Java Cookbook

Precompiling the RE

Problem

You need to use the same RE many times over.

Solution

Precompile it using class recompile and include the resulting code fragment into your Java source code.

Discussion

Some REs never change. Those that don’t can be precompiled to speed up your program’s initialization. The class recompile (the only class in this API whose name doesn’t fit the Java capitalization style rules) contains a main program that requires two arguments: a Java identifier prefix and an RE pattern. When running it, remember that you should quote the RE pattern, as many of the special characters are the same for the REs as they are for many command-line interpreters. You run it by giving the java command, the full class name, the identifier prefix, and the RE pattern as one command line. Once you’ve seen that the RE is correct, you can run the command again, redirecting the results into a new Java file. You can then edit this file into a complete program or copy it into an existing Java file.

> java org.apache.regexp.recompile Name "[A-Z][a-z]+" // Pre-compiled regular expression '[A-Z][a-z]+' private static char[] NamePatternInstructions = { 0x007c, 0x0000, 0x0019, 0x005b, 0x0001, 0x0005, 0x0041, 0x005a, 0x005b, 0x0001, 0x0005, 0x0061, 0x007a, 0x007c, 0x0000, 0x0006, 0x0047, 0x0000, 0xfff8, 0x007c, 0x0000, 0x0003, 0x004e, 0x0000, 0x0003, 0x0045, 0x0000, 0x0000, }; private static RE NamePattern = new RE(new REProgram(NamePatternInstructions)); > java org.apache.regexp.recompile Name ...