Add or subtract the time difference between two dates in java

I need to add or subtract the time difference between dates, If the ESTADOLINEA is 1 add, and if the ESTADOLINEA is 2, subtract the time.

This is the SQL table:

My idea is to loop through the records

This is my code:

private void fisico(ResultSet rs) {
    try {
        while (rs.next()) {
            if (rs.getRow() != 0) {
                //si es 2 la maquina esta parada, si NO la maquina esta MARCHA 
                if (rs.getInt(2) == 2) {
                    System.out.println(rs.getInt(1) + " Maquina parada " + rs.getInt(2));
                    fechaInicio = String.valueOf(rs.getTimestamp(4));
                } else {
                    System.out.println(rs.getInt(1) + " Maquina en marcha " + rs.getInt(2));
                }
            } else {
            }
        }
    } catch (SQLException ex) {
        System.err.println("" + ex);
    }
}