Knowing subclasses of a class


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Thread: Knowing subclasses of a class

  1. #1
    mehul joshi Guest

    Knowing subclasses of a class


    Hi,

    Is there any way in java by which i can know all the sub-classes of a given
    class ( Here class can be a userdefined class or a system class). Similarly
    can i know all the classes of a particular package in Java.

    Regards

  2. #2
    Kevin Casault Guest

    Re: Knowing subclasses of a class


    "mehul joshi" <mjoshi@onebox.com> wrote:
    >
    >Hi,
    >
    >Is there any way in java by which i can know all the sub-classes of a given
    >class ( Here class can be a userdefined class or a system class). Similarly
    >can i know all the classes of a particular package in Java.
    >
    >Regards


    The Java API and for user defined class documentation is the key. There
    is no easy way that I know of find the information you want.

  3. #3
    Paul Clapham Guest

    Re: Knowing subclasses of a class


    mehul joshi <mjoshi@onebox.com> wrote in message
    news:39474c17$1@news.devx.com...
    >
    > Hi,
    >
    > Is there any way in java by which i can know all the sub-classes of a

    given
    > class ( Here class can be a userdefined class or a system class).

    Similarly
    > can i know all the classes of a particular package in Java.
    >
    > Regards


    That depends on what you mean by "i". If you want to know this, then you
    should look in the documentation. But if you want a Java program to be able
    to find this out, I'd suggest looking through the file system for files with
    a ".class" extension. A couple of problems I foresee you having with this:
    (1) you need to be able to find out what the classpath is -- is there a
    system property for this? -- and watch out for the Java2 extension
    mechanism, where the lib directory in the JRE is implicitly part of the
    classpath (2) you need to be able to look inside .jar files in the
    classpath -- they're formatted just like zip files, so you can do that.
    Likewise if you want your program to know all the classes in a package, just
    do the same thing for its directory path.





  4. #4
    mehul joshi Guest

    Re: Knowing subclasses of a class


    "Paul Clapham" <pclapham@core-mark.com> wrote:
    >
    >mehul joshi <mjoshi@onebox.com> wrote in message
    >news:39474c17$1@news.devx.com...
    >>
    >> Hi,
    >>
    >> Is there any way in java by which i can know all the sub-classes of a

    >given
    >> class ( Here class can be a userdefined class or a system class).

    >Similarly
    >> can i know all the classes of a particular package in Java.
    >>
    >> Regards

    >
    >That depends on what you mean by "i". If you want to know this, then you
    >should look in the documentation. But if you want a Java program to be

    able
    >to find this out, I'd suggest looking through the file system for files

    with
    >a ".class" extension. A couple of problems I foresee you having with this:
    >(1) you need to be able to find out what the classpath is -- is there a
    >system property for this? -- and watch out for the Java2 extension
    >mechanism, where the lib directory in the JRE is implicitly part of the
    >classpath (2) you need to be able to look inside .jar files in the
    >classpath -- they're formatted just like zip files, so you can do that.
    >Likewise if you want your program to know all the classes in a package,

    just
    >do the same thing for its directory path.
    >
    >
    >
    >

    Hi Paul,

    Actually i wanted to know it programmatically (just like finding methods
    of a class in Reflection).

    Regards


  5. #5
    Paul Clapham Guest

    Re: Knowing subclasses of a class


    mehul joshi <mjoshi@onebox.com> wrote in message
    news:39530e09$1@news.devx.com...
    >
    > "Paul Clapham" <pclapham@core-mark.com> wrote:
    > >
    > >mehul joshi <mjoshi@onebox.com> wrote in message
    > >news:39474c17$1@news.devx.com...
    > >>
    > >> Hi,
    > >>
    > >> Is there any way in java by which i can know all the sub-classes of a

    > >given
    > >> class ( Here class can be a userdefined class or a system class).

    > >Similarly
    > >> can i know all the classes of a particular package in Java.
    > >>
    > >> Regards

    > >
    > >That depends on what you mean by "i". If you want to know this, then you
    > >should look in the documentation. But if you want a Java program to be

    > able
    > >to find this out, I'd suggest looking through the file system for files

    > with
    > >a ".class" extension. A couple of problems I foresee you having with

    this:
    > >(1) you need to be able to find out what the classpath is -- is there a
    > >system property for this? -- and watch out for the Java2 extension
    > >mechanism, where the lib directory in the JRE is implicitly part of the
    > >classpath (2) you need to be able to look inside .jar files in the
    > >classpath -- they're formatted just like zip files, so you can do that.
    > >Likewise if you want your program to know all the classes in a package,

    > just
    > >do the same thing for its directory path.
    > >
    > >
    > >
    > >

    > Hi Paul,
    >
    > Actually i wanted to know it programmatically (just like finding methods
    > of a class in Reflection).
    >
    > Regards
    >

    Yes, I know that's what you wanted. But the Reflection API can only reflect
    on objects that have been instantiated in a program. And if you create 7
    subclasses of a class, the only way for Reflection to know that would be for
    you to instantiate an object of each of those 7 subclasses... which means
    you already know the answer.




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