Re: Using "synchronized" but still getting IllegalMonitorStateException

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 6 Apr 2009 11:35:38 -0700 (PDT)

Message-ID:

<59c27e37-14fa-45b5-937c-e3d4fb47fd8d@f19g2000yqo.googlegroups.com>

laredotornado wrote:

I'm trying to execute this bit of JUnit test code (Java 1.5):

public void testEventLoggerFailure() {
try {

Try using gentler indentation on Usenet!

       synchronized(this) {
         EventLogger el = new EventLogger(null,
           null,
           null,
           null);
         el.start();
         el.wait();
       } // synchronized
    } catch (Exception e) {
      e.printStackTrace();
      fail(e.getMessage());
    } // catch
  } // testEventLoggerFailure

but yet, at the "el.wait()" line the below exceptioin is thrown ...

java.lang.IllegalMonitorStateException: current thread not owner
   at java.lang.Object.wait(Native Method)

Robert Klemme wrote:

You can only wait on the monitor that you are holding, i.e. "this" in
the case above. Frankly, I have no idea what you are trying to achieve
with the code and it seems you do not know how synchronized, wait and
notify work. I suggest you get yourself a copy of Doug Lea's book:

http://www.informit.com/store/product.aspx?isbn=0201310090&rll=1

A great book.

You can also refer to the Javadoc for 'wait()':
<http://java.sun.com/javase/6/docs/api/java/lang/Object.html#wait()>
where it makes the same point.

The Javadocs are the first line of defense against an error in an API
call.

Well, they ought to be, at least.

It's also a good idea for every Java programmer to be cognizant of the
behavior of at least java.lang.Object's methods.

--
Lew