Java 8 on Android

Video: https://skillsmatter.com/skillscasts/8696-java-8-on-android

Java 8 features have finally made their way to the Android world and if you haven't been trying them, you are missing out. This talk is all about getting you up to speed on all of these new features and how to use them. It will be a great primer if you've never looked into them or a refresher if it's been a while.

Transcript

1. Java 8 on Android
   Alex Florescu
   YPlan
   @flor3scu
   

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2. Outline
   • Backward compatible features
   • Lambdas, method references etc.
   • Android N+ only features
   • Streams, default methods etc.
   • Setup: how to get this working
   • Other useful tidbits and analysis
   

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3. Notes
   • Slides are online
   • All code is online
   

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4. Backward-compatible
   features
   • Lambdas
   • Method references
   • Type annotations
   

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5. API support
   • Official website

   “Also available on API level 23 and lower”
   • Google I/O 2016

   “Backward compatible with Gingerbread”
   

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6. Backward-compatible
   features
   • Lambdas
   • Method references
   • Type annotations
   

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7. Lambdas
   & Method references
   

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8. Functional interface
   • Has exactly one abstract method
   • Can annotate with @FunctionalInterface
   • Not necessary for using lambdas with it
   

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9. OnClickListener
   public interface OnClickListener {

   void onClick(View v);

   }
   

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10. Functional interface
    • A lot of standard ones added in java.util.function
    • Consumer — an operation that accepts a single
    input argument and returns no result
    • Function — a function that accepts one
    argument and produces a result
    • Predicate — a predicate (boolean-valued function)
    of one argument
    • Supplier — a supplier of results
    

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11. Lambdas
    & Method references
    

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12. Lambdas
    Language construct that simplifies (or flattens)
    anonymous inner classes
    

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13. Setting listener
    button1.setOnClickListener(new View.OnClickListener() {

    @Override public void onClick(View v) {

    Snackbar.make(mainPanel, "Click listener

    triggered", Snackbar.LENGTH_SHORT).show();

    }

    });
    

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14. Setting listener
    button1.setOnClickListener(new View.OnClickListener() {

    @Override public void onClick(View v) {

    Snackbar.make(mainPanel, "Click listener

    triggered", Snackbar.LENGTH_SHORT).show();

    }

    });
    

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15. Setting listener
    button1.setOnClickListener(v -> 

    Snackbar.make(mainPanel, "Click listener triggered", 

    Snackbar.LENGTH_SHORT).show());
    

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16. Setting listener
    button1.setOnClickListener(v -> 

    Snackbar.make(mainPanel, "Click listener triggered", 

    Snackbar.LENGTH_SHORT).show());
    

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17. Lambda examples
    // Lambda with no parameters

    Runnable r2 = () -> Timber.d("Lambda test");
    

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18. Example with params
    participantRedList.setAdapter(

    new ParticipantAdapter(

    

    filterParticipants(participants,

    new FilterCondition() {

    @Override

    public boolean accept(Participant candidate) {

    return candidate.getTeamColour() ==
    TeamColour.RED;

    }

    })));
    

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19. Example with params
    participantRedList.setAdapter(

    new ParticipantAdapter(

    

    filterParticipants(participants,

    new FilterCondition() {

    @Override

    public boolean accept(Participant candidate) {

    return candidate.getTeamColour() ==
    TeamColour.RED;

    }

    })));
    

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20. Example with params
    participantRedList.setAdapter(

    new ParticipantAdapter(

    

    filterParticipants(participants,

    new FilterCondition() {

    @Override

    public boolean accept(Participant candidate) {

    return candidate.getTeamColour() ==
    TeamColour.RED;

    }

    })));
    

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21. Example with params
    participantRedList.setAdapter(

    new ParticipantAdapter(

    filterParticipants(participants,

    (candidate) -> candidate.getTeamColour() ==
    TeamColour.RED)));
    

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22. Example with params
    participantRedList.setAdapter(

    new ParticipantAdapter(

    filterParticipants(participants,

    (candidate) -> candidate.getTeamColour() ==
    TeamColour.RED)));
    

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23. Syntax
    p -> p.getAge() >= 18
    (a,b) -> a.getAge() < b.getAge()
    () -> Timber.d(“Ping”)
    (p) -> {

    Timber.d(“Participant age : %d”, p.getAge());

    return p.getAge() < 18;

    }
    

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24. Syntax
    p -> p.getAge() >= 18
    (a,b) -> a.getAge() < b.getAge()
    () -> Timber.d(“Ping”)
    (p) -> {

    Timber.d(“Participant age : %d”, p.getAge());

    return p.getAge() < 18;

    }
    

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25. Syntax
    p -> p.getAge() >= 18
    (a,b) -> a.getAge() < b.getAge()
    () -> Timber.d(“Ping”)
    (p) -> {

    Timber.d(“Participant age : %d”, p.getAge());

    return p.getAge() < 18;

    }
    

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26. Syntax
    p -> p.getAge() >= 18
    (a,b) -> a.getAge() < b.getAge()
    () -> Timber.d(“Ping”)
    (p) -> {

    Timber.d(“Participant age : %d”, p.getAge());

    return p.getAge() < 18;

    }
    

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27. Lambdas
    & Method references
    

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28. Method references
    Compact lambda expressions for methods that already
    have a name
    

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29. Example
    

    Collections.sort(participants,
    new Comparator() {

    @Override

    public int compare(Participant p1, Participant p2) {

    return Integer.compare(p1.getAge(), 

    p2.getAge());

    }

    });
    

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30. Example
    

    Collections.sort(participants,
    (p1, p2) -> Integer.compare(p1.getAge(), 

    p2.getAge()));
    

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31. Example
    public final class Participant {

    ….

    public static int compareByAge(Participant a, 

    Participant b) {

    return Integer.compare(a.getAge(), b.getAge());

    }

    ….

    }
    

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32. Example
    public final class Participant {

    ….

    public static int compareByAge(Participant a, 

    Participant b) {

    return Integer.compare(a.getAge(), b.getAge());

    }

    ….

    }
    

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33. Example
    

    Collections.sort(participants,
    new Comparator() {

    @Override

    public int compare(Participant p1, Participant p2) {

    return Participant.compareByAge(p1,p2);

    }

    });
    

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34. Example
    

    Collections.sort(participants,
    (p1, p2) -> Participant.compareByAge(p1, p2));
    

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35. Example
    

    Collections.sort(participants,

    Participant::compareByAge);
    

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36. From
    

    Collections.sort(participants,
    new Comparator() {

    @Override

    public int compare(Participant p1, Participant p2) {

    return Participant.compareByAge(p1,p2);

    }

    });
    

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37. To
    

    Collections.sort(participants,

    Participant::compareByAge);
    

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38. Android N
    

    Collections.sort(participants,

    Comparator.comparingInt(Participant::getAge));
    

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39. Syntax
    

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40. Syntax
    • Reference to a static method
    (s) -> String.valueOf(s)
    

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41. Syntax
    • Reference to a static method
    (s) -> String.valueOf(s)
    String::valueOf
    

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42. Syntax
    • Reference to an instance method of a particular
    object
    (o) -> o.toString()
    

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43. Syntax
    • Reference to an instance method of a particular
    object
    (o) -> o.toString()
    o::toString
    

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44. Syntax
    • Reference to an instance method of an arbitrary
    object of a particular type
    Arrays.sort((a,b) -> a.compareToIgnoreCase(b))
    

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45. Syntax
    • Reference to an instance method of an arbitrary
    object of a particular type
    Arrays.sort((a,b) -> a.compareToIgnoreCase(b))
    Arrays.sort(String::compareToIgnoreCase)
    

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46. Syntax
    • Reference to an instance method of an arbitrary
    object of a particular type
    Arrays.sort((a,b) -> a.compareToIgnoreCase(b))
    Arrays.sort(String::compareToIgnoreCase)
    

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47. Syntax
    • Reference to a constructor
    () -> new String()
    

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48. Syntax
    • Reference to a constructor
    () -> new String()
    String::new
    

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49. Method count
    

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50. Method count
    • Exploring Java’s Hidden Costs (Jake Wharton)
    • 23:30 — Lambdas
    

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51. Method count
    From: https://speakerdeck.com/jakewharton/exploring-hidden-java-costs-360-andev-july-2016?slide=126
    

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52. Comparison with Kotlin
    • Claims no increase in method count, bytecode
    inserted directly (see post)
    

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53. Backward-compatible
    features
    • Lambdas
    • Method references
    • Type annotations
    

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54. Type annotations
    Annotations can now be used anywhere you use a type
    

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55. Annotations before Java 8
    • Method: @Override void onCreate()…
    • Class: 

    @RunWith(JUnit4Runner.class) 

    public class TestDoggieTreats {…
    • Parameters, return values

    @NonNull String prepareText(@Nullable input);
    

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56. Type annotations
    • Anywhere you use a type
    • Class instantiation: new @Interned MyObject();
    • Type cast: myString = (@NonNull String) str;
    • Implements clause: class UnmodifiableList
    implements @Readonly List<@Readonly T> { ... }
    • Throws: void monitorTemperature() throws @Critical
    TemperatureException { ... }
    

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57. Type annotations
    • Anywhere you use a type
    • Class instantiation: new @Interned MyObject();
    • Type cast: myString = (@NonNull String) str;
    • Implements clause: class UnmodifiableList
    implements @Readonly List<@Readonly T> { ... }
    • Throws: void monitorTemperature() throws @Critical
    TemperatureException { ... }
    

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58. Requirements
    • Using the Jack compiler
    • Setting language compatibility to 1.8
    • (more on that later)
    

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59. Nougat only
    

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60. Nougat only features
    • Streams
    • Default and static interface methods
    • Repeatable annotations
    

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61. Streams
    A new abstraction that lets you process data in a
    declarative way
    

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62. Streams
    Data manipulation like you always dreamed of.
    Can filter, map & reduce while being traversed, sequentially or in parallel.
    

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63. Example
    public interface FilterCondition {

    boolean accept(T candidate);

    }

    List filter(List 

    participants, 

    FilterCondition 

    filterCondition)
    

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64. Example
    List output = new ArrayList<>();

    

    for (Participant participant : participants) {

    if (filterCondition.accept(participant)) {

    output.add(participant);

    }

    }

    

    return output;

    

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65. Example
    return participants.stream()

    .filter(filterCondition::accept)

    .collect(Collectors.toList());
    

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66. Example
    return participants.stream()

    .filter(filterCondition::accept)

    .collect(Collectors.toList());
    

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67. Example
    return participants.stream()

    .filter((participant) -> 

    filterCondition.accept(participant))

    .collect(Collectors.toList());
    

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68. Example
    return participants.stream()

    .filter(filterCondition::accept)

    .collect(Collectors.toList());
    

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69. Example
    return participants.stream()

    .filter(filterCondition::accept)

    .collect(Collectors.toList());
    

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70. Example
    List filter(

    List participants,
    Predicate predicate)

    

    return participants.stream()

    .filter(predicate)

    .collect(Collectors.toList());
    

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71. Example
    List filter(

    List participants,
    Predicate predicate)

    

    return participants.stream()

    .filter(predicate)

    .collect(Collectors.toList());
    

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72. Find the youngest
    participants

    .stream()

    .min(Comparator.comparingInt(

    Participant::getAge))

    .ifPresent(

    participant -> 

    Timber.d("Youngest participant %s", 

    participant.getName()));

    

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73. Find the youngest
    participants

    .stream()

    .min(Comparator.comparingInt(

    Participant::getAge))

    .ifPresent(

    participant -> 

    Timber.d("Youngest participant %s", 

    participant.getName()));

    

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74. Find the youngest
    participants

    .stream()

    .min(Comparator.comparingInt(

    Participant::getAge))

    .ifPresent(

    participant -> 

    Timber.d("Youngest participant %s", 

    participant.getName()));

    

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75. Find the youngest
    participants

    .stream()

    .min(Comparator.comparingInt(

    Participant::getAge))

    .ifPresent(

    participant -> 

    Timber.d("Youngest participant %s", 

    participant.getName()));

    

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76. Find the youngest
    participants

    .parallelStream()

    .min(Comparator.comparingInt(

    Participant::getAge))

    .ifPresent(

    participant -> 

    Timber.d("Youngest participant %s", 

    participant.getName()));

    

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77. Map
    Set names =

    participants.stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toSet());
    

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78. Map
    Set names =

    participants.stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toSet());
    

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79. Map
    Set names =

    participants.stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toSet());
    

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80. Map
    SortedSet names =

    participants.stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toCollection(TreeSet::new));
    

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81. Map
    SortedSet names =

    participants.stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toCollection(TreeSet::new));
    

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82. Streams are lazy
    • The intermediate operations are always lazy
    • The “terminal” operations produce values or side-
    effects
    

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83. Map
    SortedSet names =

    participants

    .stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toCollection(TreeSet::new));
    

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84. Map
    SortedSet names =

    participants

    .stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toCollection(TreeSet::new));
    

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85. Map
    SortedSet names =

    participants

    .stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toCollection(TreeSet::new));
    

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86. Map
    SortedSet names =

    participants

    .stream()

    .map(Participant::getName)

    .sorted()

    .collect(Collectors.toCollection(TreeSet::new));
    

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87. Map
    SortedSet names =

    participants

    .stream()

    .map(Participant::getName)

    .sorted()

    .limit(2)

    .collect(Collectors.toCollection(TreeSet::new));
    

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88. Nougat only features
    • Streams
    • Default and static interface methods
    • Repeatable annotations
    

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89. Default methods
    

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90. Default methods
    How do streams work?
    

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91. Default methods
    • How to build “streams” without breaking all custom
    collections?
    • Collection interface adds:
    • boolean removeIf(Predicate super E> filter)
    • Spliterator spliterator()
    • Stream stream()
    • Stream parallelStream()
    

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92. Default methods
    • default boolean removeIf(Predicate super E> filter)
    • default Spliterator spliterator()
    • default Stream stream()
    • default Stream parallelStream()
    

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93. Default methods
    Enables you to add new (default) implementations to
    interfaces so implementing classes don’t need to change
    

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94. Collection
    @Override

    default Spliterator spliterator() {

    return Spliterators.spliterator(this, 0);

    }

    default Stream stream() {

    return StreamSupport.stream(spliterator(), false);

    }
    

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95. Implementing classes
    • When you implement an interface that contains a
    default method, you can do the following:
    • Not mention the default method at all, which lets
    your implementation use the default method
    • Override the default method
    • Reuse the default method implementation using
    super
    

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96. Implementing classes
    • Not mention the default method at all, which lets
    your implementation use the default method
    

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97. Implementing classes
    • Not mention the default method at all, which lets
    your implementation use the default method
    class FancyList implements Collection
    

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98. Implementing classes
    • Override the default method
    

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99. Implementing classes
    • Override the default method
    class FancyList implements Collection
    @Override

    public Stream stream() {

    return ….. 

    }
    

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100. Implementing classes
     • Reuse the default method implementation using
     super
     

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101. Implementing classes
     • Reuse the default method implementation using super
     class FancyList implements Collection
     @Override

     Stream stream() {

     // ……

     return super.stream();

     }
     

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102. Extending interface
     • When you extend an interface that contains a
     default method, you can do the following:
     • Not mention the default method at all, which lets
     your extended interface inherit the default
     method
     • Redeclare the default method, which makes it
     abstract
     • Redefine the default method, which overrides it
     

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103. Extending interface
     • Not mention the default method at all, which lets
     your extended interface inherit the default method
     

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104. Extending interface
     • Not mention the default method at all, which lets
     your extended interface inherit the default method
     interface Set extends Collection {

     ….

     }
     

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105. Extending interface
     • Redeclare the default method, which makes it
     abstract
     

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106. Extending interface
     • Redeclare the default method, which makes it
     abstract

     

     interface FancySet extends Collection {

     ….

     Stream stream();

     }
     

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107. Extending interface
     • Redefine the default method, which overrides it
     

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108. Extending interface
     • Redefine the default method, which overrides it
     interface Set extends Collection {

     ….

     @Override default Spliterator spliterator() {

     return Spliterators.spliterator(this,
     Spliterator.DISTINCT);

     }

     }
     

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109. Multiple inheritance?
     public interface A {

     default void foo() {

     Timber.d(“Calling A.foo()");

     }

     }

     

     

     

     

     

     

     public class ProblematicClass
     implements A, B {

     //…..

     }
     public interface B {

     default void foo() {

     Timber.d(“Calling B.foo()");

     }

     }
     

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110. Multiple inheritance?
     public interface A {

     default void foo() {

     Timber.d(“Calling A.foo()");

     }

     }

     

     

     

     

     

     

     public class ProblematicClass
     implements A, B {

     //…..

     }
     public interface B {

     default void foo() {

     Timber.d(“Calling B.foo()");

     }

     }
     

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111. Multiple inheritance
     public class ProblematicClass implements A, B {
     }
     // error: class ProblematicClass inherits unrelated
     defaults for foo() from types A and B
     

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112. Multiple inheritance
     public class ProblematicClass implements A, B {
     }
     // error: class ProblematicClass inherits unrelated
     defaults for foo() from types A and B
     

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113. Multiple inheritance
     public class ProblematicClass implements A, B {
     @Override public void foo() {
     }
     }
     

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114. Multiple inheritance
     public class ProblematicClass implements A, B {
     @Override public void foo() {
     A.super.foo();
     B.super.foo();
     }
     }
     

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115. Instances methods vs
     default methods
     public class Horse {
     public String identifyMyself() {
     return "I am a horse.";
     }
     }
     public interface Flyer {
     default public String identifyMyself() {
     return "I am able to fly.";
     }
     }
     public interface Mythical {
     default public String identifyMyself() {
     return "I am a mythical creature.";
     }
     }
     public class Pegasus extends Horse implements
     Flyer, Mythical {
     public static void main(String... args) {
     Pegasus myApp = new Pegasus();
     System.out.println(myApp.identifyMyself());
     }
     }
     

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116. Instances methods vs
     default methods
     public class Horse {
     public String identifyMyself() {
     return "I am a horse.";
     }
     }
     public interface Flyer {
     default public String identifyMyself() {
     return "I am able to fly.";
     }
     }
     public interface Mythical {
     default public String identifyMyself() {
     return "I am a mythical creature.";
     }
     }
     public class Pegasus extends Horse implements
     Flyer, Mythical {
     public static void main(String... args) {
     Pegasus myApp = new Pegasus();
     System.out.println(myApp.identifyMyself());
     }
     }
     

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117. Instances methods vs
     default methods
     public class Horse {
     public String identifyMyself() {
     return "I am a horse.";
     }
     }
     public interface Flyer {
     default public String identifyMyself() {
     return "I am able to fly.";
     }
     }
     public interface Mythical {
     default public String identifyMyself() {
     return "I am a mythical creature.";
     }
     }
     public class Pegasus extends Horse implements
     Flyer, Mythical {
     public static void main(String... args) {
     Pegasus myApp = new Pegasus();
     System.out.println(myApp.identifyMyself());
     }
     }
     

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118. Instances methods vs
     default methods
     public class Horse {
     public String identifyMyself() {
     return "I am a horse.";
     }
     }
     public interface Flyer {
     default public String identifyMyself() {
     return "I am able to fly.";
     }
     }
     public interface Mythical {
     default public String identifyMyself() {
     return "I am a mythical creature.";
     }
     }
     public class Pegasus extends Horse implements
     Flyer, Mythical {
     public static void main(String... args) {
     Pegasus myApp = new Pegasus();
     System.out.println(myApp.identifyMyself());
     }
     }
     

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119. Instances methods vs
     default methods
     public class Horse {
     public String identifyMyself() {
     return "I am a horse.";
     }
     }
     public interface Flyer {
     default public String identifyMyself() {
     return "I am able to fly.";
     }
     }
     public interface Mythical {
     default public String identifyMyself() {
     return "I am a mythical creature.";
     }
     }
     public class Pegasus extends Horse implements
     Flyer, Mythical {
     public static void main(String... args) {
     Pegasus myApp = new Pegasus();
     System.out.println(myApp.identifyMyself());
     }
     }
     

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120. Instances methods vs
     default methods
     • Instance methods are preferred over interface
     default methods
     • The method Pegasus.identifyMyself returns the
     string I am a horse.
     

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121. Static methods
     • Comparator gains:

     

     public static >
     Comparator reverseOrder() {

     return Collections.reverseOrder();

     }
     

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122. Nougat only features
     • Streams
     • Default and static interface methods
     • Repeatable annotations
     

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123. Repeatable
     annotations
     You may now create annotations that can be repeated
     

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124. Example
     @Schedule(dayOfMonth="last")

     @Schedule(dayOfWeek="Fri", hour="23")

     public void doPeriodicCleanup() { ... }
     

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125. How-to
     • Declare the annotation as repeatable
     • Declare a containing annotation type
     • See: https://docs.oracle.com/javase/tutorial/java/
     annotations/repeating.html
     

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126. Pre-N alternatives
     

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127. Alternative options
     • Lambdas -> Retrolambda
     • Streams -> Lightweight Stream API
     

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128. Build setup
     

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129. Requirements
     • This applies for all Java 8 features
     • Requirements:
     • Use Jack & Jill
     • Set language compatibility
     • Android Studio 2.1+
     • Build tools 21.1.1+
     

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130. A bit about Jack
     • Jack is a new Android toolchain
     • Compiles Java source into Android dex bytecode
     • Replaces the previous toolchain
     • javac, ProGuard, jarjar, dx etc.
     

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131. A bit about Jack
     

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132. What’s Jill?
     • Jill translates the existing .jar libraries into the new
     library format
     

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133. A bit about Jill
     

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134. How to setup
     • Instructions at : https://developer.android.com/
     guide/platform/j8-jack.html
     

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135. Annotation processor
     • If you’re using Dagger, Butterknife etc.
     apply plugin: 'com.neenbedankt.android-apt'

     apt 'com.google.dagger:dagger-compiler:2.2'
     

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136. Annotation processor
     annotationProcessor
     ‘com.google.dagger:dagger-compiler:2.2’
     

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137. Annotation processor
     • Guide: https://bitbucket.org/hvisser/android-apt/
     wiki/Migration
     

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138. Known issues
     • Jack does not generate intermediate class files
     when compiling an app, so it breaks some tools
     • Instant run doesn’t work with Jack
     • Lint that operates on class files
     • JaCoCo instrumentation (now fixed)
     • Possible Kotlin issues
     

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139. Known issues
     • Updated list: https://source.android.com/source/
     known-issues.html
     • The one under Java 8 features doesn’t seem to be
     updated
     • File bugs: http://tools.android.com/filing-bugs
     

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140. Resources
     

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141. Links — Lambdas
     • Many lambda examples: docs.oracle.com/javase/
     tutorial/java/javaOO/lambdaexpressions.html
     • Lambda tutorial: https://github.com/
     AdoptOpenJDK/lambda-tutorial
     • Official docs on Streams: http://docs.oracle.com/
     javase/tutorial/collections/streams/
     • Streams tutorial: http://blog.hartveld.com/2013/03/
     jdk-8-33-stream-api.html
     

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142. Other talks
     • Exploring Java’s Hidden Costs (@JakeWharton)
     • Jack and Jill build system (Eric Lafortune)
     • API Design With Java 8 Lambda and Streams
     (@stuartmarks & @BrianGoetz)
     

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143. Thank you
     http://bit.do/droidcon-java8

     https://github.com/anothem/
     java8-android
     

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