Something like contains any for Java set

Question

I have two sets  A and B  of the same type   I have to find if A contains any element from the set B   What would be the best way to do that without iterating over the sets  The Set library has contains object  and containsAll collection   but not containsAny collection

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You can use retainAll method and get the intersection of your two sets

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A good way to implement containsAny for sets is using the Guava Sets intersection     containsAny would return a boolean  so the call looks like   Sets intersection set1  set2  isEmpty     This returns true iff the sets are disjoint  otherwise false  The time complexity of this is likely slightly better than retainAll because you dont have to do any cloning to avoid modifying your original set

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Use retainAll   in the Set interface  This method provides an intersection of elements common in both sets  See the API docs for more information

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Apache Commons has a method CollectionUtils containsAny

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There s a bit rough method to do that   If and only if the A set contains some B s element than the call  A removeAll B    will modify the A set  In this situation removeAll will return true  As stated at removeAll docs   But probably you don t want to modify the A set so you may think to act on a copy  like this way   new HashSet A  removeAll B    and the returning value will be true if the sets are not distinct  that is they have non-empty intersection     Also see Apache Commons Collections

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I would recommend creating a HashMap from set A  and then iterating through set B and checking if any element of B is in A  This would run in O  A   B   time  as there would be no collisions   whereas retainAll Collection lt   gt  c  must run in O  A   B   time

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I use  org apache commons collections CollectionUtils  CollectionUtils containsAny someCollection1  someCollection2    That is All  Returns true if at least one element is in both collections   Simple to use  and the name of the function is more suggestive

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Wouldn t Collections disjoint A  B  work  From the documentation      Returns true if the two specified collections have no elements in common    Thus  the method returns false if the collections contains any common elements

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Stream  anyMatch  Since Java 8 you could use Stream  anyMatch    setA stream   anyMatch setB  contains

[java] Something like 'contains any' for Java set?

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