java - How does Class.forName() work?

Question

I just learned about java.sql package. It uses Class.forName() to dynamically load the driver which extends DriverManager. Then we get connection using DriverManager.getConnection() method.

So how does the entire thing work?
How does DriverManager class know how to get the connection without using class name of the actual driver.

Also can we use Class.forName() for custom applications... if this is explained with an example I will be very happy.

Answer 1

Class.forName simply loads a class, including running its static initializers, like this:

class Foo {
    static {
        System.out.println("Foo initializing");
    }
}

public class Test {
    public static void main(String [] args) throws Exception {
        Class.forName("Foo");
    }
}

All the rest of the procedure you're talking about is JDBC-specific. The driver - which implements Driver, it doesn't extend DriverManager - simply registers an appropriate instance using DriverManager.registerDriver. Then when DriverManager needs to find a driver for a particular connection string, it calls connect on each registered driver in turn until one succeeds and returns a non-null connection.

Note that this way of registering drivers is reasonably old-fashioned - look at the docs for DriverManager for more modern ways of getting at a data source.