If you are looking to know, How to override home button programmatically in android, then below I have provided the simple solution.
You have to do just a simple thing i.e to override the onKeyDown function in your application, given is the code snippet that opens a dialog box on clicking home button:-

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if ((keyCode == KeyEvent.KEYCODE_HOME)) {
            showCustomDialog("This is just an example to open a dialog when you press home button, you can do other thing also");
            return true;
        }
        return false;
    }

void showCustomDialog(String msg)
{
   AlertDialog.Builder alertDialog;
   alertDialog= new AlertDialog.Builder(activity.this);
   alertDialog.setTitle("");
   alertDialog.setMessage(msg);
   alertDialog.setPositiveButton("OK",new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog,int which) 
                   {
                    dialog.cancel();
          }
        });
   alertDialog.show();
  }