Jakarta Commons Cookbook

5.16. Transforming Collections

Problem

You need to perform a transformation using each element in a Collection.

Solution

Use CollectionUtils.transform() . Supply a Collection and a Transformer to this method, and this utility will pass each element in the Collection to that Transformer, returning a new Collection containing the results of each transformation. The following example demonstrates the use of transform( ) with a custom Transformer object:

import java.util.*;
import org.apache.commons.collections.Transformer;
import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.lang.ArrayUtils;
import org.apache.commons.lang.StringUtils;

// Create a transformer that reverses strings.
               Transformer reversingTransformer = new Transformer( ) {
                   public Object transform(Object object) {
                       String string = (String) object;
                       return StringUtils.reverse( string );
                   }
               }

String[] array = new String[] { "Aznar", "Blair", "Chirac", "Putin", "Bush" };
List stringList = Arrays.asList( ArrayUtils.clone( array ) );

// Transform each element with a Transformer
               CollectionUtils.transform( stringList, reversingTransformer );

System.out.println( "Original: " + ArrayUtils.toString( array ) );
System.out.println( "Transformed: " + 
                    ArrayUtils.toString( stringList.toArray( ) ) );

This example creates a List of strings, transforming each element with a Transformer that produces reversed strings. The List is transformed in-place, which means that the contents of the List are replaced with the ...