changing the main class hardcoded values programatically with out extra file

[Ramya Chowdary]

Iam having only one main class and I've hardcoded the values like password in the main class file.Then we are giving the option of changing password for the user.

The obvious way is to change the value of password variable ,but it works for that instance of running program. There are ways like configuaration files,Serialization .But they create one more extra file. Is it possible to do with one and only one main class.

What should i do to reflect in every execution?

[Ulf Dittmer]

I'm not sure I understand exactly when the value needs to be changed, but can't you pass it in as a command-line parameter?

[Henry Wong]

Other options include....

- Having the program get the password from the command line
- Having the program get the password from an environment variable
- Having the program get it from the user (via prompt)


There is not magic here. If you don't want to store this password in the program, or in an external file, it has to be store somewhere else.

Henry

[Ramya Chowdary]

Iam not asking how to get the password from the user for comparison.I mean

If i store the password in the code,
like strPass="PASSWORD";

now i given option of changing the password like

strPass = "SomeOtherPassword";

Now you terminate the Program,you lost the changes you made because those are the memory values and you didn't dump them to your program.

[Ramya Chowdary]

something like

  
 
class Ex
{
     strPass="PasswordAsINTheFile";
 
     ChangePassword()
     {
         //ask the user for new password
         
          strPass = //Whatever user given;
      }
 
     public static void main(String a[])
     {
         //Get the password from the user 
         //Authenticate
          //YOU've given option of changing password
         
          //now User wants to change his password
          
         if(UserWantstoCHANGEPasswor)
                 ChangePassword();
 

 
       //some other stuff
       }
}
 

 

  

User changed the password and the program terminated,

You start the program again,the password again the original not the one user changed.

How we can solve this by not storing the password anywhere else other than the code it self?

[Ernest Friedman-Hill]

In theory, you could find the .class file and change the data in the class file itself. There are several different ways you might accomplish this, but all of them are pretty silly.

If you package your application in a jar file, then you might consider storing the data in a file in the jar file, and then having the program update the jar file. This is still silly, but maybe a little less so.

And of course, both of these schemes assume your .class or .jar file is writeable; what if it's stored on a CD?

[chandrakant karale]

QUOTE]Now you terminate the Program,you lost the changes you made because those are the memory values and you didn't dump them to your program.[

Once your program terminates and you want to retain value you have to persist it some where.

In theory, you could find the .class file and change the data in the class file itself

And modifying class file is surely not the best idea, plus the medium should be writable.

IMHO Creation of an extra file, using some existing file to store this change is the only elegant and standard way of doing this.

[Daniel Chemko]

1. Storing the password in the class isn't just dangerous, but stupidly dangerous. If you rely on the obscurity of burying the password into the class, you're just welcoming disaster. There are too many better places to store it that I almost wish to just leave this topic alone.

2. If you really must use this, the only sane solution is to use ASM (http://asm.objectweb.org/) to re-engineer the class to which will contain the new password (not even close to simple thats for sure) then use JRE 1.5+'s java.lang.instrument package to redefine the runtime instance of the class so that you know it worked. Once re-engineered and redefined successfully, you can then attempt to write the byte array over the original class file if you can find it. Hint: start with MyReallyBadIdea.class.getClassLoader().getResource(MyReallyBadIdea.class.getName().replace(".", "/") + ".class").

3. Finally, this is the worst solution to any problem you could possibly have and you're in for a world of hurt trying, even if its just for fun.

[Ramya Chowdary]

I've taken password as an example for changing code...it may look stupid .

I've seen win32 applications like this which doesn't store passwords anywhere ( Registry,property pages,configuration files....etc).I think its possible because a win32 valid executable can contain resource files.

At machine level , a program is combination of code i.e instructions and DATA,so can't we change the data i.e state of the program

Reverse Engineering the class file and changing resources like text strings are certainly possible.But,what i am looking is programatical change....

Anyway thanks for your suggestions....
[ March 01, 2008: Message edited by: ramya sri ]