<window title="test of long operation" border="normal">
<zscript> <![CDATA[
import org.zkoss.zk.ui.event.*;

EventQueue eq = EventQueues.lookup("longop");

String result = "";

eq.subscribe(new EventListener() {
public void onEvent(Event evt)

{ //asynchronous org.zkoss.lang.Threads.sleep(3000); //simulate a long operation result = "success"; //store the result }

}, new EventListener() { //callback
public void onEvent(Event evt)

{ alert("evt shall not be null: "+evt); lb.value = result; }

});
]]> </zscript>
<button label="async long op" onClick='eq.publish(new Event("whatever"));'/>
<label id="lb"/>
</window>