Review

class CompileTask {
  public void execute() {
    if (this.outputFile == null) {
      throw new BuildException("outputFile attribute must be set");
    }

    Compiler.setLoggingLevel(Level.OFF);

    CompilerOptions options = createCompilerOptions();
    Compiler compiler = createCompiler(options);

    JSSourceFile[] externs = findExternFiles();
    JSSourceFile[] sources = findSourceFiles();

    if (isStale()) {
      log("Compiling " + sources.length + " file(s) with " +
          externs.length + " extern(s)");

      Result result = compiler.compile(externs, sources, options);
      if (result.success) {
        writeResult(compiler.toSource());
      } else {
        throw new BuildException("Compilation failed.");
      }
    } else {
      log("None of the files changed. Compilation skipped.");
    }
  }

}