JavaAntiPatterns

Collection of bad coding practices

Posts Tagged ‘performance

Unneccessary thread safety of StringBuffer

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Use StringBuilder rather then StringBuffer, unless synchronization is required. StringBuilder is not thread safe, and therefore avoids the synchronization overhead of StringBuffer.

(submitted by Robert J. Walker)

Written by Alex

August 22, 2008 at 4:07 am

Posted in Strings, Threads

Tagged with , ,

LinkedLists as arrays

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java.util.LinkedList is a special type of collection designed for sequential access (stacks and queues). Being used as a random-accesed array, it is much slower than other List implementations. For instance, getting an item by index (get(n)) has constant complexity O(1) for ArrayLists, while for LinkedList, the complexity of that operation is O(n).

Use ArrayList (or Vector if synchronization is required) for random-accessed lists.

Written by Alex

November 22, 2007 at 1:03 pm

Posted in Collections

Tagged with , ,

Using URLs in Collections

with one comment

java.net.URL objects used as Map keys or Set items can result in a big performance issue. Internal implementation of equals() and hashCode() methods of java.net.URL class performs domain name resolution, so the time of their execution relies on an internet connection speed. If a computer is off-line, the time is nearly equal to a connection timeout (tens of seconds).

The same problem arises every time when URLs equality checking or hash code computation is performed.

Do not use java.net.URL to keep URL values. Use java.net.URI objects or the simple Strings instead.

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Written by Alex

November 22, 2007 at 12:25 pm

Posted in Collections

Tagged with , , , , , ,

Accessing the Map values using keySet iterator

with 13 comments

A common mistake is to retrieve values from a Map while iterating over the Map keys with keySet(). Calling Map.get(key) for each entry is expensive and should be avoided for better performance.

Use entrySet() iterator to avoid the Map.get(key) lookup.

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Written by Alex

November 22, 2007 at 12:02 pm

Posted in Collections

Tagged with , , ,