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Java Forum / General / September 2007Enumset
I was thinking of writing some JNI to access the Windows file attributes. On the Java side this would be an EnumSet. On the Windows side it would be a bitmap. Are there are any fast ways to interconvert?  SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com On Aug 31, 4:08 am, Roedy Green <see_webs...@mindprod.com.invalid> wrote: > I was thinking of writing some JNI to access the Windows file > attributes. On the Java side this would be an EnumSet. On the Windows [quoted text clipped - 3 lines] > Roedy Green Canadian Mind Products > The Java Glossaryhttp://mindprod.com Fast, as in optimal, or Fast as in, takes less than 5 minutes to create? I don't know much about JNI, but I think my approach would be have this method be private, and simply return the bitmap value (in a int value, or is possible, a BitSet). Then convert it to a BitSet. Have the enums declared in the order that the BitSet reports the bits, and use bitSet.nextSet() (I think thats the name) to determine the ordinal of the enum you want to add to the EnumSet. So, in other words, the conversion would be done on the Java side, and you don't need to worry about performance until you find it to be a bottleneck. On Fri, 31 Aug 2007 16:08:06 -0000, Daniel Pitts <googlegroupie@coloraura.com> wrote, quoted or indirectly quoted someone who said : >So, in other words, the conversion would be done on the Java side, and >you don't need to worry about performance until you find it to be a >bottleneck. When you write a library routine, you want it fast since others may use it in many contexts, including examining the attributes of every file on disk. It is frustrating knowing that EnumSat has a bitmask inside, which is just what I want to get or give. I have asked Sun for a getBitMask method. To give someone a get/put of Windows file attributes, it will have to construct the Enumset bit by bit. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com On Fri, 31 Aug 2007 21:19:02 GMT, Roedy Green <see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted someone who said : >To give someone a get/put of Windows file attributes, it will have to >construct the Enumset bit by bit. Perhaps I can cache some of the most common patterns. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Roedy Green schrieb: > On Fri, 31 Aug 2007 21:19:02 GMT, Roedy Green > <see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted [quoted text clipped - 4 lines] > > Perhaps I can cache some of the most common patterns. Why do you wan't to use EnumSet? it does not define more methods than the set interface. So you could just use a normal set. Create it by copy paste the sourcecode of RegularEnumSet and add a method to directly access the bitmap. Where is the problem? Forceing it to be of instance EnumSet seems just to make your work harder without any positive effect. Christian >So you could just use a normal set. Create it by copy paste the >sourcecode of RegularEnumSet and add a method to directly access the >bitmap. Where is the problem? Forceing it to be of instance EnumSet >seems just to make your work harder without any positive effect. four reasons: 1. your code-cloning approach would work fine for in-house, but would not be legal for free distribution. 2. I write most of my code with the intent they be teaching examples. I like to do demonstrate the use of standard classes. 3. People seem to have forgotten the art of boolean logic with bitmaps. EnumSet encapsulates it at a higher level. 4. With an EnumSet rather than named bit mask constants I have type safety. I think all I would need is an int bitmap for a roll-your-own sit of bit map constants. This is an objection to just handing over a raw int bitmap to represent the attributes. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Roedy Green schrieb: >> So you could just use a normal set. Create it by copy paste the >> sourcecode of RegularEnumSet and add a method to directly access the [quoted text clipped - 5 lines] > 1. your code-cloning approach would work fine for in-house, but would > not be legal for free distribution. I don't know the license under with java is .. I just assumed copying would be legal.. > 2. I write most of my code with the intent they be teaching examples. > I like to do demonstrate the use of standard classes. I do just think in this case you are enforceing a standard class because you want it not because it would be reasonable to use it. > 3. People seem to have forgotten the art of boolean logic with > bitmaps. EnumSet encapsulates it at a higher level. again no hindrance to roll your own enum set.. > 4. With an EnumSet rather than named bit mask constants I have type > safety. I think all I would need is an int bitmap for a roll-your-own > sit of bit map constants. This is an objection to just handing over a > raw int bitmap to represent the attributes. with your own self created kind of set you have type safety too (besides the possibility to simply add some boolean setters like setArchived(boolean archieved); I would never never advertise the use of a plain int.. Though I am also assumeing that you are overuseing enums here.. If I wanted to manipulate and read out File attributes.. I would be happy with just one class that wraps jni. with the possibility to ask for each attribute with setters and getters.. and if you want to use Enums then some method like set(FileAttributeEnum e, boolean enabled); would be most useful to me ... the retrieval of an EnumSet would be one of the last methods that would really often be in use.. and there you then have imho 2 possibilitys.. either use the Set interface and implement it like RegularEnumSet or use reflections to change the bitmap of RegularEnumSet directly. Though I would rather recommend the first one. Reuse of api classes yes but not if they don't fit or would foce me to resort to such kind of reflection work.. and as you have a very special need (high speed by directly manipulating the bitmap) well EnumSet doesn't fit.. Christian >I do just think in this case you are enforceing a standard class because >you want it not because it would be reasonable to use it. It is certainly preferable from a teaching point of view to show how to use a standard class than to do something tricky and confusing -- showing them the entire innards of Enumset. It is also preferable from a maintenance point of view. If Sun changes the innards of Enumset, the cloned code won't automatically follow suit. If I want some speed, I may have no other option, or write a Stripped down EnumSt what has just an int instead of long[] with some of the Enumset methods removed, since I am interested in only one particular EnumSet. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com On Sat, 01 Sep 2007 11:43:36 GMT, Roedy Green <see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted someone who said : >If I want some speed, I may have no other option, or write a Stripped >down EnumSt what has just an int instead of long[] with some of the >Enumset methods removed, since I am interested in only one particular >EnumSet. The other option is to provide a classic bitmap interface, rather than an EnumSet for my Windows attribute get/setter. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com > The other option is to provide a classic bitmap interface, rather than > an EnumSet for my Windows attribute get/setter. Another option is to encapsulate the data and just provide methods, e.g., boolean isArchived() boolean isReadOnly() boolean isDirectory() boolean isHidden() etc. The fact that these are in some ways stored in a number is an implementation detail that need not be exposed. If you really want an enum representing capabilities, you can make one that works on these: enum FileCapability { CAN_READ { public boolean isAllowed(RGFile file) { return file.isAllowed(); } }, // ... ; public abstract boolean isAllowed(RGFile file); } You can the build an EnumSet only when you need it for something, using EnumSet<FileCapability> getCapabilties(); You can cache it in a transient field to avoid recreating. /L SignatureLasse Reichstein Nielsen - lrn@hotpop.com DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleDOM.html> 'Faith without judgement merely degrades the spirit divine.' > On Fri, 31 Aug 2007 21:19:02 GMT, Roedy Green > <see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted [quoted text clipped - 4 lines] > > Perhaps I can cache some of the most common patterns. IIRC, any JNI library may request and use another classes private variables. So, if you are using EnumSet, it should be safe for your JNI code to assume that it is using an instance of java.util.RegularEnumSet, with a jlong named "elements", and twiddle with it all you like. This does require a few constraints: Your enums must be aligned such that 1 << enum ordinal == Windows bitmask from WinNT.h, so it means you'll probably have to stuff your Enum with some RESERVED/PLACEHOLDER Enums to fill in between undeclared gaps, like: #define FILE_ATTRIBUTE_SYSTEM 0x00000004 #define FILE_ATTRIBUTE_DIRECTORY 0x00000010 Also, assuming your code would allow setting attributes, then it would need to either enforce the use of EnumSet as a parameter, or if it allows just Set, it would have to provide an alternate mechanism for setting attributes if the user is not using an EnumSet (ala Collections.synchronizedSet, or HashSet). And, as long as you provide an alternate method, then you can fail gracefully for the oddball cases, like GNU classpath, which could set up the classes entirely differently. HTH, -Zig Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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