Performance Management Guide

Java Performance Guidelines

The following are basic Java performance issues:

• Use StringBuffer instead of string concatenations, when doing excessive string manipulations to avoid unnecessarily creating objects that eventually must undergo garbage collection.
• Avoid excessive writing to the Java console to reduce the cost of string manipulations, text formatting, and output.
• Avoid the costs of object creation and manipulation by using primitive types for variables when necessary.
• Cache frequently used objects to reduce the amount of garbage collection needed, and avoid the need to repeatedly create the objects.
• Group native operations to reduce the number of Java Native Interface (JNI) calls when possible.
• Use synchronized methods only when necessary, to limit the multitasking in the JVM and operating system.
• Avoid invoking the garbage collector unless necessary. If you must invoke it, do so only during idle time or some noncritical phase.
• Use int instead of long whenever possible, because 32-bit operations are executed faster than 64-bit.
• Declare methods as final whenever possible. Final methods are handled better by the JVM.
• Use the key word static final when creating constants in order to reduce the number of times the variables need to be initialized.
• Avoid unnecessary "casts" and "instanceof" references because casting in Java is not done at compile time but at run time.
• Avoid the use of vectors whenever possible when an array will suffice.
• Add and delete items from the end of the vector for better performance.
• Compile Java files with the -O option.
• Avoid allocating objects within loops.
• Use buffer I/O and tune the buffer size.
• Use connection pools and cached-prepared statements for database access.
• Use connection pools to the database and reuse connections rather than repeatedly opening and closing connections.
• Maximize thread lifetimes and minimize thread creation and destruction cycles.
• Minimize contention for shared resources.
• Minimize creation of short lived objects.
• Avoid remote method calls.
• Use callbacks to avoid blocking remote method calls.
• Avoid creating an object that would only be used for accessing a method.
• Whenever possible, keep synchronized methods out of loops.
• Store string and char data as Unicode in the database.
• Reorder CLASSPATH so that the most used libraries occur first.