public boolean containsKey(Object key) {
        int hash = hash(key.hashCode());
        return segmentFor(hash).containsKey(key, hash);
    }
Tests if the specified object is a key in this table.

@param  key   possible key
@return <tt>true</tt> if and only if the specified object
        is a key in this table, as determined by the
        <tt>equals</tt> method; <tt>false</tt> otherwise.
@throws NullPointerException if the specified key is null
commons-profiler/src/main/java/com/navercorp/pinpoint/common/profiler/concurrent/jsr166/ConcurrentWeakHashMap.java