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  • Book Overview & Buying Programming Kotlin
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Programming Kotlin

Programming Kotlin

By : Samuel, Bocutiu
3.4 (7)
Buy this Book
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Programming Kotlin

Programming Kotlin

3.4 (7)
By: Samuel, Bocutiu
Buy this Book

Overview of this book

Quickly learn the fundamentals of the Kotlin language and see it in action on the web. Easy to follow and covering the full set of programming features, this book will get you fluent in Kotlin for Android.
Table of Contents (14 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
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1
1. Getting Started with Kotlin
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1. Getting Started with Kotlin
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Using the command line to compile and run Kotlin code
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Kotlin runtime
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The REPL
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Kotlin for scripting
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Kotlin with Gradle
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Kotlin with Maven
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IntelliJ and Kotlin
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Eclipse and Kotlin
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Mixing Kotlin and Java in a project
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Summary
2
2. Kotlin Basics
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2. Kotlin Basics
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Vals and vars
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Type inference
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Basic types
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Comments
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Packages
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Imports
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String templates
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Ranges
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Loops
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Exception handling
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Instantiating classes
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Referential equality and structural equality
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This expression
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Visibility modifiers
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Control flow as expressions
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Null syntax
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When expression
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Type hierarchy
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Summary
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3. Object-Oriented Programming in Kotlin
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3. Object-Oriented Programming in Kotlin
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Classes
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Interfaces
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Inheritance
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Visibility modifiers
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Abstract classes
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Interface or abstract class
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Polymorphism
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Overriding rules
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Inheritance versus composition
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Class delegation
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Sealed classes
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Summary
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4. Functions in Kotlin
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4. Functions in Kotlin
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Defining functions
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Single expression functions
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Member functions
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Local functions
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Top-level functions
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Named parameters
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Default parameters
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Extension functions
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Operators
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Function literals
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Tail recursive functions
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Varargs
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Standard library functions
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Generic functions
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Pure functions
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Java from Kotlin
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Kotlin from Java
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Summary
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5. Higher Order Functions and Functional Programming
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5. Higher Order Functions and Functional Programming
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Higher order functions
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Closures
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Anonymous functions
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Function references
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Function-literal receivers
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Functions in the JVM
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Function composition
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Inline functions
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Currying and partial application
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Memoization
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Type alias
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Either
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Custom DSLs
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Validation and error accumulation
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Summary
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6. Properties
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6. Properties
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Why use properties?
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Syntax and variations
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Visibility
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Late initialization
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Delegated properties
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Lazy initializations
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Lateinit versus lazy
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Observables
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A non-null property delegate
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Properties or methods?
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Summary
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7. Null Safety, Reflection, and Annotations
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7. Null Safety, Reflection, and Annotations
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Nullable types
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Smart cast
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Safe null access
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Elvis operator
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Safe casting
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Optionals
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Reflection
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Constructors
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Objects and companions
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Useful KClass properties
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Reflective functions and properties
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Annotations
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Standard annotations
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Runtime annotation discovery
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Summary
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8. Generics
chevron up
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8. Generics
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Parameterised functions
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Parameterized types
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Bounded polymorphism
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Type variance
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Nothing type
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Type projection
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Type erasure
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Type reification
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Recursive type bounds
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Algebraic data types
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Summary
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9. Data Classes
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9. Data Classes
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Automatic creation of getters and setters
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The copy method
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toString out of the box
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hashCode and equals methods generated for you
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Destructed declarations
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Destructing types
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Data class definition rules
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Limitations
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Summary
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10. Collections
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10. Collections
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Class hierarchy
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Arrays
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Lists
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Maps
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Sets
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Read-only views
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Indexed access
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Sequences
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Summary
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11. Testing in Kotlin
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11. Testing in Kotlin
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Getting started
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Choosing a spec
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Matchers
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Inspectors
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Interceptors
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Project config
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Property testing
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Table-driven testing
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Tags, conditions, and config
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Summary
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12. Microservices with Kotlin
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12. Microservices with Kotlin
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Definition
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Drawbacks
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Why microservices?
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Lagom
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Defining services
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Implementing a Lagom service
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Summary
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13. Concurrency
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13. Concurrency
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Threads
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Deadlocks and livelocks
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Executors
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Race conditions
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Summary

Type projection

In the Type variance section, we worked through examples of covariance and contravariance, and how each of these restricts type parameters to be used as input types or return types respectively. This is usually not an issue when we are defining our own interfaces and classes as we can come up with the correct abstractions required.

But what about the case where someone else has defined a class to be invariant and you require it to be used in a covariant or contravariant way? Kotlin addresses this by introducing a powerful addition called type projections.

When using type parameters, there is a distinction between use site and declaration site variance. Use site variance is the term used when the variance of type parameters is set by the variable itself, as in Java. Declaration site variance is the term used when the type or function determines the variance, as in Kotlin.

Type projections allow us to specify variance at the use site instead. Let's revisit our earlier example...

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