My talk about Robert C. Martin's book "Clean Code: A Handbook of Agile Software Craftsmanship".

1. Clean Code
Be a little more careful with the code you write!
Ana Cortés Corbalán
05.02.2013

2. What? Why? How?
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3. The only valid measurement of code quality:
WTFs/minute
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4. What is Clean Code?
§ Simple § Efficient
§ No duplications § Elegant
§ Direct § Focused
§ With tests § Minimal dependencies
§ It was written by someone who cares
§ ...
§ Any fool can write code that a computer can
understand. Good programmers write code that
humans can understand. - Martin Fowler
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5. Why is clean code so important?
§ Easier to read
§ Easier to understand
§ Easier to change
§ Add new features
§ Find and fix bugs
§ Cheaper to maintain
§ Code quality is part of software quality
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6. Use Intention-Revealing Names
§ int d;!
§ int days;!
§ int days; //days since creation!
§ int daysSinceCreation;!
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7. Use Intention-Revealing Names
§ What is the purpose?
public List<int[]> getValues() {!
List<int[]> list1 = new ArrayList<int[]>();!
for (int[] x : theList)!
if (x[0] == 4) list1.add(x);!
return list1;!
}!
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8. Use Intention-Revealing Names
§ Better?
!
public List<Cell> getFlaggedCells() {!
List<Cell> flaggedCells = new ArrayList<Cell>();!
for (Cell cell : gameBoard) !
if (cell.isFlagged()) flaggedCells.add(cell);!
return flaggedCells;!
}!
!
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9. Don´t talk in code – Use Pronounceable Names
class DtaRcrd102 {
private Date genymdhms;
private Date modymdhms;
private final String pszqint = "102"; /* ... */ !
}!
§ Better?
class Customer {
private Date generationTimestamp; !
private Date modificationTimestamp; !
private final String recordId = "102"; /* ... */ !
}!
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10. More recommendations...
§ Class names
Customer, Account, AddressParser, ...
§ Method names
postPayment, deletePage, ....
§ When constructors are overloaded...
new Complex(23.0);!
Complex.fromRealNumber(23.0); !
§ Pick one word per concept
get, fetch, retrieve...
§ Don´t be cute. Jokes out of the code.
public void saveTheUniverse() {...}
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11. Bad Comments
§ Redundant, noise, irrelevant, obsolet, „funny“ comments
/**!
* Returns the day of the month. *!
* @return the day of the month. */!
public int getDayOfMonth() {!
return dayOfMonth;!
}!
!
/** Always return true. **/!
public boolean isAvailable() {!
!return false;!
}!
!
//Magic. Do not touch !
/* Added by Ana Cortés (4-4-2008) */!
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12. Bad Comments
/** !
* Dear maintainer:!
* !
* Once you are done trying to 'optimize' this routine,!
* and have realized what a terrible mistake that was,!
* please increment the following counter as a warning!
* to the next guy:!
* !
* total_hours_wasted_here = 42!
**/!
§ Commented-Out Code
InputStreamResponse response = new InputStreamResponse();!
response.setBody(formatter.getResultStream(), ft.getByteCount()); !
// InputStream resultsStream = formatter.getResultStream(); !
// StreamReader reader = new StreamReader(resultsStream); !
// response.setContent(reader.read(formatter.getByteCount())); !
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13. Good Comments
§ Legal comments
// Copyright (C) 2003 by Object Mentor, Inc. All rights reserved.
// Released under the terms of the GNU General Public License version 2 or later. !
§ Informative, clarification comments
// format matched kk:mm:ss EEE, MMM dd, yyyy !
Pattern timeMatcher = Pattern.compile("d*:d*:d* w*, w* d*, d*"); !
§ Amplification comments
String listItemContent = match.group(3).trim(); !
// the trim is real important. It removes the starting !
// spaces that could cause the item to be recognized
// as another list.
§ TODO comments
§ Javadocs in Public APIs
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14. Functions - Small!!
public static String testableHtml( PageData pageData,boolean
includeSuiteSetup) throws Exception {
WikiPage wikiPage = pageData.getWikiPage();!
StringBuffer buffer = new StringBuffer();!
if (pageData.hasAttribute("Test")) {!
if (includeSuiteSetup) {!
WikiPage suiteSetup =
PageCrawlerImpl.getInheritedPage( SuiteResponder. SETUP_NAME, wikiPage);
!
if (suiteSetup != null) {!
WikiPagePath pagePath =
suiteSetup.getPageCrawler().getFullPath(suiteSetup);!
String pagePathName = PathParser.render(pagePath); !
buffer.append("!include -
setup .").append(pagePathName).append("n");!
} !
}!
WikiPage setup = PageCrawlerImpl.getInheritedPage("SetUp",
wikiPage);!
... 40 lines more!
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15. Functions - Small!!
public static String renderPageWithSetupsAndTeardowns (PageData pageData,
boolean isSuite) throws Exception {
boolean isTestPage = pageData.hasAttribute("Test"); !
if (isTestPage) { !
WikiPage testPage = pageData.getWikiPage(); !
StringBuffer newPageContent = new StringBuffer(); !
includeSetupPages(testPage, newPageContent, isSuite); !
newPageContent.append(pageData.getContent()); !
includeTeardownPages(testPage, newPageContent, isSuite); !
pageData.setContent(newPageContent.toString()); !
} !
return pageData.getHtml(); !
}!
!
!
§ Better?
!
public static String renderPageWithSetupsAndTeardowns (PageData pageData,
boolean isSuite) throws Exception { !
if (isTestPage(pageData)) !
includeSetupAndTeardownPages(pageData, isSuite); !
return pageData.getHtml(); !
} !
!
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16. Command query separation
§ What does it mean?
public boolean set(String attribute, String value);!
!
if (set("username", "unclebob")) { ... } !
!
§ Better?
if (attributeExists("username")) { !
setAttribute("username", "unclebob"); !
} !
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17. Don´t return null
§ Throw exceptions or return special case object
!
List<Employee> employees = getEmployees(); !
if (employees != null) { !
for(Employee e : employees) { !
totalPay += e.getPay(); !
} !
} !
!
§ How to remove != null in the code?
public List<Employee> getEmployees() { !
if( .. there are no employees .. ) !
return Collections.emptyList(); !
} !
!
!
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18. Don´t return null
public void registerItem(Item item) { !
if (item != null) { !
ItemRegistry registry = persistentStore.getItemRegistry();!
if (registry != null) { !
Item existing = registry.getItem(item.getID());
if (existing.getBillingPeriod().hasRetailOwner()) { !
existing.register(item); !
} !
} !
} !
} !
!
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19. Have no side effects
§ Where is the side effect?
public boolean checkPassword(String userName, String password) { !
User user = UserGateway.findByName(userName);
if (user != User.NULL) { !
String codedPhrase = user.getPhraseEncodedByPassword(); !
String phrase = cryptographer.decrypt(codedPhrase, password);!
if ("Valid Password".equals(phrase)) { !
! Session.initialize(); !
return true; !
} !
} !
return false; !
} !
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20. Prefer exceptions to returning error codes
if (deletePage(page) == E_OK) {
if (registry.deleteReference(page.name) == E_OK) { !
if (configKeys.deleteKey(page.name.makeKey()) == E_OK{ !
logger.log("page deleted"); !
} else {
logger.log("configKey not deleted"); !
}
} else { !
logger.log("deleteReference from registry failed"); !
} !
} else {
logger.log("delete failed"); return E_ERROR; !
} !
!
!
public enum error {!
OK, INVALID, NO_SUCH, LOCKED, OUT_OF_RESOURCES;!
}!
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21. Prefer exceptions to returning error codes
§ Better?
public void delete(Page page) { !
try { !
!deletePageAndAllReferences(page); !
} !
catch (Exception e) {!
logError(e); !
} !
} !
!
private void deletePageAndAllReferences(Page page) throws Exception {
!
deletePage(page);
registry.deleteReference(page.getName()); !
configKeys.deleteKey(page.getKey()); !
}!
!
private void logError(Exception e) {!
logger.log(e.getMessage());!
}!05.02.2013 21 www.consol.com
!

22. Keeping tests clean
public void testGetPageHierarchyAsXml() throws Exception { !
crawler.addPage(root, PathParser.parse("PageOne")); !
crawler.addPage(root, PathParser.parse("PageOne.ChildOne"));
crawler.addPage(root, PathParser.parse("PageTwo")); !
request.setResource("root"); !
request.addInput("type", "pages");
Responder responder = new SerializedPageResponder(); !
SimpleResponse response = !
(SimpleResponse) responder.makeResponse( new
FitNesseContext(root), request); !
String xml = response.getContent(); !
assertEquals("text/xml", response.getContentType());
assertSubString("<name>PageOne</name>", xml);
assertSubString("<name>PageTwo</name>", xml);
assertSubString("<name>ChildOne</name>", xml); !
} !
!
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23. Keeping tests clean
§ Better?
!
public void testGetPageHierarchyAsXml() throws Exception { !
makePages("PageOne", "PageOne.ChildOne", "PageTwo");!
!
submitRequest("root", "type:pages"); !
!
assertResponseIsXML(); !
assertResponseContains( !
"<name>PageOne</name>", "<name>PageTwo</name>",
"<name>ChildOne</name>" ); !
} !
!
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24. Summary
§ Read „Clean Code“ book.
§ Be a little more careful with the code you write
§ Write with the „audience“ in mind
§ Follow the „Boy Scout Rule“
§ Leave the campground cleaner than you found it
§ Use tools that help you cleaning up
§ Write Clean Tests
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25. Thank you!
Danke!
Gracias!
!
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