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Java Forum / General / December 2007How to create a class with given fields?
Hi, It's hard to explain why I need this, but I need to programmatically create a class that has certain fields in it. For examle, is it possible to write a function class MyClass { public static Class createClass(String field1, String field2) { } } that creates a class with two int fields whose names are contained in variables field1 and field2. Many thanks in advance!!! Aaron >I need to programmatically create a class You can use the compiler API to programmatically create a class, if you are using Sun's Java implementation and the JDK is available. For an example that creates the class »ExpressionWrapper«, see http://www.purl.org/stefan_ram/pub/evaluating-expressions-with-java >>I need to programmatically create a class >You can use the compiler API Without it, you can still write a class file, even with only the JRE. To do this, you need to learn the class file format. Then you can write them using java.io and load them with a class loader. If all classes only need to consist of some String fields, you can also create some such class files with the compiler and then inspect their format to learn the format for this special simple case. >Hi, > >It's hard to explain why I need this, .. I don't care why *you* need this. Try explaining it to me as if I were an end user. In terms of.. "This software offers YYY' where YYY is something that I, as an end user might, GAF* about. * 'Give A ..Flying care'  SignatureAndrew Thompson http://www.physci.org/ >Hi, > [quoted text clipped - 16 lines] > >Aaron If all your fields are to be Integers than you could build the class as a wrapper round a HashMap<String, Integer>. The constructor could take an array (or List) of Strings as a parameter so you could put as many entries in the HashMap as you needed. The getter and setter would each take a String parameter to indicate which entry in the HashMap (i.e. which field) to get or set. rossum >> It's hard to explain why I need this, but I need to programmatically >> create a class that has certain fields in it. > If all your fields are to be Integers than you could build the class > as a wrapper round a HashMap<String, Integer>. The constructor could > take an array (or List) of Strings as a parameter so you could put as > many entries in the HashMap as you needed. The getter and setter > would each take a String parameter to indicate which entry in the > HashMap (i.e. which field) to get or set. Right. And you could put anything in there, not just Integers, if you use Objects instead of Integers. This I think is similar to what the ResultSet object does when it returns rows from a database. Largely, you are responsible for sorting out the type of the objects. If you really need to build a class like the compiler does, you are in for a lot of work, and the result could be hard to maintain and modify. If you can get by with a list of Objects in an array or a Collection, you'll be much happier. And it'll be much easier to fob the result off on some new guy. (Software engineering hint: always think exit strategy.) > (Software engineering hint: always think exit strategy.) Business hint: same. Conflict hint: same. Relationship hint: same. Life hint: same. SignatureLew > It's hard to explain why I need this, but I need to programmatically > create a class that has certain fields in it. [quoted text clipped - 10 lines] > that creates a class with two int fields whose names are contained in > variables field1 and field2. Several tools to do so exist: BCEL javassist ASM Try and see which one suits you. Arne 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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