java multithread

Hi,
Thanks for your multithreading java code. It helped me a lot.
But i have one issue. My code is look like this.

public class classname extends Thread {

public classname() {
super();
/**Here creating objects for other classes and calling those methods
classC ob3=new classC();
classD ob4=new classD();
**/
start();
}

public void run() {
while (true) {

/** code something like this**/
classA ob1=new classA();
classB ob2=new classB();

try {

//900000 milliseconds equals to 15 minutes
Thread.sleep(900000);
} catch (Exception e) {
System.out.println(e);
}
}

}
}

I want two objects i.e ob1 and ob2 as two diferent threads and should run simultaneously without affecting each other.

Could you please help me out.
Thank you