Performance Optimization in Java

• Use byte instead of int for Percent
• Declare constants in interfaces instead of declaring static final members in class
• Use custom date class/long for Date/Calendar
• Use string.intern() to cache strings
• Use bitset instead of boolean arrays. use custom class for ObjectStatus
• Implement parent, child relationship in objects
• String comparison
  

string1 == string2 before comparing string1.length() == string2.length() && string1.equals(string2)

• Use StringBuffer for string concatnation

• reduce conversion between strings and numbers/ maintain a hashmap of strings to numbers for commonly used numbers lets say 1 to 100
  
• use caching for web services - EhCache with configurable session timeout
  
• use caching for transformed objects - EhCache with configurable session timeout
  

• Session Serialization
• do not keep clob's, blob's in serialized objects
• use wrappers around such objects / implement inheritance to move clobs to derived classes
• original values, which wont change during session - should be trimmed only to hold necessary information
  

• use multiple session attributes for storing objects in session
• create context object to pull values from session in a filter
• and use the context object at later stages instead of session
• at the end of response, in the filter update session attributes - depending on the dirty objects
• use obfuscator, compiler options to reduce code size
• http://www.j2ee.me/docs/books/performance/1st_edition/html/JPTOC.fm.html
• http://www.swtech.com/java/optimize/
• Timer - http://www.glenmccl.com/jperf/#Sample1
• http://www.javaperformancetuning.com/tips/rawtips.shtml