In JDK 1.5-, you have only an undocumented and hence deprecated technique of invoking the javac.exe compiler programmatically.

You normally invoke javac.exe from the command line, but you can also invoke it from within a Java program. Use the sun.tools.javac.Main class located in jdk1.6.0_06/lib/tools.jar to pass it an array of Strings equivalent to the command line parameters. You might do this to bulk-compile large numbers of files without reloading the javac compiler for each file. Here is how you use it:

You too might use this technique for speed to avoid reloading javac.exe, or to have arbitrarily long command lines. You can also get long command lines with the @listOfFiles technique.

Capturing the error messages from javac.exe can be a hassle since they scroll off the screen faster than you can read them. Ordinary > redirection won’t capture them to a file because they are going to STDERR, not STDOUT. I use a program called 4NT to solve this problem. It lets you independently redirect STDOUT and STDERR. You can also use the -Xstdout to bypass the problem.

In Java 1.6+ programmatic invocation of the compiler will become an official interface. Read the JSR. For more details on how you do on the fly composing, compilation and execution see my sample code.