Code smell
Encyclopedia
In computer programming
, code smell is any symptom
in the source code
of a program
that possibly indicates a deeper problem.
Often the deeper problem hinted by a code smell can be uncovered when the code is subjected to a short feedback cycle
where it is refactored
in small, controlled steps, and the resulting design is examined to see if there are any further code smells that indicate the need of more refactoring. From the point of view of a programmer charged with performing refactoring, code smells are heuristics to indicate when to refactor, and what specific refactoring techniques to use. Thus, a code smell is a driver for refactoring.
The term appears to have been coined by Kent Beck
on WardsWiki in the late 1990s. Usage of the term increased after it was featured in Refactoring. Improving the Design of Existing Code.
Code Smell is also a term used by agile
programmers.
Determining what is and is not a code smell is often a subjective judgment, and will often vary by language, developer and development methodology. There are tools, such as Checkstyle
, PMD
and FindBugs
for Java
, to automatically check for certain kinds of code smells.
Computer programming
Computer programming is the process of designing, writing, testing, debugging, and maintaining the source code of computer programs. This source code is written in one or more programming languages. The purpose of programming is to create a program that performs specific operations or exhibits a...
, code smell is any symptom
Symptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
in the source code
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
of a program
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
that possibly indicates a deeper problem.
Often the deeper problem hinted by a code smell can be uncovered when the code is subjected to a short feedback cycle
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
where it is refactored
Refactoring
Code refactoring is "disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior", undertaken in order to improve some of the nonfunctional attributes of the software....
in small, controlled steps, and the resulting design is examined to see if there are any further code smells that indicate the need of more refactoring. From the point of view of a programmer charged with performing refactoring, code smells are heuristics to indicate when to refactor, and what specific refactoring techniques to use. Thus, a code smell is a driver for refactoring.
The term appears to have been coined by Kent Beck
Kent Beck
Kent Beck is an American software engineer and the creator of the Extreme Programming and Test Driven Development software development methodologies. Beck was one of the 17 original signatories of the Agile Manifesto in 2001....
on WardsWiki in the late 1990s. Usage of the term increased after it was featured in Refactoring. Improving the Design of Existing Code.
Code Smell is also a term used by agile
Agile software development
Agile software development is a group of software development methodologies based on iterative and incremental development, where requirements and solutions evolve through collaboration between self-organizing, cross-functional teams...
programmers.
Determining what is and is not a code smell is often a subjective judgment, and will often vary by language, developer and development methodology. There are tools, such as Checkstyle
Checkstyle
Checkstyle is a static code analysis tool used in software development for checking if Java source code complies with coding rules.- Advantages and limits :...
, PMD
PMD (software)
PMD is a static ruleset based Java source code analyzer that identifies potential problems like:* Possible bugs - Empty try/catch/finally/switch blocks.* Dead code - Unused local variables, parameters and private methods....
and FindBugs
FindBugs
FindBugs is an open source program created by Bill Pugh and David Hovemeyer which looks for bugs in Java code. It uses static analysis to identify hundreds of different potential types of errors in Java programs. FindBugs operates on Java bytecode, rather than source code. The software is...
for Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
, to automatically check for certain kinds of code smells.
Common code smells
- Duplicated codeDuplicate codeDuplicate code is a computer programming term for a sequence of source code that occurs more than once, either within a program or across different programs owned or maintained by the same entity. Duplicate code is generally considered undesirable for a number of reasons...
: identical or very similar code exists in more than one location. - Long method: a methodMethod (computer science)In object-oriented programming, a method is a subroutine associated with a class. Methods define the behavior to be exhibited by instances of the associated class at program run time...
, function, or procedure that has grown too large. - Large class: a classClass (computer science)In object-oriented programming, a class is a construct that is used as a blueprint to create instances of itself – referred to as class instances, class objects, instance objects or simply objects. A class defines constituent members which enable these class instances to have state and behavior...
that has grown too large. See God objectGod objectIn object-oriented programming, a God object is an object that knows too much or does too much. The God object is an example of an anti-pattern....
. - Too many parameters: a long list of parameters in a procedure or function make readability and code quality worse.
- Feature envy: a class that uses methods of another class excessively.
- Inappropriate intimacy: a class that has dependencies on implementation details of another class.
- Refused bequest: a class that overrideMethod overriding (programming)Method overriding, in object oriented programming, is a language feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its superclasses or parent classes...
s a method of a base class in such a way that the contract of the base class is not honored by the derived class. See Liskov substitution principleLiskov substitution principleSubstitutability is a principle in object-oriented programming. It states that, in a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S without altering any of the desirable properties of that program...
. - Lazy class / Freeloader: a class that does too little.
- Contrived complexity: forced usage of overly complicated design patternsDesign pattern (computer science)In software engineering, a design pattern is a general reusable solution to a commonly occurring problem within a given context in software design. A design pattern is not a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that...
where simpler design would suffice. - Excessively long identifiers: in particular, the use of naming conventions to provide disambiguation that should be implicit in the software architectureSoftware architectureThe software architecture of a system is the set of structures needed to reason about the system, which comprise software elements, relations among them, and properties of both...
. - Excessively short identifiers: the name of a variable should reflect its function unless it's obvious.
- Excessive use of literals: these should be coded as named constants, to improve readability and to avoid programming errors. Additionally, literals can and should be externalized into resource files/scripts where possible, to facilitate localization of software if it is intended to be deployed in different regions.
See also
- Anti-patternAnti-patternIn software engineering, an anti-pattern is a pattern that may be commonly used but is ineffective and/or counterproductive in practice.The term was coined in 1995 by Andrew Koenig,...
- Category Programming principles
- Category Programming rules of thumb
- List of tools for static code analysis