关于!$assertionsDisabled

源码：

assert ((WeakReference)oIterActive).get() == iter;//注意条件相反

反编译后：

static final boolean $assertionsDisabled; /* synthetic field */
 
            if(!$assertionsDisabled && ((WeakReference)oIterActive).get() != iter)
                throw new AssertionError();
 
    static 
    {
        $assertionsDisabled = !(SafeHashMap.class).desiredAssertionStatus();
    }