execute file from defined directory with Runtime.getRuntime().exec

I just want to execute my file from a specific folder. in my case /data/data/my-package/files/. So i tried :

 Process process2=Runtime.getRuntime().exec("cd /data/data/my-package/files/");
 process2.waitFor();
 process2=Runtime.getRuntime().exec("./myfile");

It doesn't work. could anyone tell me please the right way to do that . Thanks