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thanks, very helpful your explanation
cz
"dar7yl" <no@reply.org> escribi� en el mensaje 
news:41b0cd56@newsgroups.borland.com...
> "Carlos Zin" <nomailplease@hotmail.com> wrote in message 
> news:41afa7d8$1@newsgroups.borland.com...
>> Please suppose I have the following case where Tool is a class defined 
>> somewhere else:
>>
>> public class ToolFactory {
>>    private class A extends Tool {}
>>    private class B extends Tool {}
>>    public static Tool makeTool(String toolName) {
>>        if (toolName == "A")
>>            return new A();
>>        else if (toolName == "B")
>>            return new B();
>>        else
>>            return null;
>>    }
>> }
>>
>> I am trying to build a static factory method named "makeTool()" which 
>> produces instances of classes A and B but the compiler complain telling 
>> that non-static variable this cannot be referenced from a static context.
>>
>> Making the method non-static eliminate the error but then I need to make 
>> an instance of Toolfactory in order to access method makeTool(s) which is 
>> not what I want. I need to call "ToolFactory.makeTool(s)", i.e. a static 
>> method with no object instance.
>> How can I solve this problem?
>
> You can make A and B static classes:
>
> <code>
>  private static class A extends Tool {}
>  private static class B extends Tool {}
> </code>
>
> Otherwise, you must have a singleton instance of your ToolFactory class 
> which provides the environment (ie class variables) which can be accessed 
> by your subclasses, if desired.
> viz:
> <code>
> public class ToolFactory
> {
>    private class A extends Tool {}
>    private class B extends Tool {}
>
>    // place class variables here, if desired,
>    // and objects of A and B can access them.
>
>    // static singleton instance
>    private static ToolFactory factoryInstance = null;
>
>    // private constructor enforces Singleton pattern
>    private ToolFactory ()
>    {
>        // Initialize class variables here
>    }
>
>    public static Tool makeTool(String toolName)
>   {
>        // singleton auto-constructor
>        if (factoryInstance ==  null)
>            factoryInstance = new ToolFactory ();
>
>        if (toolName == "A")
>            return new factoryInstance.A();
>        else if (toolName == "B")
>            return new factoryInstance.B();
>        else
>            return null;
>    }  // makeTool
> } // ToolFactory
> </code>
>
>
> regards,
>    Dar7yl
>
>
>
>
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