This list is auto-generated from our sources. Each bug pattern includes code examples of both positive and negative cases; these examples are used in our regression test suite.
Patterns which are marked Experimental will not be evaluated against your code, unless you specifically configure Error Prone. The default checks are marked On by default, and each release promotes some experimental checks after we’ve vetted them against Google’s codebase.
Reference equality used to compare arrays
hashcode method on array does not hash array contents
Calling toString on an array does not provide useful information
Arrays.asList does not autobox primitive arrays, as one might expect.
AsyncCallable should not return a null Future, only a Future whose result is null.
AsyncFunction should not return a null Future, only a Future whose result is null.
Shift by an amount that is out of range
Object serialized in Bundle may have been flattened to base type.
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.
Ignored return value of method that is annotated with @CheckReturnValue
Incompatible type as argument to Object-accepting Java collections method
Comparison to value that is out of range for the compared type
@CompatibleWith's value is not a type argument.
Non-compile-time constant expression passed to parameter with @CompileTimeConstant type annotation.
Compile-time constant expression overflows
Dagger @Provides methods may not return null unless annotated with @Nullable
Exception created but not thrown
This method should not be called.
== NaN always returns false; use the isNaN methods instead
Switch case may fall through
The stream returned by Files.lines should be closed using try-with-resources
Method annotated @ForOverride must be protected or package-private and only invoked from declaring class, or from an override of the method
Invalid printf-style format string
Invalid format string passed to formatting method.
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.
Futures.getChecked requires a checked exception type with a standard constructor.
Calling getClass() on an annotation may return a proxy class
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
Checks for unguarded accesses to fields and methods with @GuardedBy annotations
Invalid @GuardedBy expression
An object is tested for equality to itself using Guava Libraries
Scope annotation on implementation class of AssistedInject factory is not allowed
A constructor cannot have two @Assisted parameters of the same type unless they are disambiguated with named @Assisted annotations.
Although Guice allows injecting final fields, doing so is disallowed because the injected value may not be visible to other threads.
contains() is a legacy method that is equivalent to containsValue()
Writing "a && a", "a || a", "a & a", or "a | a" is equivalent to "a".
Type declaration annotated with @Immutable is not immutable
Modifying an immutable collection is guaranteed to throw an exception and leave the collection unmodified
Passing argument to a generic method with an incompatible type.
The first argument to indexOf is a Unicode code point, and the second is the index to start the search from
This method always recurses, and will cause a StackOverflowError
A class can be annotated with at most one scope annotation.
A standard cryptographic operation is used in a mode that is prone to vulnerabilities
Invalid syntax used for a regular expression
The argument to Class#isInstance(Object) should not be a Class
Log tag too long, cannot exceed 23 characters.
Test method will not be run; please prefix name with "test"
setUp() method will not be run; Please add a @Before annotation
tearDown() method will not be run; Please add an @After annotation
Test method will not be run; please add @Test annotation
An object is tested for reference equality to itself using JUnit library.
Abstract and default methods are not injectable with javax.inject.Inject
This pattern will silently corrupt certain byte sequences from the serialized protocol message. Use ByteString or byte directly
Loop condition is never modified in loop body.
Certain resources in
android.R.string have names that do not match their content
Switches on enum types should either handle all values, or have a default case.
Use of "YYYY" (week year) in a date pattern without "ww" (week in year). You probably meant to use "yyyy" (year) instead.
A bug in Mockito will cause this test to fail at runtime with a ClassCastException
Missing method call for verify(mock) here
Using a collection function with itself as the argument.
This class has more than one @Inject-annotated constructor. Please remove the @Inject annotation from all but one of them.
Invocations of methods or constructors annotated with @MustBeClosed must occur within the resource variable initializer of a try-with-resources statement, or the return statement of another method annotated with @MustBeClosed.
Static import of type uses non-canonical name
@CompileTimeConstant parameters should be final or effectively final
Comparison using reference equality instead of value equality
Annotations cannot be both Scope annotations and Qualifier annotations: this causes confusion when trying to use them.
Varargs doesn't agree for overridden method
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.
Declaring types inside package-info.java files is very bad form
Literal passed as first argument to Preconditions.checkNotNull() can never be null
First argument to
Preconditions.checkNotNull() is a primitive rather than an object reference
Protobuf fields cannot be null
@Provides methods need to be declared in a Module to have any effect.
Use Random.nextInt(int). Random.nextInt() % n can have negative results
Return value of android.graphics.Rect.intersect() must be checked
Check for non-whitelisted callers to RestrictedApiChecker.
Return value of this method must be used
Variable assigned to itself
An object is compared to itself
Variable compared to itself
An object is tested for equality to itself
Comparison of a size >= 0 is always true, did you intend to check for non-emptiness?
Calling toString on a Stream does not provide useful information
StringBuilder does not have a char constructor; this invokes the int constructor.
Suppressing "deprecated" is probably a typo for "deprecation"
throwIfUnchecked(knownCheckedException) is a no-op.
Throwing 'null' always results in a NullPointerException being thrown.
An object is tested for equality to itself using Truth Libraries.
Catching Throwable/Error masks failures from fail() or assert*() in the try block
Type parameter used as type qualifier
Non-generic methods should not be invoked with type arguments
Instance created but never used
Collection is modified in place, but the result is not used
Method reference is ambiguous
Classes that implement Annotation must override equals and hashCode. Consider using AutoAnnotation instead of implementing Annotation by hand.
Possible sign flip from narrowing conversion
valueOf or autoboxing provides better time and space performance
Mockito cannot mock final classes
Inner class is non-static but does not reference enclosing class
Class.newInstance() bypasses exception checking; prefer getDeclaredConstructor().newInstance()
Implicit use of the platform default charset, which can result in e.g. non-ASCII characters being silently replaced with '?' in many environments
Double-checked locking on non-volatile fields is unsafe
This code, which counts elements using a loop, can be replaced by a simpler library method
Classes that override equals should also override hashCode.
An equality test between objects with incompatible types always returns false
If you return or throw from a finally, then values returned or thrown from the try-catch block will be ignored. Consider using try-with-resources instead.
Classes extending PreferenceActivity must implement isValidFragment such that it does not unconditionally return true to prevent vulnerability to fragment injection attacks.
Subclasses of Fragment must be instantiable via Class#newInstance(): the class must be public, static and have a public nullary constructor
Overloads will be ambiguous when passing lambda arguments
Return value of methods returning Future must be checked.
Calling getClass() on an enum may return a subclass of the enum type
Annotations should always be immutable
Enums should always be immutable
This annotation has incompatible modifiers as specified by its @IncompatibleModifiers annotation
Constructors on abstract classes are never directly @Injected, only the constructors of their subclasses can be @Inject'ed.
Please also override int read(byte, int, int), otherwise multi-byte reads from this input stream are likely to be slow.
Class should not implement both
Floating-point comparison without error tolerance
Test class inherits from JUnit 3's TestCase but has JUnit 4 @Test annotations.
Not calling fail() when expecting an exception masks bugs
method overrides method in supertype; expected @Override
Field is constant (named CONSTANT_CASE), but field type is mutable
Compound assignments to bytes, shorts, chars, and floats hide dangerous casts
This update of a volatile variable is non-atomic
equals method doesn't override Object.equals
Constructors should not be annotated with @Nullable since they cannot return null
@Nullable should not be used for primitive types since they cannot be null
void-returning methods should not be annotated with @Nullable, since they cannot return null
Use grouping parenthesis to make the operator precedence explicit
This method is not annotated with @Inject, but it overrides a method that is annotated with @com.google.inject.Inject. Guice will inject this method, and it is recommended to annotate it explicitly.
Preconditions only accepts the %s placeholder in error message strings
Protobuf fields cannot be null, so this check is redundant
ordinal() value of Protocol Buffer Enum can change if enumeration order is changed
Comparison using reference equality instead of value equality
This annotation is missing required modifiers as specified by its @RequiredModifiers annotation
SimpleDateFormat is not thread-safe, and should not be used as a constant field.
Writes to static fields should not be guarded by instance locks
Synchronizing on non-final fields is not safe: if the field is ever updated, different threads may end up locking on different objects.
Truth Library assert is called on a constant.
Type parameter declaration overrides another type parameter already declared
Declaring a type parameter that is only used in the return type is a misuse of generics: operations on the type parameter are unchecked, it hides unsafe casts at invocations of the method, and it interacts badly with method overload resolution.
Creation of a Set/HashSet/HashMap of java.net.URL. equals() and hashCode() of java.net.URL class make blocking internet connections.
Switch handles all enum values; an explicit default case is unnecessary and defeats error checking for non-exhaustive switches.
Unsynchronized method overrides a synchronized method.
Because of spurious wakeups, Object.wait() and Condition.await() must always be called in a loop
An argument is more similar to a different parameter; the arguments may have been swapped.
@AssistedInject and @Inject cannot be used on the same constructor.
@AutoFactory and @Inject should not be used in the same type.
The source file name should match the name of the top-level class it contains
This comparison method violates the contract
Deprecated item is not annotated with @Deprecated
Division by integer literal zero
Empty statement after if
A scoping annotation's Target should include TYPE and METHOD.
Using more than one qualifier annotation on the same element is not allowed.
Scope annotation on an interface or abstact class is not allowed
Scoping and qualifier annotations must have runtime retention.
Injected constructors cannot be optional nor have binding annotations
jMock tests must have a @RunWith(JMock.class) annotation, or the Mockery field must have a @Rule JUnit annotation
@javax.inject.Inject cannot be put on a final field.
This method does not acquire the locks specified by its @LockMethod annotation
Prefer 'L' to 'l' for the suffix to long literals
@Multibinds is the new way to declare multibindings.
@NoAllocation was specified on this method, but something was found that would trigger an allocation
Calling getAnnotation on an annotation that is not retained at runtime.
Numeric comparison using reference equality instead of value equality
Method parameter has wrong package
Comparing protobuf fields of type String using reference equality
Qualifier applied to a method that isn't a @Provides method. This method won't be used for dependency injection
Static and default methods in interfaces are not allowed in android builds.
This method does not acquire the locks specified by its @UnlockMethod annotation
A different potential argument is more similar to the name of the parameter than the existing argument; this may be an error
Assertions may be disabled at runtime and do not guarantee that execution will halt here; consider throwing an exception instead
@AssistedInject and @Inject should not be used on different constructors in the same class.
BigDecimal(double) and BigDecimal.valueOf(double) may lose precision, prefer BigDecimal(String) or BigDecimal(long)
This code declares a binding for a common value type without a Qualifier annotation.
Empty top-level type declaration
Calls to ExpectedException#expect should always be followed by exactly one statement.
Hardcoded reference to /sdcard
The Google Java Style Guide requires that each switch statement includes a default statement group, even if it contains no code. (This requirement is lifted for any switch statement that covers all values of an enum.)
Static import of member uses non-canonical name
Passing a primitive array to a varargs method is usually wrong
Injection frameworks currently don't understand Qualifiers in TYPE_PARAMETER or TYPE_USE contexts.
Thrown exception is a subtype of another
A static variable or method should not be accessed from an object instance
String comparison using reference equality instead of value equality
Using @Test(expected=…) is discouraged, since the test will pass if any statement in the test method throws the expected exception
Non-constant variable missing @Var annotation
Field name is CONSTANT_CASE, but field is not static and final
@Multibinds is a more efficient and declarative mechanism for ensuring that a set multibinding is present in the graph.
Fields that can be null should be annotated @Nullable
Private methods that do not reference the enclosing instance should be static
C-style array declarations should not be used
Variable declarations should declare only one variable
Source files should not contain multiple top-level class declarations
Package names should match the directory they are declared in
Method parameters that aren't checked for null shouldn't be annotated @Nullable
Add a private constructor to modules that will not be instantiated by Dagger.
Utility classes (only static members) are not designed to be instantiated and should be made noninstantiable with a default constructor.
Methods that can return null should be annotated @Nullable
Unchecked exceptions do not need to be declared in the method signature.
Using static imports for types is unnecessary
@Binds is a more efficient and declarative mechanism for delegating a binding.
Wildcard imports, static or otherwise, should not be used