What will be the output of the program?

class Happy extends Thread
{
final StringBuffer sb1 = new StringBuffer();
final StringBuffer sb2 = new StringBuffer();
public static void main(String args[])
{
final Happy h = new Happy();
new Thread()
{
public void run()
{
synchronized(this)
{
h.sb1.append("A");
h.sb2.append("B");
System.out.println(h.sb1);
System.out.println(h.sb2);
}
}
}.start();
new Thread()
{
public void run()
{
synchronized(this)
{
h.sb1.append("D");
h.sb2.append("C");
System.out.println(h.sb2);
System.out.println(h.sb1);
}
}
}.start();
}
}