@Override
    public boolean contains(Object o) {
        return map.containsKey(o);
    }
Returns <tt>true</tt> if this set contains the specified element. More
formally, returns <tt>true</tt> if and only if this set contains an
element <tt>e</tt> such that
<tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.

@param o element whose presence in this set is to be tested
@return <tt>true</tt> if this set contains the specified element
core/common/src/main/java/com/alipay/sofa/rpc/common/struct/ConcurrentHashSet.java