Java Performance Tuning

Replacing JDK Classes

It is possible for you to replace JDK classes directly. Unfortunately, you can’t distribute these altered classes with any application or applet unless you have complete control of the target environment. Although you often do have this control with in-house and enterprise-developed applications, most enterprises prefer not to deploy alterations to externally built classes. The alterations then would not be supported by the vendor (Sun in this case) and may violate the license, so contact the vendor if you need to do this. In addition, altering classes in this way can be a significant maintenance problem.^[16]

The upshot is that you can easily alter JDK-supplied classes for development purposes, which can be useful for various reasons including debugging and tuning. But if you need the functionality in your deployed application, you need to provide classes that are used instead of the JDK classes by redirecting method calls into your own classes.

Replacing JDK classes indirectly in this way is a valid tuning technique. Some JDK classes, such as StreamTokenizer (see Section 5.4), are inefficient and can be replaced quite easily since you normally use them in small, well-defined parts of a program. Other JDK classes, like Date , BigDecimal , and String are used all over the place, and it can take a large effort to replace references with your own versions of these classes. The best way to replace these classes is to start from the design stage, so that you ...