关于object的wait和notity

起初想测试下，object的notifyAll和notify方法，关于notifyAll和notify，jdk的说明文档已经讲的很清楚了，这里再说明下

notifyAll是唤醒在该对象上所有等待该对象monitor的线程。关于monitor，其实还是有些说法的，Java对象是天生的Monitor，这句话大家应该好好理解下，可以参考http://www.cnblogs.com/tomsheep/archive/2010/06/09/1754419.html。

* Wakes up all threads that are waiting on this object's monitor. A
* thread waits on an object's monitor by calling one of the
* {@code wait} methods.

notify是随机唤醒某个在该对象上等待monitor的线程。

* Wakes up a single thread that is waiting on this object's
* monitor. If any threads are waiting on this object, one of them
* is chosen to be awakened. The choice is arbitrary and occurs at
* the discretion of the implementation. A thread waits on an object's
* monitor by calling one of the {@code wait} methods.

起初，代码上这样写的：public class TestObjectNotify {

   private static Object object = new Object();
   public static void main(String[] args) {
         final int i = 0;
         Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
               beginWait(i);
            }
         }) ;
         thread.start();
         
         final int j = 1;
         Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
               beginWait(j);
            }
         }) ;
         thread2.start();
         
         final int k = 8;
         Thread thread3 = new Thread(new Runnable() {
            @Override
            public void run() {
               beginWait(k);
            }
         }) ;
         thread3.start();
         
         try {
            Thread.sleep(3000);
         } catch (InterruptedException e) {
            e.printStackTrace();
         }
         
         try {
            Thread.sleep(3000);
         } catch (InterruptedException e) {
            e.printStackTrace();
         }
         System.out.println("-----------notifyAll-------------");
         
         object.notifyAll();
   }
   
   public static void beginWait(int i) {
      try {
         object.wait();
      } catch (InterruptedException e) {
         e.printStackTrace();
      }
   
   }
   
   public static void beginNotify() {
      System.out.println("-----------notify-------------");
      object.notify();
   }
}

当运行的时候，熟悉object的notify和notifyAll的同学可能已经看到问题了，会报一个异常
java.lang.IllegalMonitorStateException

其实在调用这三个方法的时候，一定要获取到该对象的锁，才能正确调用该方法，
后来改为如下的方式，就没问题了。关于具体原因，可以参考 http://www.cnblogs.com/techyc/p/3272321.html

synchronized (object) {
   object.notifyAll();
}

synchronized (object) {
   object.wait();

}