初学问题：连接oracle数据库时，报错！！

try {
DBDriver = "oracle.jdbc.driver.OracleDriver";
ConnStr = "jdbc:oracle:thin:@delphi";
Class.forName(DBDriver);
Connection conn = DriverManager.getConnection(ConnStr, LoginName, Passwd);
stmt = conn.createStatement();
}
catch(ClassNotFoundException e) {
System.out.println("mydb(): " + e.getMessage());
}
我的代码执行到Class.forName(DBDriver);时抛出异常，好像时找不到类
oracle.jdbc.driver.OracleDriver，这是为什么阿！？？？