Registering class - what does it mean?

Question

In one book dealing with JDBC there's statement like: "Whenever a driver is loaded into memory
Class.forName("org.gjt.mm.mysql.Driver")
it is registered as an available driver with the
java.sql.DriverManager
class".
I have to say that I'm not newbie in database/JDBC programming and that I already created dozens of programs and web applications working with databases using DriverManager/DataSource approaches but now I'd like to understand what's really going on in the background with driver class.
When you say "driver is registered" what does it really mean; what is registered and where?, how it is registered?, is it registered somewhere as ActiveX/COM component in Windows registry?

Answer 1

hi sbrbot,
There has been lot of confusion in people who try to get deep into what the books are telling. let me tell you what i could understand from analysing the informations and specifications ....
when u call Class.forName with the driver class as the argument.., u instantiate a class of the driver.. like org.gjit.mm.mysql.Driver.. This class will contain some mechanism.., usually a static method that will call the java.sql.DriverManager.registerDriver(DriverClass) method.. this method needs the driver class as argument.. u can see it in the java sdk source code..
The DriverManager now gets a handle to the driver class instance and whatit does can be seen from the foll. code ..in the java.sql.DriverManager class...
    public static synchronized void registerDriver(java.sql.Driver driver)
     throws SQLException {
     if (!initialized) {
         initialize();
     DriverInfo di = new DriverInfo();
     di.driver = driver;
     di.driverClass = driver.getClass();
     di.driverClassName = di.driverClass.getName();
     drivers.addElement(di);
     println("registerDriver: " + di);
    }for your information.. if u are again doubtful abt something.. see the foll. code part tooo again from java.sql.DriverManager
// DriverInfo is a package-private support class.
class DriverInfo {
    Driver         driver;
    Class          driverClass;
    String         driverClassName;
    public String toString() {
     return ("driver[className=" + driverClassName + "," + driver + "]");
    }So i hope u now know how the DriverManager class stores the information about the drivers that are available.. :-D
Hope that was of some help.. do correct me if my concepts are wrong.
cheers,
-Jer