Re: enums, using methods as initializers

Daniel Pitts <>
Thu, 15 Nov 2007 13:17:27 -0800
mekane wrote:

Mikhail Teterin wrote:


I would like to be able to initialize fields of an enum with /methods/
another Class).

Here is the (non-working) example:

 import java.util.*;
 import java.sql.*;

 public enum Field {
  FIELD1 (ResultSet.getString),
  FIELD2 (ResultSet.getDouble),
  FIELDN (ResultSet.getTimestamp);

  private java.lang.reflect.Method extract;

the idea is to be able to get all fields from a given ResultSet by going
through the list of Fields and extracting the column from the ResultSet.

Something like:

 public void print(ResultSet rs)
  for (Field f : Field.values())
   System.out.println(f + ":\t" + rs.f.extract(f));

Does the above stand a chance of being turned into a real Java code?

Thanks for ideas!


I assume you've looked at:

I had a case where I needed to do something similar to this, and I tried
overriding a method on each element of the enum. I didn't like defining
big methods inside the constructor, so I actually went with the method
described in the article that uses a switch.

So you would have one method defined in the enum like:

  public String extract( Resultset arg ){
    switch ( this )
      case FIELD1:
        return arg.getString();
      case FIELD2:
        return arg.getDouble();
      case FIELDN:
        return resultSet.getTimestamp();

then you could iterate over the values of the enum and do f.extract(rs)


That is very specifically a Bad Idea!
f.extract should NOT have a switch statement, but instead should be

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