Good Java Programming Practices

1. Lightning Talk on Java
Common Programming
Oversights
Chetan Narsude
January 20th, 2014

2. Don’t Swallow Exceptions
• Mistake
try {
}
catch (Exception e) {
e.printStackTrace();
}
• Bad
try {
}
catch (Exception e) {
logger.warn(“Exception”, e);
}
Recommended
try {
}
catch (Throwable e) {
if (e instanceof Error) {
throw (Error)e;
}
if (e instanceof RuntimeException) {
throw (Runtime)e;
}
• Ugly
try {
}
catch (Exception e) {
handleException(e);
}
/* somewhere else */
public void handleException(Exception e){}
throw new RuntimeException(e);
}

3. Don’t wrap Throwable in
RuntimeException
try {
try {
…
…
}
}
catch (Throwable cause) {
catch (Throwable cause) {
throw new RuntimeException(cause);
}
DTThrowable.rethrow(cause);
}

4. Don’t Catch All Throwable
try {
try {
…
…
}
}
catch (Throwable cause) {
catch (Error error) {
throw new RuntimeException(cause);
}
throw error;
}
catch (RuntimeException runtime) {
throw runtime;
}
catch (Throwable cause) {
throw new Runtime(cause);
}

5. Don’t Use Static Instance of
SimpleDateFormat
private static final DateFormat dateFormat
= new SimpleDateFormat("yyyy-MM-dd");
…
/* somewhere in the code */
ed =
dateFormat.parse(dateInput.readUTF());
…
/* somewhere in the code */
ed = new SimpleDateFormat("yyyy-MMdd").parse(dateInput.readUTF());
private static final ThreadLocal<DateFormat> dateFormat = new ThreadLocal<DateFormat>()
{
@Override
protected DateFormat initialValue()
{
return new SimpleDateFormat(“yyyy-MM-dd”);
}
}
…
/* somewhere in the code */
ed = dateFormat.get().parse(dateInput.readUTF());

6. Synchronize Only on Final
private Object mutex = new Object();
private final Object mutex = new Object();
/* somewhere in the code */
synchronized (mutex) {
reload = true;
mutex.notify();
}
/* somewhere in the code */
synchronized (mutex) {
reload = true;
mutex.notify();
}
/* possibly elsewhere in the code */
public void setMutex(Object mutex)
{
this.mutex = mutex;
}

7. Avoid Concatenation While Logging
/* various ways of wrongly using logger */
logger.debug(“Exception = “ + e.getMessage());
logger.debug(“Exception = {}”, e);
logger.debug(“Exception “ + id + “ “ + e.toString());
/* just print the message from exception */
logger.debug(“Exception = {}“, e.getMessage());
/* print the exception stack trace */
logger.debug(“Some Operation”, e);
/* print templatized message with exception stack trace */
logger.debug(“Exception {}“, id, e);

8. Prevent Resource Leak
InputStream stream = new …Stream();
InputStream stream = new …Stream();
while (…) {
try {
process(stream);
while (…) {
}
process(stream);
stream.close();
}
}
finally {
stream.close();
}