Java Performance Tuning

Better Optimizing Compilers

Look out for Java code compilers that specifically target performance optimizations. These are increasingly available. (I suggest searching the Web for java+compile+optimi and checking in Java magazines. A list is also included in Chapter 15.) Of course, all compilers try to optimize code, but some are better than others. Some companies put a great deal of effort into making their compiler produce the tightest, fastest code, while others tend to be distracted by other aspects of the Java environment and put less effort into the compile phase.

There are also some experimental compilers around. For example, the JAVAR compiler (http://www.extreme.indiana.edu/hpjava/) is a prototype compiler that automatically parallelizes parts of a Java application to improve performance.

It is possible to write preprocessors to automatically achieve many of the optimizations you can get with optimizing compilers; indeed, you can think of an optimizing compiler as a preprocessor together with a basic compiler (though in many cases it is better described as a postprocessor and recompiler). However, writing such a preprocessor is a significant task. Even if you ignore the Java code parsing or bytecode parsing required,^[18] any one preprocessor optimization can take months to create and verify. To get close to the full set of optimizations listed in the following sections could take years of development. Fortunately, it is not necessary for you to make that effort, because ...