求集合的交集

 import java.util.*;

 public class Test{

 public static void main(String[] args) {
  Set<Integer> a = new HashSet<Integer>(Arrays.asList(1, 2, 3, 4, 5));
      Set<Integer> b = new HashSet<Integer>(Arrays.asList(3, 4, 6, 7, 8));
      Set<Integer> c = new HashSet<Integer>(Arrays.asList(4, 5, 8, 9, 0));
      Set<Integer> aIntersectsB = setIntersect(a, b);
      Set<Integer> aIntersectsC = setIntersect(a, c);
      Set<Integer> bIntersectsC = setIntersect(b, c);
      Set<Integer> abc = setIntersect(a, bIntersectsC);
     
      System.out.println("a ∩ b: " + aIntersectsB);
      System.out.println("a ∩ c: " + aIntersectsC);
      System.out.println("b ∩ c: " + bIntersectsC);
      System.out.println("a ∩ b ∩ c: " + abc);

        }
       /**
  * 求两个Set集合的交集，移除 set1 中所有未包含在指定 set2 中的元素
  * @param <E>
  * @param set1
  * Set集合对象
  * @param set2
  * Set集合对象
  * @return
  * Set集合的一个实例，该实例是两个Set的交集
  */
 private static <E> Set<E> setIntersect(Set<E> set1, Set<E> set2) {
  
  if(set1==null||set2==null){
   return new HashSet<E>();
  }
  Set<E> intersectSet = new HashSet<E>(set1);
     intersectSet.retainAll(set2);
   return intersectSet;
 }
}