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Java Forum / General / November 2007Extending Inner Classes
Hello, I have checked my Java In a nutshell, and Sun's documentation, and either there is no answer, or more likely I am asking it wrong when. I have a package Some Data. A Class DataGroup1 A Method public ParseData getParseData ParseData retValue = new ParseData(args,args....); return retValue; A Public Static InnerClass ParseData A Method Public getParsedData A Class DataGroup2 extends DataGroup1 A Method public ParseData getParseData ParseData retValue = new ParseData(args,args....); return retValue; A Public Static InnerClass ParseData A Method Public getParsedData The problem I am getting is I cannot seem to overide the superclasses method as DataGroup1.ParseData is a different return type than DataGroup2.ParseData. Am I doint something impossible as it is layed out above? I thought about making the inner class it's own separate class in the package, but if I do I would prefer it was 'protected' to be only viewable to classes in that package and do not know how to accomplish that. I could also just make the inner class part of the DataGroup Classes, but that would require some serious re-coding. Any suggestions, or hints would be greatly appreciated! Thanks Ryan > Hello, > [quoted text clipped - 26 lines] > accomplish that. I could also just make the inner class part of the > DataGroup Classes, but that would require some serious re-coding. You have declared two unrelated classes DataGroup1.ParseData and DataGroup2.ParseData. In DataGroup2 you want a static inner class ParseData2 that extends ParseData. Alternately, getParseData() could return an interface type and DataGroup and DataGroup2 could both implement that interface. Even though DataGroup2 would not extend DataGroup in that case, you should still name it DataGroup2 or something else other than DataGroup to avoid confusion. > you want a static inner class ... Then you should prepare for disappointment: <http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.1.3> > An inner class is a nested class that is not explicitly or implicitly declared static.  SignatureLew Thanks to all for your help. > There is no such thing as a "static inner class". An inner class is not static, > by definition. You mean a static nested class. My apologies, I am still somewhat of a new programmer to Java, I did not realize a static nested class existed. I usually do not use classes inside classes as I do not fully see a use for them, the program I inherited, already had this static nested class. > You can make it a top-level class and declare it as package-private (no access > modifier whatsoever). Thanks to Lew and lyallex (for your example), I have decided it's best for me to create a top level class and have my two classes DataGroup1 and DataGroup2 access code from the ParseData class that way instead of using an inner static class. Again thanks for your help! Lew wrote: >> There is no such thing as a "static inner class". > My apologies, To whom are you apologizing? I don't think the JLS has feelings. The purpose of this newsgroup is to disseminate and discuss knowledge of Java programming. None of us knew any of this until we learned it. All of us have much to learn still. SignatureLew > I have a package Some Data. > A Class DataGroup1 [quoted text clipped - 12 lines] > A Public Static InnerClass ParseData > A Method Public getParsedData I am not able to compile your example. <http://www.physci.org/codes/sscce.html> There is no such thing as a "static inner class". An inner class is not static, by definition. You mean a static nested class. > The problem I am getting is I cannot seem to overide the superclasses > method as DataGroup1.ParseData is a different return type than > DataGroup2.ParseData. Am I doint something impossible as it is layed > out above? I cannot say because you have not provided any code, but it looks wrong on the face of it. You say "ParseData()" is a method, but you spell it with an initial upper-case letter and indicate constructor syntax for it, which means it's a class and not a method. You have "ParseData" in every outer and nested class. You don't show the subclass is supposed to use ParseData, nor which one it's supposed to use. Your example is a mess. Review <http://www.physci.org/codes/sscce.html> and try again. > I thought about making the inner class it's own separate class in the package, but if I do I would prefer it was 'protected' to > be only viewable to classes in that package and do not know how to > accomplish that. You can make it a top-level class and declare it as package-private (no access modifier whatsoever). It can even be in the same source file as a public class, although that's probably not wise. > I could also just make the inner class part of the DataGroup Classes, but that would require some serious re-coding. Your outline suggest that you've already made the (not inner) nested class part of the DataGroup class(es?). > Any suggestions, or hints would be greatly appreciated! Provide an example we can actually run through our compilers. <http://www.physci.org/codes/sscce.html> More importantly, tell us what you're trying to accomplish. Not the specific strategy of overriding ParseData, whatever you think that might mean, but the goal of what such an ovverride is supposed to accomplish. If we don't know what you're trying to accomplish it's hard to help. <http://www.physci.org/codes/sscce.html> SignatureLew > I thought about making the inner class it's own separate > class in the package, but if I do I would prefer it was 'protected' to > be only viewable to classes in that package and do not know how to > accomplish that. //Bar.java a public class in package com.foo package com.foo; public class Bar { } //Foo.java a class with 'default' visibility in package com.foo package com.foo; class Foo { } //Baz.java a client in package com.foo.baz package com.foo.baz; import com.foo.*; public class Baz { //OK, Bar is public Bar b = new Bar(); //Won't compile, Foo only visible //to classes in package com.foo Foo f = new Foo(); } Give the class default or package private visibility. You do this by omitting any visibility modifier (public, abstract, final). Of course I'm sure someone will come up with an answer to the rest of your quetion 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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