假设如下代码中，若t1线程在t2线程启动之前已经完成启动。代码的输出是（）...
public static void main(String[]args)throws Exception {
final Object obj = new Object()
Thread t1 = new Thread() {
public void run() {
synchronized (obj) {
try {
obj.wait()
System.out.println("Thread 1 wake up.")
} catch (InterruptedException e) {
}
}
}
}
t1.start()
Thread.sleep(1000)//We assume thread 1 must start up within 1 sec.
Thread t2 = new Thread() {
public void run() {
synchronized (obj) {
obj.notifyAll()
System.out.println("Thread 2 sent notify.")
}
}
}
t2.start()
}
