public boolean add(SpdData data) {
        if (data == null)
            return false;
        if (data instanceof SpdStat) {
            return super.add(data);
        } else {
            return false;
        }
    }
public boolean add ( SpdData data ) { if ( data == null ) return false ; if ( data instanceof SpdStat ) { return super . add ( data ) ; } else { return false ; } }
Check data type and call super.add to add data - synchronized in super