How to calculate the intersection of two sets

Question

Possible Duplicate    Efficiently finding the intersection of a variable number of sets of strings       Say  have two Hashset  how to calculate the intersection of them   Set lt String gt  s1   new HashSet lt String gt      Set lt String gt  s2   new HashSet lt String gt      S1 INT S2

User · Answer

Yes there is retainAll check out this  Set lt Type gt  intersection   new HashSet lt Type gt  s1   intersection retainAll s2

User · Answer

Use the retainAll   method of Set   Set lt String gt  s1  Set lt String gt  s2  s1 retainAll s2      s1 now contains only elements in both sets   If you want to preserve the sets  create a new set to hold the intersection   Set lt String gt  intersection   new HashSet lt String gt  s1      use the copy constructor intersection retainAll s2     The javadoc of retainAll   says it s exactly what you want      Retains only the elements in this set that are contained in the specified collection  optional operation   In other words  removes from this set all of its elements that are not contained in the specified collection  If the specified collection is also a set  this operation effectively modifies this set so that its value is the intersection of the two sets

[java] How to calculate the intersection of two sets?

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