Intro to Reactive Programming and RxJava: How to React 😮😱🤪

Approach programming in a new way by using Reactive Programming, a functional style that focuses on the flow and manipulation of data. You already know how to think imperatively, using if-statements and state variables, from your experience programming in C. We will discuss the history of Imperative and Reactive programming and compare the different styles with concrete code examples in Java. By the end of this talk you will understand when to use reactive programming and how powerful and succinct it is for data problems.

Transcript

1. Intro to Reactive Programming and RxJava:
   How to React
   Jordan Jozwiak
   

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2. Reactive
   Programming
   Allows us to manipulate a
   stream of data with functions.

   

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3. Reactive
   Programming
   Allows us to manipulate a
   stream of data with functions.

   (asynchronously)
   

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4. Reactive
   Programming
   

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5. Reactive
   Programming
   1. Data streams

   

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6. Reactive
   Programming
   1. Data streams

   2. Functional Programming

   

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7. Reactive
   Programming
   1. Data streams

   2. Functional Programming

   3. Asynchronous observers
   

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8. applications
   ! Retrieving data from a database and then filtering out some results
   based on user settings.
   

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9. applications
   ! Retrieving data from a database and then filtering out some results
   based on user settings.
   2 3 7
   

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10. applications
    ! Retrieving data from a database and then filtering out some results
    based on user settings.
    ⏳
    

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11. applications
    ! Retrieving data from a database and then filtering out some results
    based on user settings.
    a, b, c -> a, c
    

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12. applications
    ! Retrieve data from a database and then filtering out some results
    based on user settings.
    ! Render a UI that combines data from multiple data sources
    ! Create a real-time model for stock prices
    ! Show auto-complete search results to a user
    ! Log data from a temperature, wind, or pressure sensor
    

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13. Who actually uses this?
    

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14. Who actually uses this?
    ! Very popular in the Android community
    

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15. Who actually uses this?
    ! Very popular in the Android community
    ! Some usage at Google for database requests
    

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16. Who actually uses this?
    ! Very popular in the Android community
    ! Some usage at Google for database requests
    ! Microsoft, Netflix, GitHub, SoundCloud, and more (see reactivex.io)
    

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17. Reactive Programming
    Theory
    

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18. Reactive Programming
    Theory
    Implementation
    Reactive Extensions (reactivex.io)
    (libraries to make normal languages reactive)
    

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19. Reactive Programming
    Theory
    Implementation
    Reactive Extensions (reactivex.io)
    (libraries to make normal languages reactive)
    RxJava RxSwift RxJS …
    

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21. 4 2 1 7 6
    

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22. 4 2 1 7 6
    filter(x -> (x % 2) == 0)
    

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23. 4 2 1 7 6
    filter(x -> (x % 2) == 0)
    

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24. 4 2 1 7 6
    filter(x -> (x % 2) == 0)
    4
    

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25. 4 2 1 7 6
    filter(x -> (x % 2) == 0)
    4 2
    

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26. 4 2 1 7 6
    filter(x -> (x % 2) == 0)
    4 2 6
    

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27. 4 2 1 7 6
    filter(x -> (x % 2) == 0)
    4 2 6
    
    

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28. 4 2 1 7 6
    SUBJECT
    subject - the stream that emits data
    4 2 6
    

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29. 4 2 6
    OBSERVER
    observer - “subscribes to” or “consumes” data. There
    can be multiple observers for a single subject.
    4 2 1 7 6
    

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30. 4 2 1 7 6
    filter(x -> (x % 2) == 0)
    4 2 6
    SUBJECT
    OBSERVER
    

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31. 4 2 1 7 6
    filter(x -> (x % 2) == 0)
    4 2 6
    SUBJECT
    OBSERVER
    4 2 6
    SERVER 2
    

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32. 4 2 1 7 6
    filter / map / count / 

    max / min / delay / ...
    SUBJECT
    OBSERVER
    

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33. 4 2 1 7 6
    some function that takes ⏳
    SUBJECT
    OBSERVER
    

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34. 4 2 1 7 6
    some function that takes ⏳
    SUBJECT
    OBSERVER
    

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35. a d z a h
    some function that takes ⏳
    SUBJECT
    OBSERVER
    

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36. some function that takes ⏳
    SUBJECT
    OBSERVER
    

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37. ? ? ? ? ?
    some function that takes ⏳
    ? ? ? ?
    SUBJECT
    OBSERVER
    

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38. some function that takes ⏳
    SUBJECT
    OBSERVER
    another function
    

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39. ? ? ? ? ?
    some function that takes ⏳
    ? ? ? ?
    SUBJECT
    OBSERVER
    another function
    ? ? ? ? ?
    

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40. What creates the subject data stream?
    

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41. What creates the subject data stream?
    ! These streams are called Observables in RxJava
    

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42. What creates the subject data stream?
    ! These streams are called Observables in RxJava
    ! Observable.create(), fromIterable(), etc.
    

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43. What creates the subject data stream?
    ! These streams are called Observables in RxJava
    ! Observable.create(), fromIterable(), etc.
    ! Retrofitting existing object-oriented design into Observable data
    streams can be messy
    

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44. What creates the subject data stream?
    ! These streams are called Observables in RxJava
    ! Observable.create(), fromIterable(), etc.
    ! Retrofitting existing object-oriented design into Observable data
    streams can be messy
    ! Many, many open-source projects that wrap other implementations into
    an Rx package (an easy way to get ⭐ ⭐ ⭐ on GitHub)
    

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45. What creates the subject data stream?
    ! These streams are called Observables in RxJava
    ! Observable.create(), fromIterable(), etc.
    ! Retrofitting existing object-oriented design into Observable data
    streams can be messy
    ! Many, many open-source projects that wrap other implementations into
    an Rx package (an easy way to get ⭐ ⭐ ⭐ on GitHub)
    ! github.com/zsoltk/RxAndroidLibs - 500 stars for a list of libraries
    

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46. introduction
    background
    examples
    live demo
    wrap-up
    

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47. What languages
    are you familiar with?
    

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48. ~80 %
    Percent of the most popular languages are imperative 

    or multi-paradigmatic languages
    Source: StackOverflow Developer Survey 2018
    

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49. What's a language paradigm?
    

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50. What's a language paradigm?
    ! Computer languages resemble linguistic language
    

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51. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    

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52. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    ○ Tenses: past, present, future
    

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53. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    ○ Tenses: past, present, future
    ○ Vocabulary
    

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54. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    ○ Tenses: past, present, future
    ○ Vocabulary
    ○ Dialects
    

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55. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    ○ Tenses: past, present, future
    ○ Vocabulary
    ○ Dialects
    ! Languages are multi-faceted and evolve over time. They are often multi-
    paradigmatic languages.
    

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56. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    ○ Tenses: past, present, future
    ○ Vocabulary
    ○ Dialects
    ! Languages are multi-faceted and evolve over time. They are often multi-
    paradigmatic languages.
    ! Examples
    

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57. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    ○ Tenses: past, present, future
    ○ Vocabulary
    ○ Dialects
    ! Languages are multi-faceted and evolve over time. They are often multi-
    paradigmatic languages.
    ! Examples
    ○ Imperative (what you’re probably used to)
    

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58. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    ○ Tenses: past, present, future
    ○ Vocabulary
    ○ Dialects
    ! Languages are multi-faceted and evolve over time. They are often multi-
    paradigmatic languages.
    ! Examples
    ○ Imperative (what you’re probably used to)
    ○ Reactive Programming (what we’re talking about today)
    

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59. What's a language paradigm?
    ! Computer languages resemble linguistic language
    ○ Grammatical structures
    ○ Tenses: past, present, future
    ○ Vocabulary
    ○ Dialects
    ! Languages are multi-faceted and evolve over time. They are often multi-
    paradigmatic languages.
    ! Examples
    ○ Imperative (what you’re probably used to)
    ○ Reactive Programming (what we’re talking about today)
    ○ Functional Programming (used in Reactive Programming)
    

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60. Imperative vs. Functional
    

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61. Imperative vs. Functional
    Imperative Programming
    

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62. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    

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63. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    

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64. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    

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65. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    

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66. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    

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67. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    if (value % 2 == 0) {
    // do something
    }
    

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68. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    Functional Programming
    if (value % 2 == 0) {
    // do something
    }
    

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69. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    Functional Programming
    ! Describes what the program
    should accomplish
    if (value % 2 == 0) {
    // do something
    }
    

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70. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    Functional Programming
    ! Describes what the program
    should accomplish
    ! Ideally stateless
    if (value % 2 == 0) {
    // do something
    }
    

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71. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    Functional Programming
    ! Describes what the program
    should accomplish
    ! Ideally stateless
    ! Evaluate functions and create
    expressions instead of
    statements
    if (value % 2 == 0) {
    // do something
    }
    

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72. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    Functional Programming
    ! Describes what the program
    should accomplish
    ! Ideally stateless
    ! Evaluate functions and create
    expressions instead of
    statements
    ! More difficult conceptually
    if (value % 2 == 0) {
    // do something
    }
    

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73. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    Functional Programming
    ! Describes what the program
    should accomplish
    ! Ideally stateless
    ! Evaluate functions and create
    expressions instead of
    statements
    ! More difficult conceptually
    ! Examples: Scala, Haskell
    if (value % 2 == 0) {
    // do something
    }
    

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74. Imperative vs. Functional
    Imperative Programming
    ! Describes how the program
    operates
    ! Uses statements to change
    state of the program
    ! Conditional statements, loops,
    inheritance
    ! Easier initial learning curve
    ! Examples: C, PHP, Java
    Functional Programming
    ! Describes what the program
    should accomplish
    ! Ideally stateless
    ! Evaluate functions and create
    expressions instead of
    statements
    ! More difficult conceptually
    ! Examples: Scala, Haskell
    if (value % 2 == 0) {
    // do something
    }
    boolean filter(int value) {
    return value % 2 == 0;
    }
    

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75. History of Imperative Programming
    ! Old computers utilized vacuum tubes and very limited memory
    ! Programs written as step-by-step instructions
    ! FORTRAN introduced in 1954. Compiled, variables, complex
    expressions.
    ! 60s and 70s: COBOL, BASIC, C
    ! Object-oriented code grew in popularity in the 1980s. Smalltalk. C++
    ! 90s: Perl, Python, Javascript, Ruby, Java
    

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76. History of Functional Programming
    ! Based on lambda calculus (Church 1936)
    ○ Study of computation with functions
    ! Lisp was developed by IBM in the 1950s
    ○ LISP = LISt Processor
    ○ Still in use today
    ○ Only a year younger than FORTRAN
    ! John Backus gave a 1978 Turing Award lecture on why imperative programming is
    “bad” and functional programming is “good”
    ! 80s-00s - Object-Oriented programming dominated based on principles like
    encapsulation. Academics and theoreticians care about Functional Programming.
    ! 2010s - JavaScript made passing around functions cool again
    

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77. Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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78. Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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79. A flow of data objects from one
    function to the next
    Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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80. Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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81. ! Functions are meant to be pure
    Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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82. ! Functions are meant to be pure
    ! All functions have an input and
    output data types
    Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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83. ! Functions are meant to be pure
    ! All functions have an input and
    output data types
    ! No external state is modified
    (no side-effects)
    Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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84. ! Functions are meant to be pure
    ! All functions have an input and
    output data types
    ! No external state is modified
    (no side-effects)
    Example:

    add(x, y) -> return x + y
    Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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85. Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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86. Uses the Observer pattern with
    Subject data sources that notify
    Observers
    Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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87. Uses the Observer pattern with
    Subject data sources that notify
    Observers
    Errors propagated through the flow
    of data
    Reactive Programming

    1. Data streams

    

    2. Functional programming

    

    3. Asynchronous observers

    

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88. Reactive Programming is NOT
    

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89. Reactive Programming is NOT
    ! It's own language
    ! React, ReactJs, ReactNative
    

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90. RxJava
    

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91. RxJava
    ! The Java library for the Reactive Extensions specification
    ○ This specification is applied to other languages: RxJs, RxSwift,
    etc. - reactivex.io/languages
    

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92. RxJava
    ! The Java library for the Reactive Extensions specification
    ○ This specification is applied to other languages: RxJs, RxSwift,
    etc. - reactivex.io/languages
    ! Helpful due to complicated stream and asynchronous apis
    

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93. RxJava
    ! The Java library for the Reactive Extensions specification
    ○ This specification is applied to other languages: RxJs, RxSwift,
    etc. - reactivex.io/languages
    ! Helpful due to complicated stream and asynchronous apis
    ! Brings functional design to an object-oriented language
    

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94. RxJava
    ! The Java library for the Reactive Extensions specification
    ○ This specification is applied to other languages: RxJs, RxSwift,
    etc. - reactivex.io/languages
    ! Helpful due to complicated stream and asynchronous apis
    ! Brings functional design to an object-oriented language
    ! Very helpful for mobile development, which often involves
    asynchronously requesting data from a server, transforming it, and
    displaying it in the UI
    

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95. introduction
    background
    examples
    live demo
    wrap-up
    

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96. ... to subscribe to data
    Imperative
    List data = 

    new DataSource().getData();
    for (Integer value : data) {
    System.out.println(value);
    }
    Output: 4, 2, 1, 7, 6, ...
    Data: 4, 2, 1, 7, 6, ...
    

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97. ... to subscribe to data
    Imperative
    List data = 

    new DataSource().getData();
    for (Integer value : data) {
    System.out.println(value);
    }
    Output: 4, 2, 1, 7, 6, ...
    Data: 4, 2, 1, 7, 6, ...
    

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98. ... to subscribe to data
    Imperative
    List data = 

    new DataSource().getData();
    for (Integer value : data) {
    System.out.println(value);
    }
    Output: 4, 2, 1, 7, 6, ...
    Data: 4, 2, 1, 7, 6, ...
    

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99. ... to subscribe to data
    Reactive
    new DataSource().getDataStream()
    .subscribe(new Consumer() {
    @Override
    public void accept(Integer value) {
    System.out.println(value);
    }
    });
    Imperative
    List data = 

    new DataSource().getData();
    for (Integer value : data) {
    System.out.println(value);
    }
    Output: 4, 2, 1, 7, 6, ...
    Data: 4, 2, 1, 7, 6, ...
    

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100. ... to subscribe to data
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     Reactive
     new DataSource().getDataStream()
     .subscribe(new Consumer() {
     @Override
     public void accept(Integer value) {
     System.out.println(value);
     }
     });
     Output: 4, 2, 1, 7, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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101. ... to subscribe to data
     Reactive
     new DataSource().getDataStream()
     .subscribe(new Consumer() {
     @Override
     public void accept(Integer value) {
     System.out.println(value);
     }
     });
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     Output: 4, 2, 1, 7, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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102. ... to subscribe to data
     Reactive
     new DataSource().getDataStream()
     .subscribe(new Consumer() {
     @Override
     public void accept(Integer value) {
     System.out.println(value);
     }
     });
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     Output: 4, 2, 1, 7, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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103. ... to subscribe to data
     Reactive
     new DataSource().getDataStream()
     .subscribe(new Consumer() {
     @Override
     public void accept(Integer value) {
     System.out.println(value);
     }
     });
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     Output: 4, 2, 1, 7, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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104. ... to subscribe to data
     Reactive
     new DataSource().getDataStream()
     .subscribe(new Consumer() {
     @Override
     public void accept(Integer value) {
     System.out.println(value);
     }
     });
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     Output: 4, 2, 1, 7, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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105. ... to subscribe to data
     Reactive
     new DataSource().getDataStream()
     .subscribe(

     value -> System.out.println(value)

     );
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     Output: 4, 2, 1, 7, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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106. ... to subscribe to data
     Reactive
     new DataSource().getDataStream()
     .subscribe(
     value -> System.out.println(value)
     );
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     Output: 4, 2, 1, 7, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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107. ... to subscribe to data
     Reactive
     new DataSource().getDataStream()
     .subscribe(
     value -> updateUI(value)
     );
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     updateUI(value);
     }
     

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108. ... to subscribe to data
     Reactive
     new DataSource().getDataStream()
     .subscribe(
     value -> saveToDatabase(value)
     );
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     saveToDatabase(value);
     }
     

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109. ... to subscribe to data changes
     

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110. ... to subscribe to data changes
     Imperative
     ScheduledExecutorService scheduler = // initialize
     Runnable runner = new Runnable() {
     public void run() {
     List data = new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     }
     };
     ScheduledFuture> future = // initialize
     scheduler.schedule(new Runnable() {
     public void run() {
     future.cancel(/* mayInterruptIfRunning */ true);
     }
     }, /* delay */ 0, TimeUnit.SECONDS);
     

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111. ... to subscribe to data changes
     Imperative
     ScheduledExecutorService scheduler = // initialize
     Runnable runner = new Runnable() {
     public void run() {
     List data = new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     }
     };
     ScheduledFuture> future = // initialize
     scheduler.schedule(new Runnable() {
     public void run() {
     future.cancel(/* mayInterruptIfRunning */ true);
     }
     }, /* delay */ 0, TimeUnit.SECONDS);
     ???
     

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112. ... to subscribe to data changes
     Imperative
     ScheduledExecutorService scheduler = // initialize
     Runnable runner = new Runnable() {
     public void run() {
     List data = new DataSource().getData();
     for (Integer value : data) {
     System.out.println(value);
     }
     }
     };
     ScheduledFuture> future = // initialize
     scheduler.schedule(new Runnable() {
     public void run() {
     future.cancel(/* mayInterruptIfRunning */ true);
     }
     }, /* delay */ 0, TimeUnit.SECONDS);
     Reactive
     new DataSource().getDataStream()
     .subscribe(
     value -> System.out.println(value)
     );
     

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113. ... to filter our data
     

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114. ... to filter our data
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     if (value % 2 == 0) {
     System.out.println(value);
     }
     }
     Output: 4, 2, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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115. ... to filter our data
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     if (value % 2 == 0) {
     System.out.println(value);
     }
     }
     Output: 4, 2, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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116. ... to filter our data
     http://reactivex.io/documentation/operators/filter
     

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117. ... to filter our data
     Reactive
     new DataSource().getDataStream()
     .filter(value -> value % 2 == 0)
     .subscribe(

     result -> System.out.println(result)

     );
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     if (value % 2 == 0) {
     System.out.println(value);
     }
     }
     Output: 4, 2, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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118. ... to filter our data
     Reactive
     new DataSource().getDataStream()
     .filter(value -> value % 2 == 0)
     .subscribe(

     result -> System.out.println(result)

     );
     Imperative
     List data = 

     new DataSource().getData();
     for (Integer value : data) {
     if (value % 2 == 0) {
     System.out.println(value);
     }
     }
     Output: 4, 2, 6, ...
     Data: 4, 2, 1, 7, 6, ...
     

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119. … to map our data
     Output: 8, 4, 2, 14, 12, ...
     Data: 4, 2, 1, 7, 6, ...
     

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120. … to map our data
     Imperative
     List data =
     new DataSource().getData();
     for (Integer value : data) {
     int result = value * 2;
     System.out.println(result);
     }
     Output: 8, 4, 2, 14, 12, ...
     Data: 4, 2, 1, 7, 6, ...
     

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121. ... to map our data
     Imperative
     List data =
     new DataSource().getData();
     for (Integer value : data) {
     int result = value * 2;
     System.out.println(result);
     }
     Output: 8, 4, 2, 14, 12, ...
     Data: 4, 2, 1, 7, 6, ...
     

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122. ... to map our data
     http://reactivex.io/documentation/operators/map
     

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123. ... to map our data
     Reactive
     new DataSource().getDataStream()
     .map(value -> value * 2)
     .subscribe(
     result -> System.out.println(result)
     );
     Imperative
     List data =
     new DataSource().getData();
     for (Integer value : data) {
     int result = value * 2;
     System.out.println(result);
     }
     Output: 8, 4, 2, 14, 12, ...
     Data: 4, 2, 1, 7, 6, ...
     

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124. ... to map our data
     Reactive
     new DataSource().getDataStream()
     .map(value -> value * 2)
     .subscribe(
     result -> System.out.println(result)
     );
     Imperative
     List data =
     new DataSource().getData();
     for (Integer value : data) {
     int result = value * 2;
     System.out.println(result);
     }
     Output: 8, 4, 2, 14, 12, ...
     Data: 4, 2, 1, 7, 6, ...
     

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125. ... to group our data
     

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126. ... to group our data
     List data =
     new DataSource().getData();
     Map> result =
     new HashMap<>();
     String evenKey = "EVEN";
     String oddKey = "ODD";
     for (Integer value : data) {
     String key;
     if (value % 2 == 0) {
     key = evenKey;
     } else {
     key = oddKey;
     }
     result.putIfAbsent(
     key,
     new ArrayList<>());
     result.get(key).add(datum);
     }
     System.out.println(result);
     Output: {EVEN=[4, 2, 6], ODD=[1, 7]}
     Data: 4, 2, 1, 7, 6
     

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127. ... to group our data
     http://reactivex.io/documentation/operators/groupby
     

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128. ... to group our data
     new DataSource().getDataStream()
     .groupBy(
     value -> (value % 2) == 0 ? "EVEN" : "ODD"
     )
     .collectInto(
     // put our groups into a hashmap
     // this is actually still a little messy
     )
     .subscribe(
     resultMap -> System.out.println(resultMap)
     );
     Output: {EVEN=[4, 2, 6], ODD=[1, 7]}
     Data: 4, 2, 1, 7, 6
     

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129. ... to group our data
     new DataSource().getDataStream()
     .groupBy(
     value -> (value % 2) == 0 ? "EVEN" : "ODD"
     )
     .collectInto(
     // put our groups into a hashmap
     // this is actually still a little messy
     )
     .subscribe(
     resultMap -> System.out.println(resultMap)
     );
     List data =
     new DataSource().getData();
     Map> result =
     new HashMap<>();
     String evenKey = "EVEN";
     String oddKey = "ODD";
     for (Integer value : data) {
     String key;
     if (value % 2 == 0) {
     key = evenKey;
     } else {
     key = oddKey;
     }
     result.putIfAbsent(
     key,
     new ArrayList<>());
     result.get(key).add(datum);
     }
     System.out.println(result);
     Output: {EVEN=[4, 2, 6], ODD=[1, 7]}
     Data: 4, 2, 1, 7, 6
     

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130. So many more operators
     ! Transforming
     ! Buffer
     ! Scan
     ! Filtering
     ! Debounce
     ! Distinct
     ! First
     ! Last
     ! Take
     ! Min
     ! Combining
     ! Join
     ! Merge
     ! Zip
     ! Math
     ! Average
     ! Concat
     ! Max
     

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131. Some operations can get complicated
     http://reactivex.io/documentation/operators/join
     

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132. introduction
     background
     examples
     live demo
     wrap-up
     

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133. introduction
     background
     examples
     live demo
     wrap-up
     

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134. Reactive
     Programming
     1. Data streams

     2. Functional Programming

     3. Asynchronous observers
     

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135. Thanks!
     
     

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