通过使用泛型方法和Set来表达数学中的表达式：集合的交并补，在以下3个方法中都将第1个参数Set复制了1份，并未直接修改参数中Set。
package Set;
import java.util.HashSet;
import java.util.Set;
public class Sets {
public static <T> Set<T> intersection(Set<T> s1, Set<T> s2) {
Set<T> result = new HashSet<T>(s1);
result.retainAll(s2);
return result;
}
public static <T> Set<T> union(Set<T> s1, Set<T> s2) {
Set<T> result = new HashSet<T>(s1);
result.addAll(s2);
return result;
}
//Subtract subset from superset
public static <T> Set<T> difference (Set<T> superset, Set<T> subset) {
Set<T> result = new HashSet<T>(superset);
result.addAll(subset);
return result;
}
//Reflexive --everything not in their intersection
public static <T> Set<T> complement(Set<T>s1,Set<T> s2){
return difference(union(s1,s2),intersection(s1,s2));
}
}