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

Java 9 with JShell

By : Gaston C. Hillar
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Java 9 with JShell

Java 9 with JShell

2 (2)
By: Gaston 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
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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
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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

Understanding classes and instances in Java 9

In the previous chapter, we learned some of the basics of the object-oriented paradigm, including classes and objects. We started working on the backend for a Web Service related to 2D shapes. We ended up creating a UML diagram with the structure of many classes, including their hierarchy, fields, and methods. It is time to take advantage of JShell to start coding a basic class and work with its instances in JShell.

In Java 9, a class is always the type and blueprint. The object is the working instance of the class, and therefore, objects are also known as instances.

Note

Classes are first-class citizens in Java 9 and they will be the main building blocks of our object-oriented solutions.

One or more variables can hold a reference to an instance. For example, consider that we have the following three variables of the Rectangle type:

  • rectangle1
  • rectangle2
  • rectangle10
  • rectangle20

Let's consider that the rectangle1 variable holds a reference to an...

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