.IllegalMonitorStateException报错

我有一段这样的代码
Dotry try1=new Dotry("线程1");
Dotry try2=new Dotry("线程2");
try1.start();
try1.join();
Thread.sleep(2000);
try1.wait();
try2.start();
调试后报错我想问一下时怎么回事啊？
class Dotry extends Thread{
String name;
public Dotry(String name){
this.name=name;
}
public void run(){
for(int i=15;i>0;i--){
System.out.println(name+"在运行");
}
}

}

http://macleo.iteye.com/blog/625873

如果当前线程不是此对象监视器的所有者，就会抛出该异常，也就是说调用wait方法之前，必须先获取该对象的同步监视器。正确的使用语法必须是：

 synchronized(try1){
                try1.wait();
            }

其实你可以F3看下这个wait方法的源码，API文档的注释是这样的：

      * <pre>
     *     synchronized (obj) {
     *         while (&lt;condition does not hold&gt;)
     *             obj.wait();
     *         ... // Perform action appropriate to condition
     *     }
     * </pre>
     * This method should only be called by a thread that is the owner
     * of this object's monitor. See the {@code notify} method for a
     * description of the ways in which a thread can become the owner of
     * a monitor.