private static void findResources(Set<String> set, File file, String dirName,
			String extension) {

		if (!file.exists()) {
			return;
		}

		String[] names = file.list();
		if (names == null) {
			return;
		}

		for (String element : names) {
			if (extension == null || element.endsWith(extension)) {
				set.add(dirName + "/" + element);
			}
		}
	}
Search the directory for files ending in the given extension and add them to the list 
that is returned

@param set the set to which resource names will be added
@param file directory, e.g., "resources/defaultTools"
@param dirName name of sub-directory, e.g. "defaultTools"
@param extension file extension to look for
Ghidra/Framework/Gui/src/main/java/resources/ResourceManager.java