Automation for the people: Continual refactoring

Using static analysis tools to identify code smells

 

Over the years, I've seen lots of source code from many projects,ranging from elegant designs to code that appeared to be bundledtogether with duct tape. I've written new code and maintained otherdevelopers' source code. I'd rather write new code, but I enjoy takingsome existing code and reducing complexity in a method or extractingduplicate code into a common class. Earlier in my career, many believedthat if you weren't writing new code, you weren't being productive.Fortunately, in the late 1990s, Martin Fowler's book Refactoring (see Resources) helped make the practice of improving existing code without changing external behavior — well — cool.

Much of what I cover in this series is about efficiency:how to reduce the redundancy of time-consuming processes and performthem more quickly. I'll do the same for the tasks I cover in thisarticle and discuss how to perform them more effectively.

About this series

Asdevelopers, we work to automate processes for end-users; yet, many ofus overlook opportunities to automate our own development processes.To that end, Automation for the people is a series of articles dedicated to exploringthe practical uses of automating software development processes and teaching you when and how to apply automation successfully.

Atypical approach to refactoring is to make small changes to existingcode while you're introducing new code or changing a method. Thechallenges of this technique are that it's often inconsistently appliedamong developers on a team, and that it can be easy to missopportunities for refactoring. This is why I advocate using staticanalysis tools to identify coding violations. With them, you gainvisibility into the code base as a whole, and at the class or methodlevel. Fortunately, in Java™ programming, you can choose from anabundance of freely available open source static analysis tools:CheckStyle, PMD, FindBugs, JavaNCSS, JDepend, and many others.

In this article, you'll learn how to:

• Reduce conditional complexity code smells by measuring cyclomatic complexity using CheckStyle and providing refactorings such as Replace Conditional with Polymorphism
  
• Remove duplicated code code smells by assessing code duplication using CheckStyle and providing refactorings such as Pull Up Method
  
• Thin large class code smells by counting source lines of code using PMD (or JavaNCSS) and providing refactorings such as Extract Method
  
• Wipe out too many imports code smells by determining a class's efferent coupling using CheckStyle (or JDepend) and providing refactorings such as Move Method

I'll use the following general format as we examine each code smell:

1. Describe the smell that can indicate a problem in the code
2. Define the measure that can find that smell
3. Show the tool that measures the code smell
4. Present the refactoring and, in some cases, the patterns to fix the code smell

Inessence, this approach provides a framework for finding and fixing codeproblems throughout the code base. And you'll be better informed aboutthe riskier parts of the code base prior to making changes. Better yet,I'll show you how you integrate this approach into automated builds.

Does your code smell?

A code smell is simply a hintthat something could be wrong. Like patterns, code smells provide acommon vocabulary that you can use to identify these types of potentialissues quickly. An actual demonstration of code smells in anarticle is challenging because it could take so many lines of code thatit would lengthen the article excessively. So I'll illustrate somesmells and let you extrapolate the rest based on your experiences inviewing particularly smelly code.

Conditional complexity

Smell: Conditional complexity

Measure: Cyclomatic complexity

Tool: CheckStyle, JavaNCSS, and PMD

Refactorings: Replace Conditional with Polymorphism, Extract Method

Smell

Conditional complexitycan manifest in several different ways in source code. One example ofthis code smell is to have multiple conditional statements such as if, while, or for statements. Another type of conditional complexity can be in the form of switch statements, as demonstrated in Listing 1:

Listing 1. Using a switch statement to perform conditional behavior

...
switch (beerType) {
  case LAGER:  
    System.out.println("Ingredients are..."); 
...
break;
  case BROWNALE:
    System.out.println("Ingredients are..."); 
...
break;
  case PORTER  
    System.out.println("Ingredients are..."); 
...
break;
  case STOUT:
    System.out.println("Ingredients are..."); 
...
break;
  case PALELAGER:
    System.out.println("Ingredients are..."); 
...
break;
  ...
  default:
    System.out.println("INVALID."); 
...
break;
}
...

 

switch statementsthemselves are not a bad thing. But when each statement includes toomany choices and too much code, it could be an indication of code thatneeds to refactored.

Measure

To determine the conditional-complexity code smell, you determine a method's cyclomatic complexity.Cyclomatic complexity is a measure that dates back to 1975 as definedby Thomas McCabe. The Cyclomatic Complexity Number (CCN) measures thenumber of unique paths in a method. Each method starts with a CCN of 1regardless of how many paths are in the method. Conditional constructssuch as if, switch, while, and forstatements are each given a value of 1, along with exception paths. Theoverall CCN for a method is an indication of its complexity. Manyconsider a CCN of 10 or more to indicate an overly complex method.

Tool

CheckStyle, JavaNCSS, and PMD are open source tools that measurecyclomatic complexity. Listing 2 shows a snippet of a CheckStyle rulesfile defined in XML. The CyclomaticComplexity module defines the maximum CCN for a method.

Listing 2. Configuring CheckStyle to find methods with a cyclomatic complexity of 10 or greater

<module name="CyclomaticComplexity">
  <property name="max" value="10"/>
</module>

 

Using the CheckStyle rules filefrom Listing 2, the Gant example in Listing 3 demonstrates how to runCheckStyle as part of an automated build. Gant is an automated buildtool that provides an expressive programming language with support forbuild dependencies. Developers write Gant scripts using the power ofthe Groovy programming language. Because Gant provides full access toAnt's API, anything you can run in Ant can be run from a Gant script.(See the "Build software with Gant" tutorial to learn about Gant.)

Listing 3. Using a Gant script to execute CheckStyle checks

target(findHighCcn:"Finds method with a high cyclomatic complexity number"){
  Ant.mkdir(dir:"target/reports")
  Ant.taskdef(name:"checkstyle", 
    classname:"com.puppycrawl.tools.checkstyle.CheckStyleTask",
    classpathref:"build.classpath")
  Ant.checkstyle(shortFilenames:"true", config:"config/checkstyle/cs_checks.xml", 
    failOnViolation:"false", failureProperty:"checks.failed", classpathref:"libdir") {
    formatter(type:"xml", tofile:"target/reports/checkstyle_report.xml")
    formatter(type:"html", tofile:"target/reports/checkstyle_report.html")
    fileset(dir:"src"){
      include(name:"**/*.java")
    }
  }
}  

 

The Gant script in Listing 3creates the CheckStyle report shown in Figure 1. The bottom of thefigure indicates the CheckStyle cyclomatic-complexity violation for amethod.

Figure 1. CheckStyle report indicating a method failure based on a high CCN

Refactoring

Figure 2 is a UML representation of the Replace Conditional with Polymorphism refactoring:

Figure 2. Replacing conditional statements with polymorphism

See the full figure here.

In Figure 2, I:

1. Create a Java interface called BeerType
2. Define a generic showIngredients() method
3. Create implementing classes for each of the BeerTypes

Forbrevity, I provided one method implementation per class. Ostensibly,you would have more than one method when creating an interface.Refactorings such as Replace Conditional with Polymorphism and ExtractMethod (which I'll explain later in the article) help make code mucheasier to maintain.

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Duplicated code

Smell: Duplicated code

Measure: Code duplication

Tool: CheckStyle, PMD

Refactorings: Extract Method, Pull Up Method, Form Template Method, Substitute Algorithm

Smell

Duplicatecode can creep into a code base unbeknownst to anyone. Sometimes, it'seasier to copy and paste some code than to generalize the behavior intoanother class. One problem with copy-and-paste is that it forces anawareness of multiple copies of the code and the need to maintain them.A more insidious problem occurs when slight variations to the copiedcode cause inconsistent behavior, depending on which method isexecuting the behavior. Listing 4 is an example of code that closes adatabase connection, with the same code present in two methods:

Listing 4. Duplicate code

public Collection findAllStates(String sql) {
...
  try {
    if (resultSet != null) {
      resultSet.close();
    }
    if (stmt != null) {
      stmt.close();
    }
    if (conn != null) {
     conn.close();
   } 
   catch (SQLException se) {
     throw new RuntimeException(se);
   }
 }
...
}
...
public int create(String sql, Beer beer) {
...
  try {
    if (resultSet != null) {
      resultSet.close();
    }
    if (stmt != null) {
      stmt.close();
    }
    if (conn != null) {
     conn.close();
   } 
   catch (SQLException se) {
     throw new RuntimeException(se);
   }
 }
...
}

 

I've got a better IDE

AlthoughI've used Gant in this article's examples to run tools for findingcertain smells, you can also use your IDE to uncover these problems.The Eclipse IDE has plug-ins for many static analysis tools. But Istill recommend that you use an automated build tool so that you canrun integration builds in other environments without the use of an IDE.

Measure

Themeasure for finding duplicated code is to search for code duplicationwithin classes and among other classes in the code base. Duplicationamong classes is more difficult to assess without the help of a tool.Because of the slight changes that copied code can often undergo, it'simportant to measure code that is not simply copied verbatim, but alsocode that is similar.

Tool

PMD'sCopy/Paste Detector (CPD) and CheckStyle are two of the open sourcetools available for finding similar code throughout a Java code base.The CheckStyle configuration file example in Listing 5 demonstrates theuse of the StrictDuplicateCode module:

Listing 5. Using CheckStyle to find at least 10 lines of duplicate code

<module name="StrictDuplicateCode">
  <property name="min" value="10"/>
</module>

 

The min property inListing 5 sets the minimum number of duplicate lines that CheckStylewill flag for review. In this case, it will only indicate blocks ofcode that have at least 10 lines that are similar or have beenduplicated.

Figure 3 shows the results of the module settings from Listing 5 after the automated build runs:

Figure 3. CheckStyle report indicating excessive code duplication

Refactoring

In Listing 6, I take the duplicated code in Listing 4 and reduce the duplication by using the Pull Up Method refactoring — extracting behavior from a larger method into an abstract class method:

Listing 6. Pull Up Method

...
} finally {
  closeDbConnection(rs, stmt, conn);
}
...

 

Don't forget to write tests

Wheneveryou change existing code, you must write corresponding automated testsusing a framework such as JUnit. There is a risk in modifying existingcode; one way to minimize it is to verify through testing that thebehavior works now and in the future.

Duplicated code will happen. I would never recommend to a team to set the unrealistic goal of having noduplication whatsoever. However, an appropriate goal is to ensure thatduplicate code within the code base does not increase. By using astatic analysis tool such as PMD's CPD or CheckStyle, you can determineareas of high code duplication on a continual basis as part of runningan automated build.

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Long method (and large class)

Smell: Long method (and large class)

Measure: Source lines of code (SLOC)

Tool: PMD, JavaNCSS, CheckStyle

Refactorings: Extract Method, Replace Temp with Query, Introduce Parameter Object, Preserve Whole Object, Replace Method with Method Object

Smell

Ageneral rule of thumb I try to adhere to is to keep my methods to 20lines of code or fewer. Of course, there may be exceptions to thisrule, but if I've got methods over 20 lines, I want to know about it.Often, there's a correlation between long methods and conditionalcomplexity. And there's a connection between large classes and longmethods. I'd love to show the example of the 2,200-line method I foundon a project I had to maintain. I printed an entire class containing25,000 lines of code and asked my colleagues to find the bugs. Let'sjust say I made my point as I rolled the printed code down the hallway.

The highlighted section in Listing 7 shows a small portion of an example of a long method code smell:

Listing 7. Long method code smell

public void saveLedgerInformation() {
...
try {
  if (ledger.getId() != null && filename == null) {
    getLedgerService().saveLedger(ledger);
  } else {
    accessFiles().decompressFiles(files, filenames);
  } 
  if (!files.get(0).equals(upload)) {
    upload = files.get(0);
    filename = filenames.get(0);
  }
  if (invalidFiles.isUnsupported(filename)) {
    setError(fileName, message.getMessage());
  } else {
  LedgerFile entryFile = accessFiles().add(upload, filename);
  if (fileType != null && FileType.valueOf(fileType) != null) {
    entryFile.setFileType(FileType.valueOf(fileType));
  }
  getFileManagementService().saveLedger(ledger, entryFile);
  if (!FileStatus.OPENED.equals(entryFile.getFileStatus())) {
    getFileManagementService().importLedgerDetails(ledger);
  }
  if (uncompressedFiles.size() > 1) {
    Helper.saveMessage(getText("ledger.file"));
  }
  
  if (user.getLastName() != null) {
    SearchInfo searchInfo = ServiceLocator.getSearchInfo();
    searchInfo.setLedgerInfo(null);
    isValid = false;
    setDefaultValues();
    resetSearchInfo();
    if (searchInfoValid && ledger != null) {
      isValid = true;
    }
  }
  
} catch (InvalidDataFileException e) {
  ResultType result = e.getResultType();
  for (ValidationMessage message : result.getMessages()) {
    setError(fileName, message.getMessage());
  }
  ledger.setEntryFile(null);


} ...

 

Measure

TheSLOC measure has been misused in years past as an indication ofproductivity. We all know, though, that it's not necessarily true thatthe more lines you write, the better. However, SLOC can be a usefulmeasure when it comes to complexity. The more lines in a method (orclass), the more likely it will be difficult to maintain the code inthe future.

Tool

The script in Listing 8 finds SLOC measures for long methods (and, optionally, large classes):

Listing 8. Gant script to identify large classes and methods

target(findLongMethods:"runs static code analysis"){
 Ant.mkdir(dir:"target/reports")
 Ant.taskdef(name:"pmd", classname:"net.sourceforge.pmd.ant.PMDTask",
   classpathref:"build.classpath")
 Ant.pmd(shortFilenames:"true"){
   codeSizeRules.each{ rfile ->
    ruleset(rfile)
   }
   formatter(type:"xml", tofile:"target/reports/pmd_report.xml")
   formatter(type:"html", tofile:"target/reports/pmd_report.html")
   fileset(dir:"src"){
     include(name:"**/*.java")
   }
  }  
}

 

Once again, I'm using Gant toaccess the Ant API to run Ant tasks. In Listing 8, I'm calling the PMDstatic analysis tool to search for long methods in the code base. PMD(along with JavaNCSS and CheckStyle) can also be used to find longmethods, large classes, and many other code smells.

Refactoring

Listing 9 shows an example of the Extract Method refactoring to reduce the long method smell in Listing 7. After extracting behavior from the method in Listing 7 to the code in Listing 9, I can call the newly created isUserValid() method from the saveLedgerInformation() method in Listing 7:

Listing 9. Extract Method refactoring

private boolean isUserValid(User user) {
  boolean isValid = false;
  if (user.getLastName() != null) {
    SearchInfo searchInfo = ServiceLocator.getSearchInfo();
    searchInfo.setLedgerInfo(null);
    setDefaultValues();
    resetSearchInfo();
    if (searchInfoValid && ledger != null) {
      isValid = true;
    }
  }
  return isValid;
}

 

Often, long methods and largeclasses are indications of other code smells, such as conditionalcomplexity and duplicated code. By finding these methods and classes,you can fix other problems.

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Too many imports

Smell: Too many imports

Measure: Efferent coupling (fan-out per class)

Tool: CheckStyle

Refactorings: Move Method, Extract Class

Smell

Too many importsis an indication that a class relies on too many other classes. You'llnotice you've got this code smell when a change to one classnecessitates making changes to many other classes, because they are sotightly coupled to the class you are changing. The multiple imports inListing 10 are an example:

Listing 10. Multiple imports in a class

import com.integratebutton.search.SiteQuery;
import com.integratebutton.search.OptionsQuery;
import com.integratebutton.search.UserQuery;
import com.integratebutton.search.VisitsQuery;
import com.integratebutton.search.SiteQuery;
import com.integratebutton.search.DateQuery;
import com.integratebutton.search.EvaluationQuery;
import com.integratebutton.search.RangeQuery
import com.integratebutton.search.BuildingQuery;
import com.integratebutton.search.IPQuery;
import com.integratebutton.search.SiteDTO;
import com.integratebutton.search.UrlParams;
import com.integratebutton.search.SiteUtil;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.log4j.Logger;
...

 

Measure

A way to find a class with too much responsibility is through the efferent coupling measure, also referred to as fan out complexity. Fan out complexity assigns a 1 to every class the analyzed class is dependent on.

Tool

Listing 11 shows an example of using CheckStyle to set the maximum number of fan out complexity:

Listing 11. Setting a maximum fan out complexity with CheckStyle

<module name="ClassFanOutComplexity">
  <property name="max" value="10"/>
</module>

 

Refactoring to patterns

The factory methodpattern is one of many design patterns that you can implement whenapplying a refactoring. The factory method is an approach to creating aclass without needing to define explicitly the actual class you arecreating. This pattern is one technique for making it easier to adhereto interfaces rather than an implementing class. You can apply otherdesign patterns when implementing refactorings based on code smells;see Resources for the link to a book that focuses on this concept.

Refactoring

There are several ways to fix the tight coupling that can occur as a result of too many imports. For code such as Listing 10, these refactorings include the Move Method refactoring: I move methods from the individual *Query classes into a Java interface and define common methods that all Query classes must implement. Then, I use the factory method pattern so that the coupling is with the interface.

Byusing a Gant automated build script to execute the CheckStyle Ant task,I can search my code base for classes that rely on too many otherclasses. When I modify code in these classes, I can implement certainrefactorings such as Move Method along with certain design patterns toimprove the ease of maintenance incrementally.

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Refactor ... early and often

ContinuousIntegration (CI) is the practice of integrating changes often. As it'stypically practiced, an automated CI server, run from a separatemachine, triggers an automated build with every change applied to aproject's version-control repository. To ensure that the build scriptsfrom Listing 3 and Listing 8 are run consistently and with every change to a code base, you'll want to configure a CI server such as Hudson (see Resources). Hudson is distributed as a WAR file that you can drop into any Java Web container.

Because the examples in Listing 3 and Listing 8 use Gant, I'll walk through the steps for configuring the Hudson CI server to run Gant scripts:

1. From the Hudson dashboard, install the Gant plug-in for Hudson by selecting Manage Hudson, followed by Manage Plugins, and then select the Available tab. From this tab, select the Gant plug-in check box and click the Install button.
   
2. Restart the Web container (for example, Tomcat).
   
3. Select Manage Hudson, then Configure System. From the Gant installationsection, enter a unique name and the location of the Groovyinstallation on the machine where Hudson is running. Save the changes.
   
4. Go back to the Dashboard (by selecting the Hudson link) and select an existing Hudson Job, select Configure, click the Add build step button, and select the Invoke Gant script option.

WithHudson configured to run the automated build scripts written in Gant,you can get rapid feedback on measures that are related to code smellssuch as long method and conditional complexity as soon as they areintroduced into the code base.

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Other smells and refactorings

Notall smells have correlating measures. However, static analysis toolscan uncover other smells than the ones I've demonstrated. Table 1 listsexamples of other code smells, tools, and possible refactorings:

Table 1. Other smells and refactorings

SmellTool(s)RefactoringDead codePMDRemove CodeTemporary fieldPMDInline TempInconsistent/uncommunicative namesCheckStyle, PMDRename Method, Rename FieldLong parameter listPMDReplace Parameter with Method, Preserve Whole Object, Introduce Parameter Object

This article provides a pattern of correlating a code smell to ameasure that can be configured to be flagged from an automated staticanalysis tool. You can apply refactorings with or without the use ofcertain design patterns. This gives you a framework for consistentlyfinding and fixing code smells in a repeatable manner. I'm confidentthat the examples in this article will help you use static analysistools to find other types of code smells than the ones I'vedemonstrated.

 

Resources

Learn

• Automation for the people (Paul Duvall, developerWorks): Read the complete series. The "Continuous Inspection" (August 2006) and "Improving code with Eclipse plugins" (January 2007) installments are especially relevant to this article's topic.
  
• Smells to Refactorings: A table of recommended refactorings for specific code smells.
  
• Refactoring: Improving the Design of Existing Code (Martin Fowler, Addison-Wesley Professional, 1999): The seminal book on improving the design of an existing code base.
  
• Alpha List of Refactorings: Martin Fowler's list of refactorings.
  
• Refactoring to Patterns(Joshua Kereviesky, Addison-Wesley Professional, 2004): Applying designpatterns to refactorings to improve code. I got the idea of printingout a large class from one of Josh's talks at Agile 2005 in Denver.
  
• "In pursuit of code quality: Monitoring cyclomatic complexity" (Andrew Glover, IBM developerWorks, March 2006): What to do when code complexity is off the charts.
  
• "In pursuit of code quality: Refactoring with code metrics" (Andrew Glover, IBM developerWorks, May 2006): On-target refactoring with code metrics and the Extract Method pattern.
  
• "Continuous Integration: Improving Software Quality and Reducing Risk" (Paul Duvall et al., Addison-Wesley Signature Series, 2007): Chapter 7, Continuous Inspection, covers many of the tools covered in this article.
  
• "Build software with Gant" (Andrew Glover, developerWorks, May 2008): Read this tutorial to learn how to use Gant for flexible builds.
  
• "(Ant to Gant) automagically" (Andrew Glover, The Disco Blog, April 2008): Generate Gant scripts based on an existing Ant script.
  
• "Gant with Hudson in5 steps" (Andrew Glover, The Disco Blog, May 2008): Configuring the Hudson Continuous Integration server to run a Gant build script.
  
• "In pursuit of code quality: Code quality for software architects" (Andrew Glover, IBM developerWorks, April 2006): Use coupling metrics to support your system architecture.
  
• Browse the technology bookstore for books on these and other technical topics.
  
• developerWorks Java technology zone: Hundreds of articles about every aspect of Java programming.
  

Get products and technologies

• Gant: Download Gant and start building software in a predictable and repeatable manner.
  
• CheckStyle: Download CheckStyle to gather metrics and better assess certain code smells.
  
• PMD: Download PMD to gather metrics and better assess certain code smells.
  
• Hudson: A freely available open source server for Continuous Integration.