Prevent Ant from performing a task if a file is older than another file

how can I pre开发者_StackOverflow中文版vent Ant from processing a task if a source file is older than the current target. For example, I created a javacc file MyParser.jj and there is no need for javacc to re-generate the file MyParser.java as long as the MyParser.jj is older than MyParser.java.

As Aaron said, the javacc task shouldn't be executed on code that hasn't changed.

But, to answer to original question - there's an uptodate task that can be used for this purpose. Here's an example.

There must be a bug elsewhere or your version of Ant is too old. From the docs:

This task only invokes JavaCC if the grammar file is newer than the generated Java files.