startActivityForResult (FragmentA <-> FragmentB)

FragmentA.java

// FragmentA (in Activity A)
private void showActivityB(int requestCode) {
    Intent intent = new Intent(getActivity(), ActivityB.class);
    startActivityForResult(intent, requestCode);
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode != Activity.RESULT_OK) {
        return;
    }

    String val = data.getStringExtra("key1");
}

FragmentB.java

// FragmentB (in ActivityB)
private void close() {
    Intent intent = new Intent();
    intent.putExtra("key1", "val1");
    getActivity().setResult(Activity.RESULT_OK, intent);
}