divisible by 3. The code file for the sample is included in the java_9_oop_chapter_12_01 folder, in the example12_04.java file.

List<Integer> divisibleBy3Numbers2 = range1to20.stream().filter(n -> n % 3 == 0).collect(Collectors.toList());

If we want the previous code to run in JShell, we must enter all the code in a single line, which wouldn't be necessary for the Java compiler to successfully compile the code. It is a specific problem with JShell, streams, and lambda expression...

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