How I can logout from Facebook in my custom android app?

I am building an android application where I am using facebook login and after facebook login I get access_token and session that are stored in shared preferences in private mode.

I am using the below facebook login code in an activity and i want the user to logout from facebook from another fragment. How do i code on the fragment so that my current logged-in account logs out from facebook.

Here is my facebook login code -

/**
 * Function to login into facebook
 */
@SuppressWarnings("deprecation")
public void loginToFacebook() {

    mPrefs = getPreferences(MODE_PRIVATE);
    String access_token = mPrefs.getString("access_token", null);
    long expires = mPrefs.getLong("access_expires", 0);

    if (access_token != null) {
        facebook.setAccessToken(access_token);
        // call getprofileinformation function to get user details
        getProfileInformation();

        Log.d("FB Sessions", "" + facebook.isSessionValid());
    }

    if (expires != 0) {
        facebook.setAccessExpires(expires);
    }

    if (!facebook.isSessionValid()) {
        facebook.authorize(this,
                new String[]{"email", "publish_stream"},
                new Facebook.DialogListener() {

                    @Override
                    public void onCancel() {
                        // Function to handle cancel event
                    }

                    @Override
                    public void onComplete(Bundle values) {
                        // Function to handle complete event
                        // Edit Preferences and update facebook acess_token
                        SharedPreferences.Editor editor = mPrefs.edit();
                        editor.putString("access_token",
                                facebook.getAccessToken());
                        editor.putLong("access_expires",
                                facebook.getAccessExpires());
                        editor.commit();

                        // call getprofileinformation function to get user
                        // details
                        getProfileInformation();

                    }

                    @Override
                    public void onError(DialogError error) {
                        // Function to handle error

                    }

                    @Override
                    public void onFacebookError(FacebookError fberror) {
                        // Function to handle Facebook errors

                    }

                });
    }
}

Help is appreciated, thanks!