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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-24) make Configuration an interface
Date Thu, 18 May 2006 03:12:07 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-24?page=comments#action_12412285 ] 

Konstantin Shvachko commented on HADOOP-24:
-------------------------------------------

I think that all declarations and parameters should say Configuration that is the interface.
And the constructors should be the only places where ConfigurationImpl
appears explicitly. E.g. all occurrences
      private static ConfigurationImpl conf = new ConfigurationImpl();
should be replaced by
      private static Configuration conf = new ConfigurationImpl();
I haven't seen a lot of nutch code, but if it uses only the API, then
that should work. If it does construct config instances then there should be
a static newInstance() somewhere I guess.


> make Configuration an interface
> -------------------------------
>
>          Key: HADOOP-24
>          URL: http://issues.apache.org/jira/browse/HADOOP-24
>      Project: Hadoop
>         Type: Improvement

>   Components: conf
>     Reporter: Doug Cutting
>  Attachments: HADOOP-24-2.patch, HADOOP-24-3.patch, HADOOP-24.patch, HADOOP-24.patch
>
> The Configuration class should become an interface, e.g.:
> public interface Configuration {
>   String get(String nam);
>   String set(String name, String value);
>   int getInt(String name);
>   void setInt(String name, int value);
>   float getFloat(String name);
>   void setFloat(String name, float value);
>   //... other utility methods based on get(String) and set(String,String) ...
> }
> An abstract class named ConfigurationBase should be implemented as follows:
> public abstract class ConfigurationBase implements Configuration {
>   abstract public String get(String nam);
>   abstract public String set(String name, String value);
>   public  int getInt(String name) { ... implementation in terms of get(String) ... }
>   public void setInt(String name, int value) {... implementation in terms of set(String,
String) ...}
>   public float getFloat(String name)  { ... implementation in terms of get(String) ...
}
>   public void setFloat(String name, float value)  {... implementation in terms of set(String,
String) ...}
>   //... other utility methods based on get(String) and set(String,String) ...
> }
> A concrete, default implementation will be provided as follows:
> public class ConfigurationImpl implements Writable extends ConfigurationBase {
>   private Properties properties;
>   // implement abstract methods from ConfigurationBase
>   public String get(String name) { ... implemented in terms of props ...}
>   public String set(String name, String value) { .. implemented in terms of props ...
}
>   // Writable methods
>   public write(DataOutputStream out);
>   public readFields(DataInputStream in);
>   // permit chaining of configurations
>   public Configuration getDefaults();
>   public void setDefaults(Configuration defaults);
> }
> Only code which creates configurations should need to be updated, so this shouldn't be
a huge change.

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