EnumSet--what the...?

Discussion in 'Java' started by George Cherry, Jul 9, 2005.

  1. "Roedy Green" <> wrote in message
    > On Fri, 8 Jul 2005 14:16:46 -0400, "George Cherry"
    > <> wrote or quoted :
    >>Yes, I said something similar (but not so well)
    >>in an earlier post to Roedy. Hey Roedy, Java's
    >>a high-level language; get your mind out of the
    >>bit gutter. : o )

    > my background is math. I expect operations like union, intersection,
    > on something that calls itself a set, which map very nicely to what an
    > assembler programmer like me does with bitmaps. It turns out the
    > interesting methods of an EnumSet are way down in the AbstractSet
    > class.

    Okay, but Joshua Bloch's elegant Collections Framework
    gives you all the set operations--and they work between different
    Set implementations (including EnumSet) very conveniently.
    EnumSet implements the Collections Framework's root
    interface, Collection, and, of course, its subinterface, Set.
    It turns out that EnumSet's relevant bulk operations are
    way up in the Collection interface, and they are defined
    explicitly as set operations in the API for the Set interface.
    (Are interfaces neat or what?)

    Bloch's excellent tutorial on the Java Collections Framework
    is at


    The following is from the tutorial

    The bulk operations are particularly well suited to Sets; when applied to
    sets, they perform standard set-algebraic operations. Suppose s1 and s2 are
    Sets. Here's what the bulk operations do:
    a.. s1.containsAll(s2): Returns true if s2 is a subset of s1. (s2 is a
    subset of s1 if set s1 contains all the elements in s2.)
    b.. s1.addAll(s2): Transforms s1 into the union of s1 and s2. (The union
    of two sets is the set containing all the elements contained in either set.)
    c.. s1.retainAll(s2): Transforms s1 into the intersection of s1 and s2.
    (The intersection of two sets is the set containing only the elements that
    are common to both sets.)
    d.. s1.removeAll(s2): Transforms s1 into the (asymmetric) set difference
    of s1 and s2. (For example, the set difference of s1 - s2 is the set
    containing all the elements found in s1 but not in s2.)
    > There seems to be a heck of a lot of dithering compared with the way I
    > implemented such a feature in Abundance.

    Fooling around directly with bits is a heck of a lot of dithering compared
    with the way Bloch specified and implemented set operations in the
    Java Collections Framework--and you still get the efficiency of bit
    vector dithering, because the implementation of EnumSet uses bit
    vectors behind the high level scene.

    George W. Cherry
    George Cherry, Jul 9, 2005
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