contains
Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that Objects.equals(o, e).
Return
true if this set contains the specified element
Parameters
o
object to be checked for containment in this set
Throws
if the specified object cannot be compared with the elements currently in the set
if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements