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Interface Run Time Identification

Posted on 2009-05-19
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Last Modified: 2012-05-07
Hi Experts,

I have one interface as below:

public interface Constant {
    public enum Info {
        INFO1(4),
        INFO2(5),
        INFO3(6),
        INFO4(7),
        INFO5(8),
        INFO6(9),
        INFO7(10);
       
        private int index;

        Info(int index) {
            this.index = index;
        }
    }
}

I have a class ConstantUtil which implements the Constants interface with a method to return the Enum value of the given index.

public class ConstantUtil implements Constants
{
      public static Constants.Info getConstant (int index)
      {
            return Enum.valueOf(Constants.Info.class, "INFO" + index);
      }
}

Now, I have a requirement as below:

I have different type of Constants like ConstantA, ConstantB, etc. with the same Enum declarations but the INFO index will be different. For example INFO1(4) will be like INFO1(9) and so on.

I want to have one common util class with a method to return the corresponding Constants value.

The getConstant method must return the value from the corresponding Constants interface.

How can I do this?

Thanks,
Rameshbabu Arjuna Rajan
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Comment
Question by:arjunarajan
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14 Comments
 
LVL 92

Expert Comment

by:objects
Comment Utility
Don't think you can sorry.
0
 
LVL 86

Expert Comment

by:CEHJ
Comment Utility
You could do something like
public class ConstantUtil implements Constants

{

      public static Constants.Info getConstant (Class constantsClass, int index)

      {

            return Enum.valueOf(constantsClass, "INFO" + index);

      }

}

Open in new window

0
 

Author Comment

by:arjunarajan
Comment Utility
Hi CEHJ,

Thank you for responding quickly.

Sorry, I just forgot that you are the one who gave me the solutions for the question related to the same thing earlier.

Hope you know the history of the question and hence I am not explaining them.

If I pass Class as parameter. How can I pass it to this method from the calling method since we have the interfaces (ConstantA, ConstantB, etc)

Thanks
Rameshbabu Arjuna Rajan
0
 
LVL 92

Expert Comment

by:objects
Comment Utility
> How can I pass it to this method from the calling method since we have the interfaces (ConstantA, ConstantB, etc)

you can't

0
 
LVL 86

Expert Comment

by:CEHJ
Comment Utility
>>Hope you know the history of the question and hence I am not explaining them.

Well i can only remember vaguely now, but it looks to me like you're heading into (possibly unecessarily) complex territory and these things have a way of getting increasingly complex.

I think perhaps you could be losing sight of the functional requirement and your thinking might have got locked into the abstraction itself - always a Bad Thing. Can you explain your functional requirement, your Use Case?
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LVL 92

Expert Comment

by:objects
Comment Utility
What you are attempting will not work sorry. You need to do it differently, perhaps an index or mapping may be better suited.

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Author Comment

by:arjunarajan
Comment Utility
I have different type of records (ARecord, BRecord, etc).

All the records have this INFO values like INFO1, INFO2, etc in an array. but the thing is the array index of the INFO1, INFO2, etc will differ from each record type.

So I created an ENUM for every record type with its corresponding array index in the info index. INFO1(3), INFO2 (4), etc.

Now, when I get the type of the record during the run-time and I want to know the array index of INFO1, INFO2, etc for that particular record type, how can I write a getConstant method for that ?

0
 
LVL 92

Expert Comment

by:objects
Comment Utility
Sounds like you should just be using an index for each class with a single shared enum.
That way you could use the index to lookup the appropriate enum value for that class.

though what are the enums actually used for?

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Author Comment

by:arjunarajan
Comment Utility
Not using single shared enum for class index.

I have different interfaces for each record type with enum representing its INFO index as mentioned above.

I want to get the corresponding interface object when I use the Enum.valueOf to find the INFO index.
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Expert Comment

by:objects
Comment Utility
And as I explained above that won't work.
I'm wondering why you are using an enum at all?

0
 
LVL 86

Expert Comment

by:CEHJ
Comment Utility
>>Now, when I get the type of the record during the run-time and I want to know the array index of INFO1, INFO2, etc for that particular record type, how can I write a getConstant method for that ?

I don't see the problem there: each Record type would simply return the index of ifs own (private) enum
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LVL 92

Expert Comment

by:objects
Comment Utility
Instead of having a different enum for each class keep an index that maps the array index to the appropriate Contants.Info
0
 
LVL 92

Accepted Solution

by:
objects earned 400 total points
Comment Utility
class Constants2
{
   private int[] index = new int[] { 3, 4 };

      public Constants.Info getConstant (int index)
      {
            return Enum.valueOf(Constants.Info.class, "INFO" + index[index]);
      }


you can have a getIndex() method in a base class if you wanted which you could then use from your utils method'

      public static Constants.Info getConstant (Constant constant, int index)
      {
            return constant.getIndex(index);
      }

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