Class.forName("org.gjt.mm.mysql.Driver");注册驱动

学校时，照抄老师的代码。工作时，直接调用成熟框架的方法。从没有真正自己研究下。(惭愧)
今天试着自己写写JDBC连接数据库。
看到代码
……
Class.forName("org.gjt.mm.mysql.Driver");
conn = DriverManager.getConnection(url,username,password);
……
我在想孤零零的一句【Class.forName("org.gjt.mm.mysql.Driver");】到底做了什么，网友说：注册MySql驱动。可是自己习惯思维是，看到调用。这连引用都没有。它加载了谁，又调用了谁呢？
想不出来！“何不看看驱动源码”呢？对啊！理解解压【org.gjt.mm.mysql.Driver】
org\gjt\mm\mysql文件夹下就一个文件：类Driver

package org.gjt.mm.mysql;

import java.sql.SQLException;

public class Driver extends com.mysql.jdbc.Driver
{
}

package org.gjt.mm.mysql;

import java.sql.SQLException;

public class Driver extends com.mysql.jdbc.Driver
{
}

再去看看 com.mysql.jdbc.Driver

package com.mysql.jdbc;

import java.sql.DriverManager;
import java.sql.SQLException;

public class Driver extends NonRegisteringDriver
  implements java.sql.Driver
{
  static
  {
    try
    {
      DriverManager.registerDriver(new Driver());
    } catch (SQLException E) {
      throw new RuntimeException("Can't register driver!");
    }
  }
}

package com.mysql.jdbc;

import java.sql.DriverManager;
import java.sql.SQLException;

public class Driver extends NonRegisteringDriver
  implements java.sql.Driver
{
  static
  {
    try
    {
      DriverManager.registerDriver(new Driver());
    } catch (SQLException E) {
      throw new RuntimeException("Can't register driver!");
    }
  }
}

兜兜转转，最后调用的还是【DriverManager.registerDriver(new Driver());】
但源文件里的

   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();

// Not Required -- drivers.addElement(di);

writeDrivers.addElement(di);
println("registerDriver: " + di);

/* update the read copy of drivers vector */
readDrivers = (java.util.Vector) writeDrivers.clone();

   }