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 is null ? e is null : 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
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 is null ? e is null : 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