【求助】学完线程，写了个死锁的线程，但老报错，为什么？

public class Test5 implements Runnable {

int flag;
static Object o1,o2 = new Object();

public void run() {

if(flag==1){
synchronized (o1) {
System.out.println("拿到o1");
synchronized (o2) {
System.out.println("也拿到o2");
}
}
}

if(flag==2){
synchronized (o2) {
System.out.println("拿到o2");
synchronized (o1) {
System.out.println("也拿到o1");
}
}
}

}

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Test5 t1 = new Test5();
t1.flag = 1;
Test5 t2 = new Test5();
t2.flag = 2;
Thread r1 = new Thread(t1);
Thread r2 = new Thread(t2);

r1.start();
r2.start();

}

}