static Object obj = new Object(),静态对象和非静态对象有什么区别

下面这段程序中，Object不用static 修饰时不会产生死锁，加上static就会产生死锁，为什么会这样呢？

public class TestDeadLock implements Runnable{
     static Object o1 = new Object();     //在Object前面加static与不加对synchronized有什么影响，为什么执行结果不一样
     static Object o2 = new Object();    //synchronized参数都可以是什么
     public  int flag = 0;
    public static void main(String[] args){
        TestDeadLock td1 = new TestDeadLock();
        TestDeadLock td2 = new TestDeadLock();
        td1.flag=1;
        td2.flag=0;
        Thread t1 = new Thread(td1);
        Thread t2 = new Thread(td2);
        t1.start();
        t2.start();
    }

    public void run(){
        System.out.println("flag="+flag);
        if(flag==0){
            synchronized(o1){
                try{
                    Thread.sleep(1000);
                }catch(InterruptedException e){
                    e.printStackTrace();
                    }

                synchronized(o2){
                    System.out.println("hello");
                }
            }
        }
        if(flag==1){
            synchronized(o2){
                try{
                    Thread.sleep(1000);
                }catch(InterruptedException e){
                    e.printStackTrace();
                    }

                synchronized(o1){
                    System.out.println("ok");
                }
            }
        }
    }
}