EqualsVerifier, ErrorProne и все-все-все (Гейзенбаг Питер 2018)

Transcript

1. EqualsVerifier, ErrorProne 

   и все, все, все …
   Андрей Сатарин
   
   @asatarin
   

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2. О чем я сегодня расскажу
   • EqualsVerifier
   • Зачем он нужен
   • Как он может вам помочь
   • ErrorProne
   • Что это
   • Какие проблемы решает
   2
   

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3. Зачем все это нужно?
   • Есть куча низкоуровневых ошибок, которые сложно найти
   • Эти ошибки могут очень сильно влиять на видимое поведение
   • Так же эти ошибки приводят к общему “гниению” кода
   3
   

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4. @Test
   public void setSizeIsTwo() {
   final Set set = new HashSet!<>();
   final Value a = new Value(0, 0);
   final ChildValue b = new ChildValue(0, 0, -29791);
   set.add(a);
   set.add(b);
   assertEquals(2, set.size());
   }
   4
   

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5. @Test
   public void setSizeIsTwo() {
   final Set set = new HashSet!<>();
   final Value a = new Value(0, 0);
   final ChildValue b = new ChildValue(0, 0, -29791);
   set.add(a);
   set.add(b);
   assertEquals(2, set.size());
   }
   5
   

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6. @Test
   public void setSizeIsTwo() {
   final Set set = new HashSet!<>();
   final Value a = new Value(0, 0);
   final ChildValue b = new ChildValue(0, 0, -29791);
   set.add(b);
   set.add(a);
   assertEquals(2, set.size());
   }
   6
   

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7. Часть I
   EqualsVerifier
   7
   

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8. Object!::equals
   public boolean equals(Object obj) {
   return (this !== obj);
   }
   8
   

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9. final Object a = new Object();
   final Object b = new Object();
   assertTrue(a !== a);
   assertTrue(a.equals(a));
   assertFalse(a !== b);
   assertFalse(a.equals(b));
   9
   

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10. Integer!::equals
    public boolean equals(Object obj) {
    if (obj instanceof Integer) {
    return value !== ((Integer)obj).intValue();
    }
    return false;
    }
    10
    

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11. final Integer x = new Integer(43534);
    final Integer y = new Integer(43534);
    assertTrue(x !== x);
    assertTrue(x.equals(x));
    assertFalse(x !== y);
    assertTrue(x.equals(y));
    11
    

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12. final Integer x = new Integer(43534);
    final Integer y = new Integer(43534);
    assertTrue(x !== x);
    assertTrue(x.equals(x));
    assertFalse(x !== y);
    assertTrue(x.equals(y));
    12
    

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13. • Иногда в нашем коде приходится реализовывать equals()
    • Где есть реализация, там нужны и тесты
    13
    

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14. Кто помнит три свойства, которым
    должна удовлетворять корректная
    реализация equals()?
    14
    

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15. I know Java 

    equals contract
    15
    

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16. Три Четыре свойства
    • Рефлексия (reflexive)
    • Симметрия (symmetric)
    • Транзитивность (transitive)
    • Консистентность (consistent)
    16
    

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17. Рефлексия
    Для любого a, всегда верно a.equals(a)
    a !== a
    17
    

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18. Симметрия
    Если верно a.equals(b)

    !=> тогда верно b.equals(a)
    a !== b !=> b !== a
    18
    

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19. Транзитивность
    Если верно a.equals(b) и b.equals(c) 

    !=> тогда верно a.equals(с)
    !=>
    a !== b
    b !== c
    a !== c
    19
    

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20. Консистентность
    Если a.equals(b) сейчас 

    !=> тогда a.equals(b) в будущем
    a !== b !=> a !== b
    20
    

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21. Josh Bloch, Effective Java
    “A common source of bugs is the failure to override the
    hashCode method. You must override hashCode in every class
    that overrides equals. ”
    21
    

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22. Поэтому дальше я говорю про оба метода
    • Object::equals
    • Object::hashCode
    equals() + hashCode()
    22
    

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23. Пример класса
    public class ParsedURL {
    private final Protocol protocol;
    private final String hostname;
    private final int port;
    private final String path;
    private final Map parameters;
    …
    }
    23
    

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24. Как все это тестировать?
    24
    

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25. Вариант 1
    Никак не тестировать:
    • Просто и быстро
    • Не надежно
    25
    

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26. Вариант 2
    Очень простые тесты:
    • Относительно просто и быстро
    • Все еще не надежно
    26
    

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27. Примеры “простых” тестов
    • 1 на равенство двух не идентичных объектов
    • 5 на неравенство двух разных объектов
    • 1 на рефлексию объекта с самим собой
    • 1 на симметрию двух равных объектов
    • 1 на консистентность (как это проверить вообще)?
    27
    

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28. @Test
    public void testSimple() {
    final ParsedURL u1 = new ParsedURL(:));
    final ParsedURL u2 = new ParsedURL(:D);
    assertNotEquals(u1, u2);
    }
    “Простой” тест
    28
    

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29. • Получилось примерно 10 тестов
    • Достаточно ли этого?
    29
    

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30. Таких тестов недостаточно
    • Что с классами-потомками и классами-предками?
    • Что с double/float полями?
    • Что с nullable полями?
    • Что будет при изменении класса?
    30
    

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31. Таких тестов недостаточно
    • Что с классами-потомками и классами-предками?
    • Что с double/float полями?
    • Что с nullable полями?
    • Что будет при изменении класса?
    • Мы забыли про Object::hashCode
    31
    

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32. Вариант 3
    Тесты с EqualsVerifier:
    • Просто и быстро
    • Очень надежно
    32
    

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33. Пример теста с EqualsVerifier
    @Test
    public void testEqualsContract() {
    EqualsVerifier
    .forClass(Value.class)
    .verify();
    }
    33
    

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34. • Один (!) тест с EqualsVerifier дает 100% покрытие по строкам кода
    • Если это не так — EqualsVerifier выдаст ошибку
    34
    

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35. Пример 1

    Хороший equals при плохом классе
    35
    

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36. public final class Value {
    private int x;
    private int y;
    public Value(int x, int y) {
    this.x = x;
    this.y = y;
    }
    …
    @Override
    public boolean equals(Object o) {
    if (this !== o) return true;
    if (!(o instanceof Value)) return false;
    Value value = (Value) o;
    return x !== value.x !&& y !== value.y;
    }
    }
    36
    

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37. java.lang.AssertionError:
    Mutability: equals depends on mutable field x.
    37
    

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38. Чем это опасно?
    @Test
    public void testValueStaysInSet() {
    final Set set = new HashSet!<>();
    final Value a = new Value(123, 789);
    set.add(a);
    assertTrue(set.contains(a));
    a.setX(0);
    assertFalse(set.contains(a));
    }
    38
    

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39. Как починить?
    1. Починить код
    2. Рассказать тестам, что так и надо
    39
    

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40. public final class Value {
    private final int x;
    private final int y;
    public Value(int x, int y) {
    this.x = x;
    this.y = y;
    }
    …
    @Override
    public boolean equals(Object o) {
    if (this !== o) return true;
    if (!(o instanceof Value)) return false;
    Value value = (Value) o;
    return x !== value.x !&& y !== value.y;
    }
    }
    40
    

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41. 2. Рассказать тестам, что так и надо
    @Test
    public void testLooseEqualsContract() {
    EqualsVerifier
    .forClass(Value.class)
    .suppress(Warning.NONFINAL_FIELDS)
    .verify();
    }
    41
    

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42. Пример 2

    Сын за отца в ответе
    42
    

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43. public class ChildValue extends Value {
    private int z;
    public ChildValue(int x, int y, int z) {
    super(x, y);
    this.z = z;
    }
    @Override
    public boolean equals(Object o) {
    if (this !== o) return true;
    if (!(o instanceof ChildValue))
    return false;
    if (!super.equals(o)) return false;
    ChildValue that = (ChildValue) o;
    return z !== that.z;
    }
    43
    

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44. java.lang.AssertionError: Symmetry:

    ChildValue{z=1, x=1, y=1} 

    does not equal superclass instance

    Value{x=1, y=1}
    44
    

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45. java.lang.AssertionError: Symmetry:

    ChildValue{z=1, x=1, y=1} 

    does not equal superclass instance

    Value{x=1, y=1}
    45
    

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46. Тест, который провел EqualsVerifier
    final Value a = new Value(1, 1);
    final ChildValue b = new ChildValue(1, 1, 1);
    assertTrue("a, b", a.equals(b));
    assertFalse("b, a", b.equals(a));
    46
    

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47. Чем это опасно?
    @Test
    public void setSizeIsTwo() {
    final Set set = new HashSet!<>();
    final Value a = new Value(0, 0);
    final ChildValue b = new ChildValue(0, 0, -29791);
    set.add(a);
    set.add(b);
    assertEquals(2, set.size());
    }
    47
    

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48. @Test
    public void setSizeIsTwo() {
    final Set set = new HashSet!<>();
    final Value a = new Value(0, 0);
    final ChildValue b = new ChildValue(0, 0, -29791);
    set.add(b);
    set.add(a);
    assertEquals(1, set.size());
    }
    Чем это опасно?
    48
    

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49. Как чинить асимметрию?
    public boolean canEqual(Object other) {
    …
    }
    

    https://www.artima.com/lejava/articles/equality.html
    49
    

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50. Типичная ошибка — реализуем
    equals() специально для тестов
    50
    

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51. • Очень хотим вот так писать

    assertEquals(expected, actual);
    • Это плохой equals():
    • Не несет смысл, важный для доменной области
    • Будет незаметно использован в ПРОД коде
    51
    Реализуем equals() для тестов
    

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52. Вот так хорошо
    assertTrue(
    EqualsBuilder.reflectionEquals(
    expected, actual
    )
    );
    52
    

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53. А вот так лучше
    assertThat(
    actual,

    Matchers.reflectionEquals(expected)
    );
    53
    

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54. Типичные возражения
    54
    

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55. Типичные возражения
    • Я использую EqualsBuilder и HashCodeBuilder
    • Я использую кодогенерацию из IDEA
    55
    

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56. Часть проблем остается
    • Проблемы с мутабельными полями остаются
    • Проблемы с наследниками остаются
    • Возможные ошибки при добавлении полей остаются
    • Возможно ошибок нет сейчас, но они могут появится в будущем
    56
    

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57. Альтернативные решения
    • Google Auto Value
    • @EqualsAndHashCode из Lombok
    • Дождаться появления value классов в Java
    57
    

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58. EqualsVerifier выводы
    • 100% покрытие одной строчкой кода
    • Не надо писать новые тесты при изменении класса
    • (Почти) Не надо помнить детали контракта equals()
    • Все это гарантируется не только сегодня, но и в будущем
    • Бесплатно как “бесплатное пиво”
    58
    

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59. Отлично, есть относительно простой способ искать ошибки в очень
    небольшой части кода. 

    

    А хочется очень простой способ искать ошибки по всему коду.
    59
    

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60. Часть II
    ErrorProne
    60
    

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61. Статические анализаторы
    • FindBugs
    • SonarQube
    • PMD
    61
    

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62. ErrorProne — компилятор на
    стероидах
    62
    

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63. Как работает ErrorProne
    Исходный

    код
    Байт код 

    в jar’ах
    Компилятор 

    (javac)
    Класс файлы
    63
    

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64. Как работает ErrorProne
    Исходный

    код
    Байт код 

    в jar’ах
    Компилятор 

    (javac)
    Класс файлы
    Компилятор 

    (javac + ErrorProne)
    Класс файлы

    (еще раз)
    64
    

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65. Интеграция
    • IntelliJ IDEA
    • Ant
    • Maven
    • Gradle
    • Bazel
    65
    

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66. http://errorprone.info/
    “Using Error Prone to augment the compiler’s type analysis, you
    can catch more mistakes before they cost you time, or end up
    as bugs in production. 

    We use Error Prone in Google’s Java build system 

    to eliminate classes of serious bugs from entering our code,
    and we’ve open-sourced it, so you can too!”
    66
    

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67. http://errorprone.info/
    “Using Error Prone to augment the compiler’s type analysis, you
    can catch more mistakes before they cost you time, or end up
    as bugs in production. 

    We use Error Prone in Google’s Java build system 

    to eliminate classes of serious bugs from entering our code,
    and we’ve open-sourced it, so you can too!”
    67
    

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68. Doug Lea
    “Definitely embarrassing. I guess I’m back to liking Error Prone
    even though it sometimes annoys me :-)”
    68
    

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69. Уровень 1

    Подключил, починил и забыл
    69
    

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70. AndroidInjectionBeforeSuper

    AndroidInjection.inject() should always be invoked before calling super.lifecycleMethod()
    
    ArrayEquals

    Reference equality used to compare arrays
    
    ArrayFillIncompatibleType

    Arrays.fill(Object[], Object) called with incompatible types.
    
    ArrayHashCode

    hashcode method on array does not hash array contents
    
    ArrayToString

    Calling toString on an array does not provide useful information
    
    ArraysAsListPrimitiveArray

    Arrays.asList does not autobox primitive arrays, as one might expect.
    
    AsyncCallableReturnsNull

    AsyncCallable should not return a null Future, only a Future whose result is null.
    
    AsyncFunctionReturnsNull

    AsyncFunction should not return a null Future, only a Future whose result is null.
    
    AutoValueConstructorOrderChecker

    Arguments to AutoValue constructor are in the wrong order
    
    BadShiftAmount

    Shift by an amount that is out of range
    
    BundleDeserializationCast

    Object serialized in Bundle may have been flattened to base type.
    
    ChainingConstructorIgnoresParameter

    The called constructor accepts a parameter with the same name and type as one of its caller's parameters, but its caller doesn't pass that parameter to it. It's likely that it was intended to.
    
    CheckReturnValue

    Ignored return value of method that is annotated with @CheckReturnValue
    
    CollectionIncompatibleType

    Incompatible type as argument to Object-accepting Java collections method
    
    ComparableType

    Implementing 'Comparable' where T is not compatible with the implementing class.
    
    ComparisonOutOfRange

    Comparison to value that is out of range for the compared type
    
    CompatibleWithAnnotationMisuse

    @CompatibleWith's value is not a type argument.
    
    CompileTimeConstant

    Non-compile-time constant expression passed to parameter with @CompileTimeConstant type annotation.
    
    ComplexBooleanConstant

    Non-trivial compile time constant boolean expressions shouldn't be used.
    
    ConditionalExpressionNumericPromotion

    A conditional expression with numeric operands of differing types will perform binary numeric promotion of the operands; when these operands are of reference types, the expression's result may not be of the expected type.
    
    ConstantOverflow

    Compile-time constant expression overflows
    
    DaggerProvidesNull

    Dagger @Provides methods may not return null unless annotated with @Nullable
    
    DeadException

    Exception created but not thrown
    
    DeadThread

    Thread created but not started
    
    DoNotCall

    This method should not be called.
    
    EqualsNaN

    == NaN always returns false; use the isNaN methods instead
    
    EqualsReference

    == must be used in equals method to check equality to itself or an infinite loop will occur.
    
    ForOverride

    Method annotated @ForOverride must be protected or package-private and only invoked from declaring class, or from an override of the method
    
    FormatString

    Invalid printf-style format string
    
    FormatStringAnnotation

    Invalid format string passed to formatting method.
    
    FunctionalInterfaceMethodChanged

    Casting a lambda to this @FunctionalInterface can cause a behavior change from casting to a functional superinterface, which is surprising to users. Prefer decorator methods to this surprising behavior.
    
    FuturesGetCheckedIllegalExceptionType

    Futures.getChecked requires a checked exception type with a standard constructor.
    
    GetClassOnAnnotation

    Calling getClass() on an annotation may return a proxy class
    
    GetClassOnClass

    Calling getClass() on an object of type Class returns the Class object for java.lang.Class; you probably meant to operate on the object directly
    
    GuardedBy

    Checks for unguarded accesses to fields and methods with @GuardedBy annotations
    
    GuiceAssistedInjectScoping

    Scope annotation on implementation class of AssistedInject factory is not allowed
    
    GuiceAssistedParameters

    A constructor cannot have two @Assisted parameters of the same type unless they are disambiguated with named @Assisted annotations.
    
    GuiceInjectOnFinalField

    Although Guice allows injecting final fields, doing so is disallowed because the injected value may not be visible to other threads.
    
    HashtableContains

    contains() is a legacy method that is equivalent to containsValue()
    
    IdentityBinaryExpression

    A binary expression where both operands are the same is usually incorrect.
    
    Immutable

    Type declaration annotated with @Immutable is not immutable
    
    ImmutableModification

    Modifying an immutable collection is guaranteed to throw an exception and leave the collection unmodified
    
    IncompatibleArgumentType

    Passing argument to a generic method with an incompatible type.
    
    IndexOfChar

    The first argument to indexOf is a Unicode code point, and the second is the index to start the search from
    
    InexactVarargsConditional

    Conditional expression in varargs call contains array and non-array arguments
    
    InfiniteRecursion

    This method always recurses, and will cause a StackOverflowError
    
    InjectMoreThanOneScopeAnnotationOnClass

    A class can be annotated with at most one scope annotation.
    
    InvalidPatternSyntax

    Invalid syntax used for a regular expression
    
    InvalidTimeZoneID

    Invalid time zone identifier. TimeZone.getTimeZone(String) will silently return GMT instead of the time zone you intended.
    
    IsInstanceOfClass

    The argument to Class#isInstance(Object) should not be a Class
    
    IsLoggableTagLength

    Log tag too long, cannot exceed 23 characters.
    
    JUnit3TestNotRun

    Test method will not be run; please correct method signature (Should be public, non-static, and method name should begin with "test").
    
    JUnit4ClassAnnotationNonStatic

    This method should be static
    
    JUnit4SetUpNotRun

    setUp() method will not be run; please add JUnit's @Before annotation
    
    JUnit4TearDownNotRun

    tearDown() method will not be run; please add JUnit's @After annotation
    
    JUnit4TestNotRun

    This looks like a test method but is not run; please add @Test and @Ignore, or, if this is a helper method, reduce its visibility.
    
    JUnitAssertSameCheck

    An object is tested for reference equality to itself using JUnit library.
    
    JavaxInjectOnAbstractMethod

    Abstract and default methods are not injectable with javax.inject.Inject
    
    LiteByteStringUtf8

    This pattern will silently corrupt certain byte sequences from the serialized protocol message. Use ByteString or byte[] directly
    
    LoopConditionChecker

    Loop condition is never modified in loop body.
    
    MislabeledAndroidString

    Certain resources in android.R.string have names that do not match their content
    
    MissingSuperCall

    Overriding method is missing a call to overridden super method
    
    MisusedWeekYear

    Use of "YYYY" (week year) in a date pattern without "ww" (week in year). You probably meant to use "yyyy" (year) instead.
    
    MockitoCast

    A bug in Mockito will cause this test to fail at runtime with a ClassCastException
    
    MockitoUsage

    Missing method call for verify(mock) here
    
    ModifyingCollectionWithItself

    Using a collection function with itself as the argument.
    
    MoreThanOneInjectableConstructor

    This class has more than one @Inject-annotated constructor. Please remove the @Inject annotation from all but one of them.
    
    MustBeClosedChecker

    The result of this method must be closed.
    
    NCopiesOfChar

    The first argument to nCopies is the number of copies, and the second is the item to copy
    
    NonCanonicalStaticImport

    Static import of type uses non-canonical name
    
    NonFinalCompileTimeConstant

    @CompileTimeConstant parameters should be final or effectively final
    
    NonRuntimeAnnotation

    Calling getAnnotation on an annotation that is not retained at runtime.
    
    NullTernary

    This conditional expression may evaluate to null, which will result in an NPE when the result is unboxed.
    
    OptionalEquality

    Comparison using reference equality instead of value equality
    
    OverlappingQualifierAndScopeAnnotation

    Annotations cannot be both Scope annotations and Qualifier annotations: this causes confusion when trying to use them.
    
    OverridesJavaxInjectableMethod

    This method is not annotated with @Inject, but it overrides a method that is annotated with @javax.inject.Inject. The method will not be Injected.
    
    PackageInfo

    Declaring types inside package-info.java files is very bad form
    
    PreconditionsCheckNotNull

    Literal passed as first argument to Preconditions.checkNotNull() can never be null
    
    PreconditionsCheckNotNullPrimitive

    First argument to Preconditions.checkNotNull() is a primitive rather than an object reference
    
    PredicateIncompatibleType

    Using ::equals as an incompatible Predicate; the predicate will always return false
    
    PrivateSecurityContractProtoAccess

    Access to a private protocol buffer field is forbidden. This protocol buffer carries a security contract, and can only be created using an approved library. Direct access to the fields is forbidden.
    
    ProtoFieldNullComparison

    Protobuf fields cannot be null
    
    ProtocolBufferOrdinal

    To get the tag number of a protocol buffer enum, use getNumber() instead.
    
    ProvidesMethodOutsideOfModule

    @Provides methods need to be declared in a Module to have any effect.
    
    RandomCast

    Casting a random number in the range [0.0, 1.0) to an integer or long always results in 0.
    
    RandomModInteger

    Use Random.nextInt(int). Random.nextInt() % n can have negative results
    
    RectIntersectReturnValueIgnored

    Return value of android.graphics.Rect.intersect() must be checked
    
    RestrictedApiChecker

    Check for non-whitelisted callers to RestrictedApiChecker.
    
    ReturnValueIgnored

    Return value of this method must be used
    
    SelfAssignment

    Variable assigned to itself
    
    SelfComparison

    An object is compared to itself
    
    SelfEquals

    Testing an object for equality with itself will always be true.
    
    ShouldHaveEvenArgs

    This method must be called with an even number of arguments.
    
    SizeGreaterThanOrEqualsZero

    Comparison of a size >= 0 is always true, did you intend to check for non-emptiness?
    
    StreamToString

    Calling toString on a Stream does not provide useful information
    
    StringBuilderInitWithChar

    StringBuilder does not have a char constructor; this invokes the int constructor.
    
    SuppressWarningsDeprecated

    Suppressing "deprecated" is probably a typo for "deprecation"
    
    ThrowIfUncheckedKnownChecked

    throwIfUnchecked(knownCheckedException) is a no-op.
    
    ThrowNull

    Throwing 'null' always results in a NullPointerException being thrown.
    
    TruthSelfEquals

    isEqualTo should not be used to test an object for equality with itself; the assertion will never fail.
    
    TryFailThrowable

    Catching Throwable/Error masks failures from fail() or assert*() in the try block
    
    TypeParameterQualifier

    Type parameter used as type qualifier
    
    UnnecessaryTypeArgument

    Non-generic methods should not be invoked with type arguments
    
    UnusedAnonymousClass

    Instance created but never used
    
    UnusedCollectionModifiedInPlace

    Collection is modified in place, but the result is not used
    
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71. AndroidInjectionBeforeSuper

    AndroidInjection.inject() should always be invoked before calling super.lifecycleMethod()
    
    ArrayEquals

    Reference equality used to compare arrays
    
    ArrayFillIncompatibleType

    Arrays.fill(Object[], Object) called with incompatible types.
    
    ArrayHashCode

    hashcode method on array does not hash array contents
    
    ArrayToString

    Calling toString on an array does not provide useful information
    
    ArraysAsListPrimitiveArray

    Arrays.asList does not autobox primitive arrays, as one might expect.
    
    AsyncCallableReturnsNull

    AsyncCallable should not return a null Future, only a Future whose result is null.
    
    AsyncFunctionReturnsNull

    AsyncFunction should not return a null Future, only a Future whose result is null.
    
    AutoValueConstructorOrderChecker

    Arguments to AutoValue constructor are in the wrong order
    
    BadShiftAmount

    Shift by an amount that is out of range
    
    BundleDeserializationCast

    Object serialized in Bundle may have been flattened to base type.
    
    ChainingConstructorIgnoresParameter

    The called constructor accepts a parameter with the same name and type as one of its caller's parameters, but its caller doesn't pass that parameter to it. It's likely that it was intended to.
    
    CheckReturnValue

    Ignored return value of method that is annotated with @CheckReturnValue
    
    CollectionIncompatibleType

    Incompatible type as argument to Object-accepting Java collections method
    
    ComparableType

    Implementing 'Comparable' where T is not compatible with the implementing class.
    
    ComparisonOutOfRange

    Comparison to value that is out of range for the compared type
    
    CompatibleWithAnnotationMisuse

    @CompatibleWith's value is not a type argument.
    
    CompileTimeConstant

    Non-compile-time constant expression passed to parameter with @CompileTimeConstant type annotation.
    
    ComplexBooleanConstant

    Non-trivial compile time constant boolean expressions shouldn't be used.
    
    ConditionalExpressionNumericPromotion

    A conditional expression with numeric operands of differing types will perform binary numeric promotion of the operands; when these operands are of reference types, the expression's result may not be of the expected type.
    
    ConstantOverflow

    Compile-time constant expression overflows
    
    DaggerProvidesNull

    Dagger @Provides methods may not return null unless annotated with @Nullable
    
    DeadException

    Exception created but not thrown
    
    DeadThread

    Thread created but not started
    
    DoNotCall

    This method should not be called.
    
    EqualsNaN

    == NaN always returns false; use the isNaN methods instead
    
    EqualsReference

    == must be used in equals method to check equality to itself or an infinite loop will occur.
    
    ForOverride

    Method annotated @ForOverride must be protected or package-private and only invoked from declaring class, or from an override of the method
    
    FormatString

    Invalid printf-style format string
    
    FormatStringAnnotation

    Invalid format string passed to formatting method.
    
    FunctionalInterfaceMethodChanged

    Casting a lambda to this @FunctionalInterface can cause a behavior change from casting to a functional superinterface, which is surprising to users. Prefer decorator methods to this surprising behavior.
    
    FuturesGetCheckedIllegalExceptionType

    Futures.getChecked requires a checked exception type with a standard constructor.
    
    GetClassOnAnnotation

    Calling getClass() on an annotation may return a proxy class
    
    GetClassOnClass

    Calling getClass() on an object of type Class returns the Class object for java.lang.Class; you probably meant to operate on the object directly
    
    GuardedBy

    Checks for unguarded accesses to fields and methods with @GuardedBy annotations
    
    GuiceAssistedInjectScoping

    Scope annotation on implementation class of AssistedInject factory is not allowed
    
    GuiceAssistedParameters

    A constructor cannot have two @Assisted parameters of the same type unless they are disambiguated with named @Assisted annotations.
    
    GuiceInjectOnFinalField

    Although Guice allows injecting final fields, doing so is disallowed because the injected value may not be visible to other threads.
    
    HashtableContains

    contains() is a legacy method that is equivalent to containsValue()
    
    IdentityBinaryExpression

    A binary expression where both operands are the same is usually incorrect.
    
    Immutable

    Type declaration annotated with @Immutable is not immutable
    
    ImmutableModification

    Modifying an immutable collection is guaranteed to throw an exception and leave the collection unmodified
    
    IncompatibleArgumentType

    Passing argument to a generic method with an incompatible type.
    
    IndexOfChar

    The first argument to indexOf is a Unicode code point, and the second is the index to start the search from
    
    InexactVarargsConditional

    Conditional expression in varargs call contains array and non-array arguments
    
    InfiniteRecursion

    This method always recurses, and will cause a StackOverflowError
    
    InjectMoreThanOneScopeAnnotationOnClass

    A class can be annotated with at most one scope annotation.
    
    InvalidPatternSyntax

    Invalid syntax used for a regular expression
    
    InvalidTimeZoneID

    Invalid time zone identifier. TimeZone.getTimeZone(String) will silently return GMT instead of the time zone you intended.
    
    IsInstanceOfClass

    The argument to Class#isInstance(Object) should not be a Class
    
    IsLoggableTagLength

    Log tag too long, cannot exceed 23 characters.
    
    JUnit3TestNotRun

    Test method will not be run; please correct method signature (Should be public, non-static, and method name should begin with "test").
    
    JUnit4ClassAnnotationNonStatic

    This method should be static
    
    JUnit4SetUpNotRun

    setUp() method will not be run; please add JUnit's @Before annotation
    
    JUnit4TearDownNotRun

    tearDown() method will not be run; please add JUnit's @After annotation
    
    JUnit4TestNotRun

    This looks like a test method but is not run; please add @Test and @Ignore, or, if this is a helper method, reduce its visibility.
    
    JUnitAssertSameCheck

    An object is tested for reference equality to itself using JUnit library.
    
    JavaxInjectOnAbstractMethod

    Abstract and default methods are not injectable with javax.inject.Inject
    
    LiteByteStringUtf8

    This pattern will silently corrupt certain byte sequences from the serialized protocol message. Use ByteString or byte[] directly
    
    LoopConditionChecker

    Loop condition is never modified in loop body.
    
    MislabeledAndroidString

    Certain resources in android.R.string have names that do not match their content
    
    MissingSuperCall

    Overriding method is missing a call to overridden super method
    
    MisusedWeekYear

    Use of "YYYY" (week year) in a date pattern without "ww" (week in year). You probably meant to use "yyyy" (year) instead.
    
    MockitoCast

    A bug in Mockito will cause this test to fail at runtime with a ClassCastException
    
    MockitoUsage

    Missing method call for verify(mock) here
    
    ModifyingCollectionWithItself

    Using a collection function with itself as the argument.
    
    MoreThanOneInjectableConstructor

    This class has more than one @Inject-annotated constructor. Please remove the @Inject annotation from all but one of them.
    
    MustBeClosedChecker

    The result of this method must be closed.
    
    NCopiesOfChar

    The first argument to nCopies is the number of copies, and the second is the item to copy
    
    NonCanonicalStaticImport

    Static import of type uses non-canonical name
    
    NonFinalCompileTimeConstant

    @CompileTimeConstant parameters should be final or effectively final
    
    NonRuntimeAnnotation

    Calling getAnnotation on an annotation that is not retained at runtime.
    
    NullTernary

    This conditional expression may evaluate to null, which will result in an NPE when the result is unboxed.
    
    OptionalEquality

    Comparison using reference equality instead of value equality
    
    OverlappingQualifierAndScopeAnnotation

    Annotations cannot be both Scope annotations and Qualifier annotations: this causes confusion when trying to use them.
    
    OverridesJavaxInjectableMethod

    This method is not annotated with @Inject, but it overrides a method that is annotated with @javax.inject.Inject. The method will not be Injected.
    
    PackageInfo

    Declaring types inside package-info.java files is very bad form
    
    PreconditionsCheckNotNull

    Literal passed as first argument to Preconditions.checkNotNull() can never be null
    
    PreconditionsCheckNotNullPrimitive

    First argument to Preconditions.checkNotNull() is a primitive rather than an object reference
    
    PredicateIncompatibleType

    Using ::equals as an incompatible Predicate; the predicate will always return false
    
    PrivateSecurityContractProtoAccess

    Access to a private protocol buffer field is forbidden. This protocol buffer carries a security contract, and can only be created using an approved library. Direct access to the fields is forbidden.
    
    ProtoFieldNullComparison

    Protobuf fields cannot be null
    
    ProtocolBufferOrdinal

    To get the tag number of a protocol buffer enum, use getNumber() instead.
    
    ProvidesMethodOutsideOfModule

    @Provides methods need to be declared in a Module to have any effect.
    
    RandomCast

    Casting a random number in the range [0.0, 1.0) to an integer or long always results in 0.
    
    RandomModInteger

    Use Random.nextInt(int). Random.nextInt() % n can have negative results
    
    RectIntersectReturnValueIgnored

    Return value of android.graphics.Rect.intersect() must be checked
    
    RestrictedApiChecker

    Check for non-whitelisted callers to RestrictedApiChecker.
    
    ReturnValueIgnored

    Return value of this method must be used
    
    SelfAssignment

    Variable assigned to itself
    
    SelfComparison

    An object is compared to itself
    
    SelfEquals

    Testing an object for equality with itself will always be true.
    
    ShouldHaveEvenArgs

    This method must be called with an even number of arguments.
    
    SizeGreaterThanOrEqualsZero

    Comparison of a size >= 0 is always true, did you intend to check for non-emptiness?
    
    StreamToString

    Calling toString on a Stream does not provide useful information
    
    StringBuilderInitWithChar

    StringBuilder does not have a char constructor; this invokes the int constructor.
    
    SuppressWarningsDeprecated

    Suppressing "deprecated" is probably a typo for "deprecation"
    
    ThrowIfUncheckedKnownChecked

    throwIfUnchecked(knownCheckedException) is a no-op.
    
    ThrowNull

    Throwing 'null' always results in a NullPointerException being thrown.
    
    TruthSelfEquals

    isEqualTo should not be used to test an object for equality with itself; the assertion will never fail.
    
    TryFailThrowable

    Catching Throwable/Error masks failures from fail() or assert*() in the try block
    
    TypeParameterQualifier

    Type parameter used as type qualifier
    
    UnnecessaryTypeArgument

    Non-generic methods should not be invoked with type arguments
    
    UnusedAnonymousClass

    Instance created but never used
    
    UnusedCollectionModifiedInPlace

    Collection is modified in place, but the result is not used
    
    Список проверок

    Не надо читать
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72. Пример 3
    Все животные равны
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73. Object[] a = new Object[]{1, 2, 3};
    Object[] b = new Object[]{1, 2, 3};
    if (a.equals(b)) {
    System.out.println("arrays are equal!");
    }
    Error:(14, 27) java: [ArrayEquals] Reference equality used
    to compare arrays
    (see http:!//errorprone.info/bugpattern/ArrayEquals)
    Did you mean 'if (Arrays.equals(a, b)) {'?
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74. Object[] a = new Object[]{1, 2, 3};
    Object[] b = new Object[]{1, 2, 3};
    if (a.equals(b)) {
    System.out.println("arrays are equal!");
    }
    Error:(14, 27) java: [ArrayEquals] Reference equality used
    to compare arrays
    (see http:!//errorprone.info/bugpattern/ArrayEquals)
    Did you mean 'if (Arrays.equals(a, b)) {'?
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75. Object[] a = new Object[]{1, 2, 3};
    Object[] b = new Object[]{1, 2, 3};
    if (a.equals(b)) {
    System.out.println("arrays are equal!");
    }
    Error:(14, 27) java: [ArrayEquals] Reference equality used
    to compare arrays
    (see http:!//errorprone.info/bugpattern/ArrayEquals)
    Did you mean 'if (Arrays.equals(a, b)) {'?
    75
    

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76. Пример 4

    No toString() attached
    76
    

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77. int[] a = {1, 2, 3};
    System.out.println("array a = " + a);
    77
    

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78. int[] a = {1, 2, 3};
    System.out.println("array a = " + a);
    Error:(23, 43) java: [ArrayToString] Calling toString
    on an array does not provide useful information
    (see http:!//errorprone.info/bugpattern/
    ArrayToString)
    Did you mean 'System.out.println("array a = " +
    Arrays.toString(a));’?
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79. int[] a = {1, 2, 3};
    System.out.println("array a = " + a);
    Error:(23, 43) java: [ArrayToString] Calling toString
    on an array does not provide useful information
    (see http:!//errorprone.info/bugpattern/
    ArrayToString)
    Did you mean 'System.out.println("array a = " +
    Arrays.toString(a));’?
    79
    

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80. Пример 5
    Форматировал, форматировал, 

    да не отфармотировал
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81. PrintStream out = System.out;
    out.println(String.format("Hello, %s%s", "World!"));
    out.println(String.format("Hello, $s", “World!"));
    81
    

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82. PrintStream out = System.out;
    out.println(String.format("Hello, %s%s", "World!"));
    out.println(String.format("Hello, $s", “World!"));
    Error:(14, 39) java: [FormatString] missing argument
    for format specifier '%s'
    (see http:!//errorprone.info/bugpattern/
    FormatString)
    Error:(15, 39) java: [FormatString] extra format
    arguments: used 0, provided 1
    (see http:!//errorprone.info/bugpattern/
    FormatString)
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83. PrintStream out = System.out;
    out.println(String.format("Hello, %s%s", "World!"));
    out.println(String.format("Hello, $s", “World!"));
    Error:(14, 39) java: [FormatString] missing argument
    for format specifier '%s'
    (see http:!//errorprone.info/bugpattern/
    FormatString)
    Error:(15, 39) java: [FormatString] extra format
    arguments: used 0, provided 1
    (see http:!//errorprone.info/bugpattern/
    FormatString)
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84. Уровень 2
    Аннотировал, починил и забыл
    84
    

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85. Уровень 2
    • Придется немного поработать
    • Результаты того стоят
    85
    

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86. Пример 6
    86
    

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87. public class SelfSynchronized {
    @GuardedBy(“this")
    private final List lst = new ArrayList!<>();
    public synchronized void add(final int x) {
    lst.add(x);
    }
    public int size() {
    return lst.size();
    }
    !!...
    Error:(19, 16) java: [GuardedBy] This access should be guarded
    by 'this', which is not currently held
    (see http:!//errorprone.info/bugpattern/GuardedBy)
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88. public class SelfSynchronized {
    @GuardedBy(“this")
    private final List lst = new ArrayList!<>();
    public synchronized void add(final int x) {
    lst.add(x);
    }
    public int size() {
    return lst.size();
    }
    !!...
    Error:(19, 16) java: [GuardedBy] This access should be guarded
    by 'this', which is not currently held
    (see http:!//errorprone.info/bugpattern/GuardedBy)
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89. public class SelfSynchronized {
    @GuardedBy(“this")
    private final List lst = new ArrayList!<>();
    public synchronized void add(final int x) {
    lst.add(x);
    }
    public synchronized int size() {
    return lst.size();
    }
    !!...
    Error:(19, 16) java: [GuardedBy] This access should be guarded
    by 'this', which is not currently held
    (see http:!//errorprone.info/bugpattern/GuardedBy)
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90. Пример 7
    Пожалуйста, закрывайте двери
    90
    

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91. private static class Resource implements AutoCloseable {
    @MustBeClosed
    public Resource() {}
    @Override
    public void close() throws Exception {}
    …
    }
    public void doWorkWithResource() {
    final Resource r = new Resource();
    r.doWork();
    }
    Error:(39, 28) java: [MustBeClosedChecker] The result of this
    method must be closed.
    (see http:!//errorprone.info/bugpattern/MustBeClosedChecker)
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92. private static class Resource implements AutoCloseable {
    @MustBeClosed
    public Resource() {}
    @Override
    public void close() throws Exception {}
    …
    }
    public void doWorkWithResource() {
    final Resource r = new Resource();
    r.doWork();
    }
    Error:(39, 28) java: [MustBeClosedChecker] The result of this
    method must be closed.
    (see http:!//errorprone.info/bugpattern/MustBeClosedChecker)
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93. Уровень 3
    93
    WARNING => ERROR
    

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94. Преимущества ErrorProne
    • Его нельзя проигнорировать
    • Очень низкий уровень false positive
    • Можно постепенно “закручивать” гайки
    • Бесплатный как “бесплатное пиво”
    94
    

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95. Заключение
    95
    

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96. Что с этим делать?
    1. Обсудить доклад с разработчиками
    2. Использовать EqualsVerifier для проверки ваших equals()
    и hashCode()
    3. Включить ErrorProne для поиска гадких ошибок
    4. Аннотировать ваш код для усиления проверок ErrorProne
    96
    

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97. Контакты
    https://www.linkedin.com/in/asatarin

    

    https://twitter.com/asatarin

    

    [email protected]
    97
    

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98. Ссылки
    • http://jqno.nl/equalsverifier/
    • “Not all equals methods are created equal” by Jan Ouwens

    https://youtu.be/pNJ_O10XaoM
    • https://www.artima.com/lejava/articles/equality.html
    • http://www.drdobbs.com/jvm/java-qa-how-do-i-correctly-implement-th/
    184405053
    98
    

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99. Ссылки
    • http://errorprone.info/
    • https://github.com/google/auto/blob/master/value/userguide/index.md
    99
    

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