public static <E> SetView<E> difference(final Set<E> set1, final Set<?> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    return new SetView<E>() {
      @Override
      public UnmodifiableIterator<E> iterator() {
        return new AbstractIterator<E>() {
          final Iterator<E> itr = set1.iterator();

          @Override
          protected E computeNext() {
            while (itr.hasNext()) {
              E e = itr.next();
              if (!set2.contains(e)) {
                return e;
              }
            }
            return endOfData();
          }
        };
      }

      @Override
      public int size() {
        int size = 0;
        for (E e : set1) {
          if (!set2.contains(e)) {
            size++;
          }
        }
        return size;
      }

      @Override
      public boolean isEmpty() {
        return set2.containsAll(set1);
      }

      @Override
      public boolean contains(Object element) {
        return set1.contains(element) && !set2.contains(element);
      }
    };
  }
public static <E> SetView<E> difference(final Set<E> set1, final Set<?> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    return new SetView<E>() {
      @Override
      public UnmodifiableIterator<E> iterator() {
        return new AbstractIterator<E>() {
          final Iterator<E> itr = set1.iterator();

          @Override
          protected E computeNext() {
            while (itr.hasNext()) {
              E e = itr.next();
              if (!set2.contains(e)) {
                return e;
              }
            }
            return endOfData();
          }
        };
      }

      @Override
      public int size() {
        int size = 0;
        for (E e : set1) {
          if (!set2.contains(e)) {
            size++;
          }
        }
        return size;
      }

      @Override
      public boolean isEmpty() {
        return set2.containsAll(set1);
      }

      @Override
      public boolean contains(Object element) {
        return set1.contains(element) && !set2.contains(element);
      }
    };
  }
public static < E > SetView < E > difference ( final Set < E > set1 , final Set < ? > set2 ) { checkNotNull ( set1 , "set1" ) ; checkNotNull ( set2 , "set2" ) ; return new SetView < E > ( ) { @ Override public UnmodifiableIterator < E > iterator ( ) { return new AbstractIterator < E > ( ) { final Iterator < E > itr = set1 . iterator ( ) ; @ Override protected E computeNext ( ) { while ( itr . hasNext ( ) ) { E e = itr . next ( ) ; if ( ! set2 . contains ( e ) ) { return e ; } } return endOfData ( ) ; } } ; } @ Override public int size ( ) { int size = 0 ; for ( E e : set1 ) { if ( ! set2 . contains ( e ) ) { size ++ ; } } return size ; } @ Override public boolean isEmpty ( ) { return set2 . containsAll ( set1 ) ; } @ Override public boolean contains ( Object element ) { return set1 . contains ( element ) && ! set2 . contains ( element ) ; } } ; }
Returns an unmodifiable <b>view</b> of the difference of two sets. The returned set contains
all elements that are contained by {@code set1} and not contained by {@code set2}. {@code set2}
may also contain elements not present in {@code set1}; these are simply ignored. The iteration
order of the returned set matches that of {@code set1}.

<p>Results are undefined if {@code set1} and {@code set2} are sets based on different
equivalence relations (as {@code HashSet}, {@code TreeSet}, and the keySet of an {@code
IdentityHashMap} all are).
Returns an unmodifiable <b > view< / b > of the difference of two sets . The returned set contains all elements that are contained by { @code set1 } and not contained by { @code set2 } . { @code set2 } may also contain elements not present in { @code set1 } ; these are simply ignored . The iteration order of the returned set matches that of { @code set1 } .