JD-GUI

//source
public static void main(String... args) {
    String str = "";
    for(int i = 0;i < 100; i++) {
        str += "hoge";
    }
}


//decompile
public static void main(String[] args)
  {
    String str = "";
    for (int i = 0; i < 100; i++)
      str = str + "hoge";
  }