Re: Java type-casting -- Q3

grz01 wrote:


Type-safe heterogeneous containers: Effective Java, Joshua Bloch. I
just whipped this up, it's untested ('cept for the short static method
at the end).

Note: I've never needed to use one of these either.

import java.util.HashMap;
import java.util.Map;

/** A type safe heterogeneous container.
  *
  * @author Brenden
  */
public class HeterogeneousContainer {

     Map<String,Class<?>> namesAndTypes;
     Map<String,Object> values;

     public HeterogeneousContainer( Map<String, Class<?>> namesAndTypes )
     {
         this.namesAndTypes = new HashMap<String,Class<?>>( namesAndTypes );
         values = new HashMap<String,Object>( namesAndTypes.size() );
     }

     public <T> T get( String name, Class<T> type ) {
         if( type == namesAndTypes.get( name ) ) {
             return (T) values.get( name );
         }
         else {
             throw new IllegalArgumentException( "Pair (" + name + ", "+
                     type+") do not exist." );
         }
     }

     public <T> T put( String name, Class<T> type, T value ) {
         if( type == namesAndTypes.get( name ) ) {
             return (T) values.put( name, value );
         }
         else {
             throw new IllegalArgumentException( "Pair (" + name + ", "+
                     type+") do not exist." );
         }
     }

     public static void main( String[] args )
     {
         HashMap<String,Class<?>> namesAndTypes = new
HashMap<String,Class<?>>();
         namesAndTypes.put( "first", String.class );
         namesAndTypes.put( "second", Integer.class );
         HeterogeneousContainer test = new HeterogeneousContainer(
namesAndTypes );
         test.put( "first", String.class, "A String");
         test.put( "second", Integer.class, 4 );
         String s = test.get( "first", String.class );
         Integer i = test.get( "second", Integer.class );
         System.out.println( "Values: " + s + i );
     }
}