Facebook SDK for android - getting access token by passing username and password

Is there a way to get access token by passing the username and password with a method (Not to use the authorize method of the SDK)??

I want to have something like this:

private String GetFacebookAccessToken(String username , String password ){
 ...
}

In my app I want to have 2 facebook accounts , I want each time to login with a different account , I have the username & password saved.

Please help...