From what time I've spent with threads in Java, I've found these two ways to write threads.

public class ThreadA implements Runnable {
    public void run() {
    	//Code
    }
}
//with a "new Thread(threadA).start()" call


public class ThreadB extends Thread {
    public ThreadB() {
    	super("ThreadB");
    }
    public void run() {
    	//Code
    }
}
//with a "threadB.start()" call

Is there any significant difference in these two blocks of code?