static void renameMainJava(File srcDir, S progID) {
  File fMain = new File(srcDir, "main.java");
  S src = loadTextFile(fMain);
  if (tok_classHasModifier(findMainClass(javaTok(src)), "public")) ret;
  S dummyClassName = dummyMainClassName(progID);
  src += "\nclass " + dummyClassName + "{}";
  saveTextFile(new File(srcDir, dummyClassName + ".java"), src);
  fMain.delete();
}