int numero;
cout<<"Ingrese numero"<<endl;
cin>>numero;

<form action="/registrardatos.php" method="post"> 
Seleccione una fruta o verdura: 
<select name="articulo"> 
<optgroup label="Frutas"> 
<option value="1">Naranjas</option> 
<option value="2">Manzanas</option> 
</optgroup> 
<optgroup label="Verduras"> 
<option value="3">Lechuga</option> 
<option value="4">Papas</option> 
</optgroup> 
</select> 
<br> 
<input type="submit" value="Enviar"> 
</form>

Statement stmt = con.createStatement();
ResultSet rs=stmt.executeQuery("SELECT * FROM tren");
System.out.println("Login\tPassword");
while(rs.next()) {
System.out.println(rs.getString("idTren")+"\t"+rs.getString("modelo"));
}

DriverManager.getConnection(
            					"jdbc:mysql://localhost/nombre_bd".....