🚀 go-pugleaf

On 12/2/2004 at 6:41:23 PM, Carlos Zin wrote:

> 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.

Classes A and B are non-static.  That means that require an enclosing
instance of class ToolFactory, and that is passed to their constructors as
a hidden argument.  From a non-static context of ToolFactory, the compiler
will automatically pass the current instance (this) to the constructor.
From a static context or from outside of class ToolFactory, you must
specify the ToolFactory instance to provide to the constructor.  That is
done using the syntax:

    toolFactoryInstance.new A();
    toolFactoryInstance.new B();

If these classes need to reference non-static members of ToolFactory, you
will need to provide the enclosing instance to the constructor as shown
above.  If not, just declare classes A and B as static.

One more note:

>         if (toolName == "A")

>         else if (toolName == "B")

I think you want to use:

          if (toolName.equals("A"))

          else if (toolName.equals("B"))

-- 
Regards,

John McGrath [TeamB]

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