@Override
    public boolean isDone() {
        stateLock.lock();
        try {
            return finished || cancelled || (exception != null);
        } finally {
            stateLock.unlock();
        }
    }
Create an <code>AppTask</code> that will execute the given 
{@link Callable}.

@param callable The callable to be executed
jme3-core/src/main/java/com/jme3/app/AppTask.java