fb-contrib™: A FindBugs™ auxiliary detector plugin
fb-contrib™ is an extra detector plugin to be used with the static bug finder FindBugs™ (findbugs.sourceforge.net). Just download the fb-contrib.jar file, and place it in your FindBugs™' plugin directory. FindBugs™ will automatically pick up the jar file, and incorporate these detectors with its own.
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Bug Descriptions
Detectors added in SVN- [TBP] Tristate Boolean Pattern
Looks for methods that are defined to return Boolean, but return null. This thus allows three return values, Boolean.FALSE, Boolean.TRUE and null. If three values are intended, it would be more clear to just create an enumeration with three values and return that type. - [SUA] Suspicious Uninitialized Array
Looks for creation of arrays, that are not populated before being returned for a method. While it is possible that the method that called this method will do the work of populated the array, it seems odd that this would be the case. - [ITU] Inappropriate ToString Use
Looks for methods that rely on the format of the string fetched from another object's toString method, when that method appears not to be owned by the author of the calling method. As the implementation of toString() is often considered a private implementation detail of a class, and not something that should be relied on, depending on it's format is dangerous. - [BED] Bogus Exception Declaration
Looks for constructors, private methods or static methods that declare that they throw specific checked exceptions, but that do not. This just causes callers of these methods to do extra work to handle an exception that will never be thrown. - [DTEP] Deprecated Typesafe Enum Pattern
Looks for classes that appear to implement the old style type safe enum pattern that was used before java added Enum support to the language. Since this class is compiled with java 1.5 or later, it would be simpler to just use java enums. - [UNNC] Unnecessary New Null Check
Looks for construction of new objects, and then the immediate testing whether the object is null or not. As the new operator will always succeed, or through an exception, this test is unnecessary and represents a misunderstanding as to how the jvm works.
Detectors added in v3.8.0- [DSOC] Dubious Set of Collections
Looks for sets or keySets of maps that contain other collections. As typically collections calculate their hashCode, equals and compareTo methods by iterating the collection and evaluating the same function on each item in the collection, this can be costly from a performance point of view. In addition, using a set, or keySet of a map, infers that you will be looking for items based on the value of a collection, which seems dubious at best. Finally, as collections are often modified, This may cause problems if the collection is modified, thus changing hashCodes, etc, while the collection is in the set. If you wish to keep a collection of collections, the outer collection should probably be a list to avoid these problems - [IICU] Incorrect Internal Class Use
Looks for classes that use objects from internal sun, xerces or xalan packages. As these are internal to the respective products and subject to change or removal, these should not be used. - [LO] Logger Oddities
Looks for uses of log4j or slf4j where the class specified when creating the logger is not the same as the class in which this logger is used. - [SCSS] Suspicious Clustered Session Support
Looks for methods that access objects in http sessions, that are complex objects, modifies those objects, but does not call setAttribute to signify a change so that cluster replication can happens correctly.
Detectors added in v3.6.0- [CFS] Confusing Function Semantics
Looks for methods that return a parameter after making what looks like modifications to that parameter. This leads to confusion for the user of this method as it isn't obvious that the 'original' object is modified. If the point of this method is to modify the parameter, it is probably better just to have the method be a void method, to avoid confusion. - [SCA] Suspicious Clone Algorithm
Looks for implementation of clone where an assignment is made to a field of the source object. It is likely that that store should have occurred on the cloned object, as the clone operation is almost always considered read only. - [JAO] JUnit Assertion Oddities
Looks for junit test case methods that use assertions with odd parameters. Things such as, passing a constant as the second (actual) parameter, not using the three parameter version of asserts for doubles, or passing true or false as the first parameter instead of using assertTrue, or assertFalse. - [WEM] Weak Exception Messaging
Looks for exceptions that are thrown with static strings as messages. Using static strings doesn't differentiate one use of this method versus another, and so it may be difficult to determine how this exception occurred without showing context.
Detectors added in v3.4.0- [SJVU] Suspicious JDK Version Use
Looks for calls to classes and methods that do not exist in the JDK for which this class is compiled. This can happen if you specify the -source and -target options of the javac compiler, and specify a target that is less than the jdk version of the javac compiler. - [UAA] Use Add All
Looks for loops that transfers the contents of one collection to another. These collection sources might be local variables or member fields, including sets, maps key/values, lists, or arrays. It is simpler to just use the addAll method of the collection class. In the case where the source is an array, you can use Arrays.asList(array), and use that as the source to addAll. - [MRC] Method returns Constant
Looks for private methods that can only return one constant value. Either the class should not return a value, or perhaps a branch was missed. - [NCS] Needless Custom Serialization
Looks for classes that implement Serializable and implements readObject and writeObject by just calling the readDefaultObject or writeDefaultObject of the stream parameter. As this is the standard behavior, implementing these methods is not needed. - [EXS] Exception Softening
looks for methods that catch checked exceptions, and throw unchecked exceptions in their place. There are several levels of concern. Least important are methods constrained by interface or super class contracts not to throw checked exceptions but appear owned by the same author. Next are methods constrained by interface or super class contracts and throw other types of checked exceptions. Lastly are method not constrained by any interface or superclass contract.
Detectors added in v3.2.0- [SCRV] Suspicious Comparator Return Values
Looks for classes that implement Comparator or Comparable, and whose compare or compareTo methods return constant values only, but that don't represent the three possible choices (a negative number, 0, and a positive number). - [SPP] Sillyness Pot Pourri
Looks for various small problems that don't fall into any particular category. - [SCII] Spoiled Child Interface Implementor
Looks for classes that implement interfaces by relying on methods being implemented in superclasses, even though the superclass knows nothing about the interface being implemented by the child. - [DWI] Deleting While Iterating
Looks for deletion of items from a collection using the remove method of the collection at the same time that the collection is being iterated on. If this occurs the iterator will become invalid and throw a ConcurrentModificationException. Instead, the remove should be called on the iterator itself. - [USS] Use String Split
Looks for code that builds an array by using a StringTokenizer to break up a string and place individual elements into an array. It is simpler to use String.split instead.
Detectors added in v3.0.0- [LEST] Lost Exception Stack Trace
Looks for methods that catch exceptions, and rethrow another exception without encapsulating the original exception within it. Doing this loses the stack history, and where the original problem occurred. This makes finding and fixing errors difficult. - [UCPM] Use Character Parameterized Method
Looks for methods that pass single character string constants as parameters to methods that alternatively have an overridden method that accepts a character instead. It is easier for the method to handle a single character than a String. - [TR] Tail Recursion
Looks for methods that make a recursive call to itself as the last statement in the method. This tail recursion could be converted into a simple loop which would improve the performance and stack requirements. - [URV] Unrelated Return Values
Looks for methods that return Object, and who's code body returns two or more different types of objects that are unrelated (other than by Object). - [PIS] Possible Incomplete Synchronization
Looks for classes that don't handle serialization of parent class member fields when the class in question is serializable but is derived from non serializable classes.
Detectors added in v2.8.0Note: This version of fb-contrib requires FindBugs v1.0.0
- [NMCS] Needless Member Collection Synchronization
Looks for private collection members, either static or instance, that are only initialized in the clinit or init, but are synchronized. This is not necessary as the constructor or static initializer are guaranteed to be thread safe. - [ITC] Inheritance Type Checking
Looks for if/else blocks where a series of them use instanceof on the same variable to determine what to do. If these classes are related by inheritance, this often is better handled through calling a single overridden method. - [PRMC] Possibly Redundant Method Calls
Looks for calls of the same method on the same object when that object hasn't changed. This often is redundant, and the second call can be removed, or combined. - [UTA] Use toArray
Looks for code that builds an array of values from a collection, by manually looping over the elements of the collection, and adding them to the array. It is simpler and cleaner to use mycollection.toArray(new type[mycollection.size()].
Detectors added in v2.6.0Note: This version of fb-contrib requires FindBugs v0.9.7.
- [FCBL] Field could be Local
Looks for classes that declare fields that are used in a locals-only fashion, specifically private fields that are accessed first in each method with a store vs. a load. These fields can be declared as one or more locals. - [NOS] Non Owned Synchronization
looks for methods that synchronize on variables that are not owned by the current class. Doing this causes confusion when two classes use the same variable for their own synchronization purposes. For cleanest separation of interests, only synchronize on private fields of the class. Note that 'this' is not owned by the current class and synchronization on 'this' should be avoided as well. - [S508C] Section 508 Compliance
looks for classes and methods that do not support coding styles that allow Accessibility software to make full use of the gui for people with visual impediments. Commonly known as 'Section 508 Compliance' this detector finds a varied list of issues that hamper screen readers, and make color/size adjustments difficult. - [UEC] Use Enum Collections
looks for uses of sets or maps where the key is an enum. In these cases, it is more efficient to use EnumSet or EnumMap. It is a jdk1.5 only detector.
Detectors added in v2.4.0- [DDC] Double Date Compare
Looks for methods that compare two dates using .equals and after or before. This combination of two comparisons can be accomplished with just one comparison. - [JVR] JDBC Vendor Reliance
Looks for uses of jdbc vendor specific classes and methods making the database access code non portable. - [PMB] Possible Memory Bloat
Looks for classes that maintain collections or StringBuffer/StringBuilders in static member variables, and that do not appear to provide a way to clear or remove items from these members. Such class fields are likely causes of memory bloat. - [LSYC] Local Synchronized Collection
looks for allocations of synchronized collections that are stored in local variables, and never stored in fields or returned from methods. As local variables are by definition thread safe, using synchronized collections in this context makes no sense.
Detectors added in v2.2.0Note: fb-contrib v2.2.0 requires FindBugs™ v0.95 or later
- [CLI] Constant List Index
Looks for methods that access an array or list using a constant integer index. Often, this is a typo where a loop variable is intended to be used. If however, specific list indices mean different specific things, then perhaps replacing the list with a first-class object with meaningful accessors would make the code less brittle. - [SCR] Sloppy Class Reflection
Looks for methods that use Class.forName("XXX") to load a class object for a class that is already referenced by this class. It is simpler to just use XXX.class, and doing so protects the integrity of this code from such transformations as obfuscation. Use of Class.forName should only be used when the class in question isn't already statically bound to this context. - [AWCBR] Array Wrapped Call By Reference
Looks for methods that use an array of length one to pass a variable to achieve call by pointer ala C++. It is better to define a proper return class type that holds all the relevant information retrieved from the called method. - [SG] Sluggish Gui
Looks for methods that implement awt or swing listeners and perform time consuming operations. Doing these operations in the gui thread will cause the interface to appear sluggish and non-responsive to the user. It is better to use a separate thread to do the time consuming work so that the user has a better experience. - [NIR] Needless Instance Retrieval
Looks for methods that call a method to retrieve a reference to an object only to then load a static field of that object's class. It is simpler and more performant to just directly load the field from the class itself.
Detectors added in v2.0.0- [ABC] Array Based Collections
Looks for methods that use arrays for items in the keyset of a map, or as an element of a set, or in a list when using the contains method. Since arrays do not, and cannot define an equals method, reference equality is used for these collections, which is probably not desired. If it is, consider using the IdentityHashMap class when using Maps in this case, to better document your intentions. - [ODN] Orphaned DOM Nodes
Looks for methods that create DOM nodes but do not append them to any Document. - [A0M] Abstract Overridden Method
Looks for abstract methods that override a concrete method in a super class. Doing this casts away the implementation of the super class, and breaks the implied contract as set forth by the parent class. - [CBX] Custom Built XML
Looks for methods that build xml based strings by concatenation strings and custom values together. Doing so makes brittle code, that is difficult to modify, validate and understand. It is cleaner to create external xml files that are transformed at runtime, using parameters set through Transformer.setParameter.
Detectors added in v1.8.0- [STS] Spurious Thread States
Finds methods that call wait, notify or notifyAll on an instance of a java.lang.Thread. Since the internal workings of the thread is to synchronize on the thread itself, introducing client calls will confuse the thread state of the object in question, and will cause spurious thread state changes, either waking threads up when not intended, or removing the thread from the runnable state. - [NAB] Needless Autoboxing
Finds methods that pass an instance of a primitive wrapper class, to a constructor of the same class. Since wrapper classes are immutable, you can just use the original instance, instead of creating a new one. This bug is a misuse of autoboxing. - [USBR] UnnecessaryStoreBeforeReturn
Finds methods that store the return result in a local variable, and then immediately returns that local variable. - [COM] CopiedOverriddenMethod
Finds methods that are implemented with an exact copy of their super class method's implementation. In most cases, this means that this method can just be removed.
Detectors added in v1.6.0- [SMII] Static Method Instance Invocation
Finds methods that make static method calls using an instance reference. For documentation purposes, it is better to call the method using the class name. This may represent a change in definition that should be noticed. - [AFBR] Abnormal Finally Block Return
Finds methods that return or throw an exception from a finally block. Since a finally block is executed after any return or throw statements that are present in the try or catch block, these exit values are swallowed by the finally block's actions. - [NCMU] Non Collections Method Use
Finds calls to collections objects using methods that are not defined in the Collections interfaces, but that have equivalent methods defined in such. By using the new methods, it allows for the replacement of concrete classes with interfaces, and simplifies changing collection types if desired. - [CAO] Confusing Autoboxed Overloading
Finds classes that define overloaded methods where the only difference is a parameter being of type java.lang.Character, and int, long, float or double. Due to autoboxing, one might conclude that a parameter of 'a' would autobox to Character, but would instead be cast to a double.
Detectors added in v1.4.0- [FP] Final Parameters
Finds parameters that could be marked as final, but aren't. Doing so helps document the method, keeps unwanted changes to creep in, and may help the jvm jit compiler to optimize better. - [ACEM] Abstract Class Empty Methods
Finds empty methods, or methods that just throw an exception in abstract classes. In these cases, it probably is more correct to just define the method to be abstract as well, so that proper subclass implementation is enforced. - [MAC] Manual Array Copy
Finds methods that copy elements from one array to another manually using a loop. It is better performing to use System.arraycopy, as this method is native. - [FPL] Floating Point Loops
Finds methods that use floating point variables as the index to loops. Since floating point math is inprecise, errors will accumulate each time through the loop, making the logic suspect. It is better to use an integer index, and calculate the desired floating point value from this integer.
Detectors added in v1.2.0- [PL] Parallel Lists
Finds classes that maintain two or more lists or arrays that appear to share a one-to-one relationship through a common index. It is usually better to create a separate class that holds all corresponding attributes, and add instances of this class to just one list or array. - [DLC] Dubious List Collection
Finds fields that are implementations of java.util.List, but that are used in a set-like fashion. Since lookup type operations are performed using a linear search for Lists, the performance for large Lists will be poor. Consideration should be made as to whether these fields should be sets. - [PCOA] Partially Constructed Object Access
Finds constructors that call non-final methods in non-final classes. If this class is derived from, and the method is overridden, then that method will be executing on an object that hasn't been constructed in regards to the subclass implementation. These methods should probably be defined as final. - [LSC] Literal String Comparison
Finds methods that call the equals or compareTo methods on a String variable passing in a String literal. A NullPointerException may occur if the string variable is null. If instead the method was called on the string literal, and the variable was passed as an argument, this exception could never happen
Detectors added in v1.0.0- [OCP] Overly Concrete Parameters
Finds parameters to methods that are defined as concrete classes, when they're usage pattern can be defined by an implemented interface. By switching to the interface, you can reduce coupling, which helps making the code more testable and changeable. - [LII] List Indexed Iterating
Looks for uses of using loop indexed variables to 'iterate' over a List by calling get(i) each time thru the loop. Depending on the List implementation, using Iterators can be significantly faster. Using Iterators also makes it easier to substitute other collection types. - [UCC] Unrelated Collection Contents
Looks for collections that hold objects that are unrelated by class or interface inheritance, other than java.lang.Object. Doing so, leads to brittle code, either by 'encoding' type knowledge in the position of an element, or using instanceof tests. It is usually better to create a separate class, add the individual types as members to it, and add an instance of this class to the collection. - [DRE] Declared Runtime Exception
Finds methods that declare RuntimeExceptions in their throws clause. While not illegal, this may indicate a misunderstanding as to how unchecked exceptions are handled. If is felt that a RuntimeException is so prevalent that it should be declared, it is probably a better idea to prevent the occurance in code.
Detectors added in v0.9.3
- [ISB] Inefficient String Buffering
Finds Concatenation inside of a StringBuffer.append call, which creates temporary StringBuffers. - [SCI] Synchronized Collection Iterators
Finds use of iterators on collections built from Collection.synchronizedXXX() calls. As iterators are by default not multithread safe, there use with a synchronized collections seems dubious. - [CC] Cyclomatic Complexity
Finds methods that are overly complex based on the McCabe algorithm for counting number of unique branches in the method
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