11. Advanced Generics | Java 9 with JShell

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Table Of Contents

Java 9 with JShell

By : Gastón C. Hillar

2 (2)

Java 9 with JShell

2 (2)

By: Gastón C. Hillar

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.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. JShell – A Read-Evaluate-Print-Loop for Java 9

1. JShell – A Read-Evaluate-Print-Loop for Java 9

Getting ready for our journey toward OOP with Java 9

Installing the required software on Windows, macOS, or Linux

Running Java 9 code in JShell

Working with variables, methods, and sources

Editing the source code in our favorite external code editor

Loading source code

Test your knowledge

Summary

2. Real-World Objects to UML Diagrams and Java 9 via JShell

2. Real-World Objects to UML Diagrams and Java 9 via JShell

Identifying objects from applications requirements

Capturing real-world objects

Generating classes to create objects

Recognizing variables and constants

Identifying actions to create methods

Organizing classes with UML diagrams

Using feedback from domain experts

Test your knowledge

Summary

3. Classes and Instances

3. Classes and Instances

Understanding classes and instances in Java 9

Working with object initialization and its customization

Introducing garbage collection

Declaring classes

Customizing constructors and initialization

Understanding how garbage collection works

Creating instances of classes and understanding their scope

Exercises

Test your knowledge

Summary

4. Encapsulation of Data

4. Encapsulation of Data

Understanding members composing a class

Declaring immutable fields

Working with setters and getters

Combining setters, getters, and fields

Transforming values with setters and getters

Using static fields to provide class-level values

Using static methods to provide overridable class-level values

Test your knowledge

Summary

5. Mutable and Immutable Classes

5. Mutable and Immutable Classes

Creating mutable classes in Java 9

Working with mutable objects in JShell

Building immutable classes in Java 9

Working with immutable objects in JShell

Understanding the differences between mutating and non-mutating objects

Learning the advantages of non-mutating objects when writing concurrent code

Working with instances of the immutable String class

Creating the immutable version of an existing mutable class

Test your knowledge

Summary

6. Inheritance, Abstraction, Extension, and Specialization

6. Inheritance, Abstraction, Extension, and Specialization

Creating class hierarchies to abstract and specialize behavior

Understanding inheritance

Creating an abstract base class

Declaring classes that inherit from another class

Overriding and overloading methods

Test your knowledge

Summary

7. Members Inheritance and Polymorphism

7. Members Inheritance and Polymorphism

Creating concrete classes that inherit from abstract superclasses

Understanding polymorphism

Controlling overridability of members in subclasses

Controlling subclassing of classes

Creating methods that work with instances of different subclasses

Test your knowledge

Summary

8. Contract Programming with Interfaces

8. Contract Programming with Interfaces

Understanding how interfaces work in combination with classes

Declaring interfaces

Declaring classes that implement interfaces

Taking advantage of the multiple inheritance of interfaces

Combining class inheritance and interfaces

Test your knowledge

Summary

9. Advanced Contract Programming with Interfaces

9. Advanced Contract Programming with Interfaces

Working with methods receiving interfaces as arguments

Downcasting with interfaces and classes

Treating instances of an interface type as a different subclass

Taking advantage of default methods in interfaces in Java 9

Test your knowledge

Summary

10. Maximization of Code Reuse with Generics

10. Maximization of Code Reuse with Generics

Understanding parametric polymorphism, Java 9 generics, and generic code

Declaring an interface to be used as a type constraint

Declaring a class that conforms to multiple interfaces

Declaring subclasses that inherit the implementation of interfaces

Creating exception classes

Declaring a class that works with a constrained generic type

Using a generic class for multiple compatible types

Test your knowledge

Summary

11. Advanced Generics

11. Advanced Generics

Creating a new interface to be used as a constraint for a second type parameter

Declaring two classes that implement an interface to work with two type parameters

Declaring a class that works with two constrained generic types

Creating instances of a generic class with two generic type parameters

Test your knowledge

Summary

12. Object-Oriented, Functional Programming, and Lambda Expressions

12. Object-Oriented, Functional Programming, and Lambda Expressions

Understanding functions and methods as first-class citizens

Working with functional interfaces and lambda expressions

Creating a functional version of array filtering

Creating a data repository with generics and interfaces

Filtering collections with complex conditions

Using a map operation to transform values

Combining a map operation with reduce

Chaining many operations with map and reduce

Working with different collectors

Test your knowledge

Summary

13. Modularity in Java 9

13. Modularity in Java 9

Refactoring existing code to take advantage of object-oriented programming

Organizing object-oriented code with the new modularity in Java 9

Creating modular source code

Compiling multiple modules with the Java 9 compiler

Run modularized code with Java 9

Test your knowledge

Summary

A. Exercise Answers

Chapter 1, JShell – A Read-Evaluate-Print-Loop for Java 9

Chapter 2, Real-World Objects to UML Diagrams and Java 9 via JShell

Chapter 3, Classes and Instances

Chapter 4, Encapsulation of Data

Chapter 5, Mutable and Immutable Classes

Chapter 6, Inheritance, Abstraction, Extension, and Specialization

Chapter 7, Members Inheritance and Polymorphism

Chapter 8, Contract Programming with Interfaces

Chapter 9, Advanced Contract Programming with Interfaces

Chapter 10, Maximization of Code Reuse with Generics

Chapter 11, Advanced Generics

Chapter 12, Object-Oriented, Functional Programming, and Lambda Expressions

Chapter 13, Modularity in Java 9

Index

Index

Creating instances of a generic class with two generic type parameters

We can create instances of the PartyWithHearable<T, U> class by replacing both the T and U generic type parameters with any type names that conform to the constraints or the upper bounds specified in the declaration of the PartyWithHearable<T, U> class. We have three concrete classes that implement both the Sociable and Comparable<Sociable> interfaces required by the T generic type parameter: SocialLion, SocialParrot, and SocialSwan. We have two classes that implement the Hearable interface required by the U generic type parameter: Smartphone and AnimalMusicBand.

We can use SocialLion and Smartphone to create an instance of PartyWithHearable<SocialLion, Smartphone>, that is, a party of social lions and a smartphone. Then, we can use SocialParrot and AnimalMusicBand to create an instance of PartyWithHearable<SocialParrot, AnimalMusicBand>, that is, a party of social parrots and an animal music...

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