New Client Reply: Generics in ucar.ma2 Dear John, I read your e-mail and thought about it. So to start with, the idea of Generics is to avoid 'runtime-typing' like casts and reflections (getclass()) and let the compiler check as much types as possible. 100% type safety is guaranteed then. The tutorial http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf is good and explaining how to integrate generics into old code/APIs, too. I think you better read it twice. It is a disadvantage that arrays in Java are 'covariant', i.e. Object  is a real superclass of String . That is from a generic point of view not correct since e.g.: Object[ ] objArr; String[ ] strArr = new String; objArr = strArr; // objArr = new Integer(5); //loss in information by this assignment but more important: apparently sufficient information (int > obj) for this assignment String string = strArr; //runtime exception! strArr returns a Integer To understand this one has to think in terms of "write-access" and "read-access" on objects. If you have an Object objArr its ok to write some subtype into it: objArr = new Integer(5). But it is NOT ok to read a subtype from it: int test = objArr. This idea is not only true for a single assignments but for complete methods. Imagine a generic method (a method with generic object as argument): - which only reads from the generic type, e.g. from 'number', then calling this method with a Float as argument instead of a Number is ok, too. You should declare it with <? extends Number>. - On the other side, if a method is write Numbers (e.g. adds into an array of Numbers) this will not work for Floats but maybe for Objects, so you can write <? super Number>. This is called bounded wildcards (compare 4.1). Because arrays are covariant and a contradiction to invariant generic objects it is unfortunately not allowed to make a generic array (of doubles, ints, floats whatever): T genericArray = new T; I think the thousand lines of ucar.ma would reduce to rather one then Yet, I think there are a lot of possibilities in ucar.ma where it is possible to use generics. Make a new generic Class <T> Array Hold in this class empty arrays float , short , long  etc. In constructor reflect type T.getclass() and initialize corresponding array . Another point is the dimensionality of the matrices. First of all, I wonder that you are not making use of any 'final' statements. I think you should use them whenever possible to improve performance. And then I wonder why you have implementation D0..D7 and not just use an access-method with loops over their dimensions. A constructor Array(<T>, int d) would initialize the final dimension. And then the most delicate part has to be implemented, think about all the methods, which parts of them are necessary (for example, I would prefer omitting the getDouble(), getFloat() methods etc) and replace it by getValue(), according to the initialized Array<T>), whenever there is something type-specific in the code it probably can be replaced by T or ?. After all I would implement a new version with probably different API and deprecate the old one. I hope that you are not frightened and think about it. Letting the compiler do as much type-checking as possible is not a bad idea. Maybe the code can be also reduced a lot. If you thought about it a while , please let me know! Best regards, Georg -----UrsprÃngliche Nachricht----- Von: Unidata netCDF Java Support [mailto:address@hidden Gesendet: Freitag, 19. August 2011 18:12 An: Steidl, Georg Betreff: [netCDFJava #KSI-560385]: Generics in ucar.ma2 Hi Georg: As you can tell, the Array classes preceded java generics. I use them wherever I can, but I dont understand them deep enough to actually write classes that implement them. So the short answer is i'd love to have you contribute to that. However, I would guess that it would be hard to make this backwards compatible (?) If so, I would have to think carefully about how/if we could do this, or if we would need to make a new version with a different API. What do you think? John > Hello NetCDF-Developers! > > I am really glad that there are projects like NetCDF-Java that you have > created. Since I got more familiar with Java Generics now I thought > whether you think about implementing ucar.ma2 and all the Array Stuff > with templates. > > Is there something planned? If yes, I would like to contribute to that. > > Regards, > Georg Steidl > > -- > M.Sc. Comp. Engineering > > Deutsches Zentrum fÃr Luft- und Raumfahrt e. V. | German Aerospace Center > Institut fÃr Aerodynamik und StrÃmungstechnik | Institute of > Aerodynamics and Flow Technology > Abteilung Hubschrauber | Department Helicopters > > Lilienthalplatz 7, 38108 Braunschweig, Germany > Tel : +49 (0)531 295 3306 > > > Ticket Details =================== Ticket ID: KSI-560385 Department: Support netCDF Java Priority: High Status: Open Ticket Details =================== Ticket ID: KSI-560385 Department: Support netCDF Java Priority: High Status: Open Link: https://www.unidata.ucar.edu/esupport/staff/index.php?_m=tickets&_a=viewticket&ticketid=18590 Ticket Details =================== Ticket ID: KSI-560385 Department: Support netCDF Java Priority: High Status: Open
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