1. Java anti-patterns:
Dark knight rises.
Сергей Моренец
28 февраля 2013 г.

2. Agenda
• Design patterns
• Anti-patterns overview
• Q&A

4. Design patterns
• Design Patterns: Elements of Reusable Object-Oriented
Software
• Published on October 21, 1994
• Authors are Erich Gamma, Richard Helm, Ralph
Johnson and John Vlissides, referred as Gang of Four
• Creational, structural and behavioral patterns.

5. Hero of the day

6. Java Anti-docs
/**
* Rejects current task
*/
public void approve() {
…
}

7. Inline conversion
int recordId = -1;
try {
recordId = Integer.parseInt(columnRecordId);
} catch (NumberFormatException e) {
recordId = 0;
}

8. Exception handler
avoidance
ValidationResultCollector vrc = collector.validate();
if(vrc.hasError()) {
ValidationResult result = vrc.getError();
errorText = result.getErrorText();
} else if(vrc.getErrorCode() == CPFErrorID.getNoCPFError()) {
}

9. Disuse of helper
libraries
if (param.getFileName() != null &&
param.getFileName().length() > 4) {
try {
if (param.getFileName().contains(".")) {
name = param.getFileName().substring(0,
param.getFileName().lastIndexOf("."));
} else name = attach.getFileName();
} catch (Exception e) {
e.printStackTrace();
String errorMessage = e.getMessage();
}
}

10. Disuse of helper
libraries
String name = FilenameUtils.getBaseName(
parameter.getFileName());
String extension = FilenameUtils.getExtension(
parameter.getFileName());

11. Misuse of inheritance
• public class SuperMap<K, V> extends
HashMap<K,V>{
• @Override
• public V get(Object key) {
• …
• }
• }

12. Upcasting
public abstract class BaseClass {
public void do() {
((DerivedClass) this).validate();
}
}
class DerivedClass extends BaseClass {
public void validate() {
}
}

13. Lack of synchronization
public class ScreenManager {
private static ScreenManager instance;
public static ScreenManager getInstance() {
if (instance == null) {
instance = new ScreenManager();
}
return instance;
}
}

14. State inconsistency
public class AccountManager {
private boolean inProgress = false;
public void submit() {
if (inProgress) {
return;
}
inProgress = true;
…
inProgress = false;
}
}

15. State inconsistency
public class AccountManager {
private final Lock lock = new ReentrantLock();
public void submit() {
lock.lock();
…
lock.unlock();
}
}

16. State inconsistency
public class AccountManager {
private final Lock lock = new ReentrantLock();
public void submit() {
try {
lock.lock();
…
} finally {
lock.unlock();
}
}
}

17. Platform-dependent API
File tmp = new File("C:Temp1.tmp");
File exp = new File("export-2013-02-01T12:30.txt");
File f = new File(path +'/'+ filename);

18. Platform-dependent API
File tmp = File.createTempFile("myapp","tmp");
File exp = new File("export-2013-02-01_1230.txt");
File f = new File(path +File. pathSeparator+ filename);
File dir = new File(path);
File f = new File(dir, filename);

19. Infinitive heap
byte[] pdf = toPdf(file);

20. Infinitive heap
File pdf = new File(file);
InputStream in = new FileInputStream(pdf);

21. Unbuffered streams
InputStream in = new FileInputStream(file);
int b;
while ((b = in.read()) != -1) {
...
}

22. Unbuffered streams
InputStream in = new BufferedInputStream(new
FileInputStream(file))

23. Wrong propagation
try {
…
} catch(ParseException e) {
LOGGER.error(e.getMessage());
throw new RuntimeException();
throw new RuntimeException(e.toString());
throw new RuntimeException(e.getMessage());
throw new RuntimeException(e);
}

24. Wrong propagation
try {
} catch(ParseException e) {
throw new RuntimeException(e.getMessage(), e);
}

25. Impossible exception
try {
... do risky stuff ...
} catch(SomeException e) {
// never happens
}

26. Impossible exception
try {
... do risky stuff ...
} catch(SomeException e) {
// never happens hopefully
throw new IllegalStateException(e.getMessage(), e);
}

27. Unnecessary Calendar
Calendar cal = new
GregorianCalender(TimeZone.getTimeZone("Europe/Kyiv"));
cal.setTime(date);
cal.add(Calendar.HOUR_OF_DAY, 8);
date = cal.getTime();

28. Unnecessary Calendar
date = new Date(date.getTime() + 8L * 3600L * 1000L);

29. Misleading calendar
Calendar c = Calendar.getInstance();
c.set(2009, Calendar.JANUARY, 15);
c.getTime() - ?

30. Misleading calendar
Calendar c = new GregorianCalendar(timeZone);
c.set(2009, Calendar.JANUARY, 15);

31. Global constants
public interface Constants {
String version = "1.0";
String dateFormat = "dd.MM.yyyy";
String configFile = ".apprc";
int maxNameLength = 32;
String someQuery = "SELECT * FROM ...";
}

32. Static initializers
class Cache {
private static final Timer timer = new Timer();
}

33. Static initializers
class Cache {
private static Timer timer;
public static startTimer() {
timer = new Timer();
}
}

34. Reflection overuse
Class beanClass = ...
if (beanClass.newInstance() instanceof TestBean) ...

35. Reflection overuse
Class beanClass = ...
if (TestBean.class.isAssignableFrom(beanClass)) ...

36. Map iteration
Map<String, String> map = …;
for (String key : map.keySet()) {
String value = map.get(key);
…
}

37. Map iteration
Map<String, String> map = …;
for (Entry<String, String> entry : map.entrySet()) {
String key = entry.getKey();
String value = entry.getValue();
…
}

38. Time measurement
long startTime = System.currentTimeMillis();
...
long elapsedTime = System.currentTimeMillis() -
startTime;

39. Time measurement
long startTime = System.nanoTime();
...
long elapsedTime = (System.nanoTime() - startTime) /
1000000;

40. Q&A
• Сергей Моренец, morenets@mail.ru

41. Collection<User> users = ...
if (users != null && !users.isEmpty()) {
int i = 0;
for (User user : user) {
if (i > 0)
break;
output.setUserId(user.getId());
i++;
}}